< draft-ietf-mpls-rfc3036bis   rfc5036.txt 
Network Working Group Loa Andersson Network Working Group L. Andersson, Ed.
Internet Draft Ina Minei Request for Comments: 5036 Acreo AB
Expiration Date: March 2007 Bob Thomas Obsoletes: 3036 I. Minei, Ed.
Editors Category: Standards Track Juniper Networks
B. Thomas, Ed.
September 2006 Cisco Systems, Inc.
October 2007
LDP Specification LDP Specification
draft-ietf-mpls-rfc3036bis-04.txt Status of This Memo
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Source of this document
This document is produced as part of advancing the LDP specification This document specifies an Internet standards track protocol for the
to draft standard status. The LDP specification was originally Internet community, and requests discussion and suggestions for
published as RFC 3036 in January 2001. It was produced by the MPLS improvements. Please refer to the current edition of the "Internet
working of the IETF and was jointly authored by Loa Andersson, Paul Official Protocol Standards" (STD 1) for the standardization state
Doolan, Nancy Feldman, Andre Fredette and Bob Thomas. and status of this protocol. Distribution of this memo is unlimited.
Abstract Abstract
The architecture for Multi Protocol Label Switching (MPLS) is The architecture for Multiprotocol Label Switching (MPLS) is
described in RFC 3031 [RFC3031]. A fundamental concept in MPLS is described in RFC 3031. A fundamental concept in MPLS is that two
that two Label Switching Routers (LSRs) must agree on the meaning of Label Switching Routers (LSRs) must agree on the meaning of the
the labels used to forward traffic between and through them. This labels used to forward traffic between and through them. This common
common understanding is achieved by using a set of procedures, called understanding is achieved by using a set of procedures, called a
a label distribution protocol, by which one LSR informs another of label distribution protocol, by which one LSR informs another of
label bindings it has made. This document defines a set of such label bindings it has made. This document defines a set of such
procedures called LDP (for Label Distribution Protocol) by which LSRs procedures called LDP (for Label Distribution Protocol) by which LSRs
distribute labels to support MPLS forwarding along normally routed distribute labels to support MPLS forwarding along normally routed
paths. paths.
Table of Contents Table of Contents
Source of this document ............................... 1 1. LDP Overview ....................................................5
1 LDP Overview .......................................... 7 1.1. LDP Peers ..................................................6
1.1 LDP Peers ............................................. 8 1.2. LDP Message Exchange .......................................6
1.2 LDP Message Exchange .................................. 8 1.3. LDP Message Structure ......................................7
1.3 LDP Message Structure ................................. 9 1.4. LDP Error Handling .........................................7
1.4 LDP Error Handling .................................... 9 1.5. LDP Extensibility and Future Compatibility .................7
1.5 LDP Extensibility and Future Compatibility ............ 9 1.6. Specification Language .....................................7
1.6 Specification Language ................................ 9 2. LDP Operation ...................................................8
2 LDP Operation ......................................... 10 2.1. FECs .......................................................8
2.1 FECs .................................................. 10 2.2. Label Spaces, Identifiers, Sessions, and Transport .........9
2.2 Label Spaces, Identifiers, Sessions and Transport ..... 11 2.2.1. Label Spaces ........................................9
2.2.1 Label Spaces .......................................... 11 2.2.2. LDP Identifiers .....................................9
2.2.2 LDP Identifiers ....................................... 11 2.2.3. LDP Sessions .......................................10
2.2.3 LDP Sessions .......................................... 12 2.2.4. LDP Transport ......................................10
2.2.4 LDP Transport ......................................... 12
2.3 LDP Sessions between non-Directly Connected LSRs ...... 12 2.3. LDP Sessions between Non-Directly Connected LSRs ..........10
2.4 LDP Discovery ......................................... 13 2.4. LDP Discovery .............................................11
2.4.1 Basic Discovery Mechanism ............................. 13 2.4.1. Basic Discovery Mechanism ..........................11
2.4.2 Extended Discovery Mechanism .......................... 13 2.4.2. Extended Discovery Mechanism .......................11
2.5 Establishing and Maintaining LDP Sessions ............ 14 2.5. Establishing and Maintaining LDP Sessions .................12
2.5.1 LDP Session Establishment ............................. 14 2.5.1. LDP Session Establishment ..........................12
2.5.2 Transport Connection Establishment .................... 15 2.5.2. Transport Connection Establishment .................12
2.5.3 Session Initialization ................................ 16 2.5.3. Session Initialization .............................14
2.5.4 Initialization State Machine .......................... 19 2.5.4. Initialization State Machine .......................16
2.5.5 Maintaining Hello Adjacencies ......................... 21 2.5.5. Maintaining Hello Adjacencies ......................19
2.5.6 Maintaining LDP Sessions .............................. 21 2.5.6. Maintaining LDP Sessions ...........................19
2.6 Label Distribution and Management ..................... 22 2.6. Label Distribution and Management .........................20
2.6.1 Label Distribution Control Mode ....................... 22 2.6.1. Label Distribution Control Mode ....................20
2.6.1.1 Independent Label Distribution Control ................ 22 2.6.1.1. Independent Label Distribution Control ....20
2.6.1.2 Ordered Label Distribution Control .................... 22 2.6.1.2. Ordered Label Distribution Control ........20
2.6.2 Label Retention Mode .................................. 23 2.6.2. Label Retention Mode ...............................21
2.6.2.1 Conservative Label Retention Mode ..................... 23 2.6.2.1. Conservative Label Retention Mode .........21
2.6.2.2 Liberal Label Retention Mode .......................... 24 2.6.2.2. Liberal Label Retention Mode ..............21
2.6.3 Label Advertisement Mode .............................. 24 2.6.3. Label Advertisement Mode ...........................22
2.7 LDP Identifiers and Next Hop Addresses ................ 24 2.7. LDP Identifiers and Next Hop Addresses ....................22
2.8 Loop Detection ........................................ 25 2.8. Loop Detection ............................................23
2.8.1 Label Request Message ................................. 26 2.8.1. Label Request Message ..............................23
2.8.2 Label Mapping Message ................................. 27 2.8.2. Label Mapping Message ..............................25
2.8.3 Discussion ............................................ 29 2.8.3. Discussion .........................................26
2.9 Authenticity and Integrity of LDP Messages ............ 29 2.9. Authenticity and Integrity of LDP Messages ................27
2.9.1 TCP MD5 Signature Option .............................. 30 2.9.1. TCP MD5 Signature Option ...........................27
2.9.2 LDP Use of TCP MD5 Signature Option ................... 31 2.9.2. LDP Use of TCP MD5 Signature Option ................29
2.10 Label Distribution for Explicitly Routed LSPs ......... 32 2.10. Label Distribution for Explicitly Routed LSPs ............29
3 Protocol Specification ................................ 32 3. Protocol Specification .........................................30
3.1 LDP PDUs .............................................. 32 3.1. LDP PDUs ..................................................30
3.2 LDP Procedures ........................................ 33 3.2. LDP Procedures ............................................31
3.3 Type-Length-Value Encoding ............................ 34 3.3. Type-Length-Value Encoding ................................31
3.4 TLV Encodings for Commonly Used Parameters ............ 35 3.4. TLV Encodings for Commonly Used Parameters ................33
3.4.1 FEC TLV ............................................... 36 3.4.1. FEC TLV ............................................33
3.4.1.1 FEC Procedures ........................................ 37 3.4.1.1. FEC Procedures ............................35
3.4.2 Label TLVs ............................................ 38 3.4.2. Label TLVs .........................................35
3.4.2.1 Generic Label TLV ..................................... 38 3.4.2.1. Generic Label TLV .........................36
3.4.2.2 ATM Label TLV ......................................... 38 3.4.2.2. ATM Label TLV .............................36
3.4.2.3 Frame Relay Label TLV ................................. 39 3.4.2.3. Frame Relay Label TLV .....................37
3.4.3 Address List TLV ...................................... 40 3.4.3. Address List TLV ...................................38
3.4.4 Hop Count TLV ......................................... 41 3.4.4. Hop Count TLV ......................................39
3.4.4.1 Hop Count Procedures .................................. 41 3.4.4.1. Hop Count Procedures ......................39
3.4.5 Path Vector TLV ....................................... 43 3.4.5. Path Vector TLV ....................................41
3.4.5.1 Path Vector Procedures ................................ 43 3.4.5.1. Path Vector Procedures ....................41
3.4.5.1.1 Label Request Path Vector ............................. 43 3.4.5.1.1. Label Request Path Vector ......41
3.4.5.1.2 Label Mapping Path Vector ............................. 44 3.4.5.1.2. Label Mapping Path Vector ......42
3.4.6 Status TLV ............................................ 45 3.4.6. Status TLV .........................................43
3.5 LDP Messages .......................................... 46
3.5.1 Notification Message .................................. 49 3.5. LDP Messages ..............................................44
3.5.1.1 Notification Message Procedures ....................... 50 3.5.1. Notification Message ...............................46
3.5.1.2 Events Signaled by Notification Messages .............. 50 3.5.1.1. Notification Message Procedures ...........48
3.5.1.2.1 Malformed PDU or Message .............................. 51 3.5.1.2. Events Signaled by Notification Messages ..48
3.5.1.2.2 Unknown or Malformed TLV .............................. 52 3.5.1.2.1. Malformed PDU or Message .......48
3.5.1.2.3 Session KeepAlive Timer Expiration .................... 52 3.5.1.2.2. Unknown or Malformed TLV .......49
3.5.1.2.4 Unilateral Session Shutdown ........................... 52 3.5.1.2.3. Session KeepAlive Timer
3.5.1.2.5 Initialization Message Events ......................... 52 Expiration .....................50
3.5.1.2.6 Events Resulting From Other Messages .................. 53 3.5.1.2.4. Unilateral Session Shutdown ....50
3.5.1.2.7 Internal Errors ....................................... 53 3.5.1.2.5. Initialization Message Events ..50
3.5.1.2.8 Miscellaneous Events .................................. 53 3.5.1.2.6. Events Resulting from
3.5.2 Hello Message ......................................... 53 Other Messages .................50
3.5.2.1 Hello Message Procedures .............................. 55 3.5.1.2.7. Internal Errors ................51
3.5.3 Initialization Message ................................ 57 3.5.1.2.8. Miscellaneous Events ...........51
3.5.3.1 Initialization Message Procedures ..................... 65 3.5.2. Hello Message ......................................51
3.5.4 KeepAlive Message ..................................... 65 3.5.2.1. Hello Message Procedures ..................53
3.5.4.1 KeepAlive Message Procedures .......................... 65 3.5.3. Initialization Message .............................54
3.5.5 Address Message ....................................... 66 3.5.3.1. Initialization Message Procedures .........63
3.5.5.1 Address Message Procedures ............................ 66 3.5.4. KeepAlive Message ..................................63
3.5.6 Address Withdraw Message .............................. 67 3.5.4.1. KeepAlive Message Procedures ..............63
3.5.6.1 Address Withdraw Message Procedures ................... 68 3.5.5. Address Message ....................................64
3.5.7 Label Mapping Message ................................. 68 3.5.5.1. Address Message Procedures ................64
3.5.7.1 Label Mapping Message Procedures ...................... 69 3.5.6. Address Withdraw Message ...........................65
3.5.7.1.1 Independent Control Mapping ........................... 70 3.5.6.1. Address Withdraw Message Procedures .......66
3.5.7.1.2 Ordered Control Mapping ............................... 70 3.5.7. Label Mapping Message ..............................66
3.5.7.1.3 Downstream on Demand Label Advertisement .............. 71 3.5.7.1. Label Mapping Message Procedures ..........67
3.5.7.1.4 Downstream Unsolicited Label Advertisement ............ 71 3.5.7.1.1. Independent Control Mapping ....67
3.5.8 Label Request Message ................................. 72 3.5.7.1.2. Ordered Control Mapping ........68
3.5.8.1 Label Request Message Procedures ...................... 73 3.5.7.1.3. Downstream on Demand
3.5.9 Label Abort Request Message ........................... 74 Label Advertisement ............68
3.5.9.1 Label Abort Request Message Procedures ................ 75 3.5.7.1.4. Downstream Unsolicited
3.5.10 Label Withdraw Message ................................ 77 Label Advertisement ............69
3.5.10.1 Label Withdraw Message Procedures ..................... 78 3.5.8. Label Request Message ..............................70
3.5.11 Label Release Message ................................. 78 3.5.8.1. Label Request Message Procedures ..........71
3.5.11.1 Label Release Message Procedures ...................... 79 3.5.9. Label Abort Request Message ........................72
3.6 Messages and TLVs for Extensibility ................... 80 3.5.9.1. Label Abort Request Message Procedures ....73
3.6.1 LDP Vendor-private Extensions ......................... 80 3.5.10. Label Withdraw Message ............................74
3.6.1.1 LDP Vendor-private TLVs ............................... 80 3.5.10.1. Label Withdraw Message Procedures ........75
3.6.1.2 LDP Vendor-private Messages ........................... 82 3.5.11. Label Release Message .............................76
3.6.2 LDP Experimental Extensions ........................... 83 3.5.11.1. Label Release Message Procedures .........77
3.7 Message Summary ....................................... 84 3.6. Messages and TLVs for Extensibility .......................78
3.8 TLV Summary ........................................... 84 3.6.1. LDP Vendor-Private Extensions ......................78
3.9 Status Code Summary ................................... 85 3.6.1.1. LDP Vendor-Private TLVs ...................78
3.10 Well-known Numbers .................................... 86 3.6.1.2. LDP Vendor-Private Messages ...............80
3.10.1 UDP and TCP Ports ..................................... 86 3.6.2. LDP Experimental Extensions ........................81
3.10.2 Implicit NULL Label ................................... 86 3.7. Message Summary ...........................................81
4 IANA Considerations ................................... 87 3.8. TLV Summary ...............................................82
4.1 Message Type Name Space ............................... 87 3.9. Status Code Summary .......................................83
4.2 TLV Type Name Space ................................... 87 3.10. Well-Known Numbers .......................................84
4.3 FEC Type Name Space ................................... 88 3.10.1. UDP and TCP Ports .................................84
4.4 Status Code Name Space ................................ 88 3.10.2. Implicit NULL Label ...............................84
4.5 Experiment ID Name Space .............................. 88 4. IANA Considerations ............................................84
5 Security Considerations ............................... 89 4.1. Message Type Name Space ...................................84
5.1 Spoofing .............................................. 89 4.2. TLV Type Name Space .......................................85
5.2 Privacy ............................................... 90 4.3. FEC Type Name Space .......................................85
5.3 Denial of Service ..................................... 90 4.4. Status Code Name Space ....................................86
6 Areas for Future Study ................................ 92 4.5. Experiment ID Name Space ..................................86
7 Changes from RFC3036 .................................. 93 5. Security Considerations ........................................86
8 Acknowledgments ....................................... 95 5.1. Spoofing ..................................................86
9 References ............................................ 96 5.2. Privacy ...................................................87
9.1 Normative references .................................. 96 5.3. Denial of Service .........................................88
9.2 Non-normative references .............................. 96 6. Areas for Future Study .........................................89
10 Intellectual Property Statement ....................... 97 7. Changes from RFC 3036 ..........................................90
11 Editors' Addresses .................................... 98 8. Acknowledgments ................................................93
Appendix A LDP Label Distribution Procedures ..................... 99 9. References .....................................................93
A.1 Handling Label Distribution Events .................... 101 9.1. Normative References ......................................93
A.1.1 Receive Label Request ................................. 102 9.2. Informative References ....................................94
A.1.2 Receive Label Mapping ................................. 105 Appendix A. LDP Label Distribution Procedures ....................95
A.1.3 Receive Label Abort Request ........................... 111 A.1. Handling Label Distribution Events .......................97
A.1.4 Receive Label Release ................................. 113 A.1.1. Receive Label Request .............................98
A.1.5 Receive Label Withdraw ................................ 115 A.1.2. Receive Label Mapping ...........................101
A.1.6 Recognize New FEC ..................................... 117 A.1.3. Receive Label Abort Request .....................107
A.1.7 Detect Change in FEC Next Hop ......................... 119 A.1.4. Receive Label Release ...........................109
A.1.8 Receive Notification / Label Request Aborted .......... 122 A.1.5. Receive Label Withdraw ..........................111
A.1.9 Receive Notification / No Label Resources ............. 123 A.1.6. Recognize New FEC ...............................113
A.1.10 Receive Notification / No Route ....................... 123 A.1.7. Detect Change in FEC Next Hop ...................115
A.1.11 Receive Notification / Loop Detected .................. 124 A.1.8. Receive Notification / Label Request Aborted ....118
A.1.12 Receive Notification / Label Resources Available ...... 125 A.1.9. Receive Notification / No Label Resources .......119
A.1.13 Detect local label resources have become available .... 126 A.1.10. Receive Notification / No Route ................119
A.1.14 LSR decides to no longer label switch a FEC ........... 127 A.1.11. Receive Notification / Loop Detected ...........120
A.1.15 Timeout of deferred label request ..................... 127 A.1.12. Receive Notification / Label Resources Available 121
A.2 Common Label Distribution Procedures .................. 128 A.1.13. Detect Local Label Resources Have Become
A.2.1 Send_Label ............................................ 128 Available ......................................122
A.2.2 Send_Label_Request .................................... 130 A.1.14. LSR Decides to No Longer Label Switch a FEC ....123
A.2.3 Send_Label_Withdraw ................................... 131 A.1.15. Timeout of Deferred Label Request ..............123
A.2.4 Send_Notification ..................................... 131 A.2. Common Label Distribution Procedures ....................124
A.2.5 Send_Message .......................................... 132 A.2.1. Send_Label ......................................124
A.2.6 Check_Received_Attributes ............................. 132 A.2.2. Send_Label_Request ..............................125
A.2.7 Prepare_Label_Request_Attributes ...................... 133 A.2.3. Send_Label_Withdraw .............................127
A.2.8 Prepare_Label_Mapping_Attributes ...................... 135 A.2.4. Send_Notification ...............................127
Full Copyright Statement .............................. 138 A.2.5. Send_Message ....................................128
A.2.6. Check_Received_Attributes .......................128
A.2.7. Prepare_Label_Request_Attributes ................129
A.2.8. Prepare_Label_Mapping_Attributes ................131
1. LDP Overview 1. LDP Overview
The MPLS architecture [RFC3031] defines a label distribution protocol The MPLS architecture [RFC3031] defines a label distribution protocol
as a set of procedures by which one Label Switched Router (LSR) as a set of procedures by which one Label Switched Router (LSR)
informs another of the meaning of labels used to forward traffic informs another of the meaning of labels used to forward traffic
between and through them. between and through them.
The MPLS architecture does not assume a single label distribution The MPLS architecture does not assume a single label distribution
protocol. In fact, a number of different label distribution proto- protocol. In fact, a number of different label distribution
cols are being standardized. Existing protocols have been extended protocols are being standardized. Existing protocols have been
so that label distribution can be piggybacked on them. New protocols extended so that label distribution can be piggybacked on them. New
have also been defined for the explicit purpose of distributing protocols have also been defined for the explicit purpose of
labels. The MPLS architecture discusses some of the considerations distributing labels. The MPLS architecture discusses some of the
when choosing a label distribution protocol for use in particular considerations when choosing a label distribution protocol for use in
MPLS applications such as Traffic Engineering [RFC2702]. particular MPLS applications such as Traffic Engineering [RFC2702].
The Label Distribution Protocol (LDP) is a protocol defined for dis- The Label Distribution Protocol (LDP) is a protocol defined for
tributing labels. It was originally published as RFC3036 in January distributing labels. It was originally published as RFC 3036 in
2001. It was produced by the MPLS working of the IETF and was jointly January 2001. It was produced by the MPLS Working Group of the IETF
authored by Loa Andersson, Paul Doolan, Nancy Feldman, Andre Fredette and was jointly authored by Loa Andersson, Paul Doolan, Nancy
and Bob Thomas. Feldman, Andre Fredette, and Bob Thomas.
LDP is a protocol defined for distributing labels. It is the set of LDP is a protocol defined for distributing labels. It is the set of
procedures and messages by which Label Switched Routers (LSRs) estab- procedures and messages by which Label Switched Routers (LSRs)
lish Label Switched Paths (LSPs) through a network by mapping net- establish Label Switched Paths (LSPs) through a network by mapping
work-layer routing information directly to data-link layer switched network-layer routing information directly to data-link layer
paths. These LSPs may have an endpoint at a directly attached neigh- switched paths. These LSPs may have an endpoint at a directly
bor (comparable to IP hop-by-hop forwarding), or may have an endpoint attached neighbor (comparable to IP hop-by-hop forwarding), or may
at a network egress node, enabling switching via all intermediary have an endpoint at a network egress node, enabling switching via all
nodes. intermediary nodes.
LDP associates a Forwarding Equivalence Class (FEC) [RFC3031] with LDP associates a Forwarding Equivalence Class (FEC) [RFC3031] with
each LSP it creates. The FEC associated with an LSP specifies which each LSP it creates. The FEC associated with an LSP specifies which
packets are "mapped" to that LSP. LSPs are extended through a net- packets are "mapped" to that LSP. LSPs are extended through a
work as each LSR "splices" incoming labels for a FEC to the outgoing network as each LSR "splices" incoming labels for a FEC to the
label assigned to the next hop for the given FEC. outgoing label assigned to the next hop for the given FEC.
More information about the applicability of LDP can be found in More information about the applicability of LDP can be found in
[RFC3037]. [RFC3037].
This document assumes (but does not require) familiarity with the This document assumes (but does not require) familiarity with the
MPLS architecture [RFC3031]. Note that [RFC3031] includes a glossary MPLS architecture [RFC3031]. Note that [RFC3031] includes a glossary
of MPLS terminology, such as ingress, label switched path, etc. of MPLS terminology, such as ingress, label switched path, etc.
1.1. LDP Peers 1.1. LDP Peers
Two LSRs which use LDP to exchange label/FEC mapping information are Two LSRs that use LDP to exchange label/FEC mapping information are
known as "LDP Peers" with respect to that information and we speak of known as "LDP Peers" with respect to that information, and we speak
there being an "LDP Session" between them. A single LDP session of there being an "LDP Session" between them. A single LDP session
allows each peer to learn the other's label mappings; i.e., the pro- allows each peer to learn the other's label mappings; i.e., the
tocol is bi-directional. protocol is bidirectional.
1.2. LDP Message Exchange 1.2. LDP Message Exchange
There are four categories of LDP messages: There are four categories of LDP messages:
1. Discovery messages, used to announce and maintain the presence 1. Discovery messages, used to announce and maintain the presence
of an LSR in a network. of an LSR in a network.
2. Session messages, used to establish, maintain, and terminate 2. Session messages, used to establish, maintain, and terminate
sessions between LDP peers. sessions between LDP peers.
3. Advertisement messages, used to create, change, and delete 3. Advertisement messages, used to create, change, and delete
label mappings for FECs. label mappings for FECs.
4. to signal error information. 4. Notification messages, used to provide advisory information and
to signal error information.
Discovery messages provide a mechanism whereby LSRs indicate their Discovery messages provide a mechanism whereby LSRs indicate their
presence in a network by sending a Hello message periodically. This presence in a network by sending a Hello message periodically. This
is transmitted as a UDP packet to the LDP port at the `all routers on is transmitted as a UDP packet to the LDP port at the 'all routers on
this subnet' group multicast address. When an LSR chooses to estab- this subnet' group multicast address. When an LSR chooses to
lish a session with another LSR learned via the Hello message, it establish a session with another LSR learned via the Hello message,
uses the LDP initialization procedure over TCP transport. Upon suc- it uses the LDP initialization procedure over TCP transport. Upon
cessful completion of the initialization procedure, the two LSRs are successful completion of the initialization procedure, the two LSRs
LDP peers, and may exchange advertisement messages. are LDP peers, and may exchange advertisement messages.
When to request a label or advertise a label mapping to a peer is When to request a label or advertise a label mapping to a peer is
largely a local decision made by an LSR. In general, the LSR largely a local decision made by an LSR. In general, the LSR
requests a label mapping from a neighboring LSR when it needs one, requests a label mapping from a neighboring LSR when it needs one,
and advertises a label mapping to a neighboring LSR when it wishes and advertises a label mapping to a neighboring LSR when it wishes
the neighbor to use a label. the neighbor to use a label.
Correct operation of LDP requires reliable and in order delivery of Correct operation of LDP requires reliable and in-order delivery of
messages. To satisfy these requirements LDP uses the TCP transport messages. To satisfy these requirements, LDP uses the TCP transport
for session, advertisement and notification messages; i.e., for for Session, Advertisement, and Notification messages, i.e., for
everything but the UDP-based discovery mechanism. everything but the UDP-based discovery mechanism.
1.3. LDP Message Structure 1.3. LDP Message Structure
All LDP messages have a common structure that uses a Type-Length- All LDP messages have a common structure that uses a Type-Length-
Value (TLV) encoding scheme; see Section "Type-Length-Value" encod- Value (TLV) encoding scheme; see Section "Type-Length-Value
ing. The Value part of a TLV-encoded object, or TLV for short, may Encoding". The Value part of a TLV-encoded object, or TLV for short,
itself contain one or more TLVs. may itself contain one or more TLVs.
1.4. LDP Error Handling 1.4. LDP Error Handling
LDP errors and other events of interest are signaled to an LDP peer LDP errors and other events of interest are signaled to an LDP peer
by notification messages. by Notification messages.
There are two kinds of LDP notification messages: There are two kinds of LDP Notification messages:
1. Error notifications, used to signal fatal errors. If an LSR 1. Error Notifications, used to signal fatal errors. If an LSR
receives an error notification from a peer for an LDP session, receives an Error Notification from a peer for an LDP session,
it terminates the LDP session by closing the TCP transport con- it terminates the LDP session by closing the TCP transport
nection for the session and discarding all label mappings connection for the session and discarding all label mappings
learned via the session. learned via the session.
2. Advisory notifications, used to pass an LSR information about 2. Advisory Notifications, used to pass on LSR information about
the LDP session or the status of some previous message received the LDP session or the status of some previous message received
from the peer. from the peer.
1.5. LDP Extensibility and Future Compatibility 1.5. LDP Extensibility and Future Compatibility
Functionality may be added to LDP in the future. It is likely that Functionality may be added to LDP in the future. It is likely that
future functionality will utilize new messages and object types future functionality will utilize new messages and object types
(TLVs). It may be desirable to employ such new messages and TLVs (TLVs). It may be desirable to employ such new messages and TLVs
within a network using older implementations that do not recognize within a network using older implementations that do not recognize
them. While it is not possible to make every future enhancement them. While it is not possible to make every future enhancement
skipping to change at page 10, line 11 skipping to change at page 8, line 11
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. LDP Operation 2. LDP Operation
2.1. FECs 2.1. FECs
It is necessary to precisely specify which packets may be mapped to It is necessary to precisely specify which packets may be mapped to
each LSP. This is done by providing a FEC specification for each each LSP. This is done by providing a FEC specification for each
LSP. The FEC identifies the set of IP packets which may be mapped to LSP. The FEC identifies the set of IP packets that may be mapped to
that LSP. that LSP.
Each FEC is specified as a set of one or more FEC elements. Each FEC Each FEC is specified as a set of one or more FEC elements. Each FEC
element identifies a set of packets which may be mapped to the corre- element identifies a set of packets that may be mapped to the
sponding LSP. When an LSP is shared by multiple FEC elements, that corresponding LSP. When an LSP is shared by multiple FEC elements,
LSP is terminated at (or before) the node where the FEC elements can that LSP is terminated at (or before) the node where the FEC elements
no longer share the same path. can no longer share the same path.
This specification defines a single type of FEC element, the "Address This specification defines a single type of FEC element, the "Address
Prefix FEC element". This element is an address prefix of any length Prefix FEC element". This element is an address prefix of any length
from 0 to a full address, inclusive. from 0 to a full address, inclusive.
Additional FEC elements may be defined, as needed, by other specifi- Additional FEC elements may be defined, as needed, by other
cations. specifications.
In the remainder of this section we give the rules to be used for In the remainder of this section, we give the rules to be used for
mapping packets to LSPs that have been set up using an Address Prefix mapping packets to LSPs that have been set up using an Address Prefix
FEC element. FEC element.
We say that a particular address "matches" a particular address pre- We say that a particular address "matches" a particular address
fix if and only if that address begins with that prefix. We also say prefix if and only if that address begins with that prefix. We also
that a particular packet matches a particular LSP if and only if that say that a particular packet matches a particular LSP if and only if
LSP has an Address Prefix FEC element which matches the packet's des- that LSP has an Address Prefix FEC element that matches the packet's
tination address. With respect to a particular packet and a particu- destination address. With respect to a particular packet and a
lar LSP, we refer to any Address Prefix FEC element which matches the particular LSP, we refer to any Address Prefix FEC element that
packet as the "matching prefix". matches the packet as the "matching prefix".
The procedure for mapping a particular packet to a particular LSP The procedure for mapping a particular packet to a particular LSP
uses the following rules. Each rule is applied in turn until the uses the following rules. Each rule is applied in turn until the
packet can be mapped to an LSP. packet can be mapped to an LSP.
- If a packet matches exactly one LSP, the packet is mapped to that - If a packet matches exactly one LSP, the packet is mapped to
LSP. that LSP.
- If a packet matches multiple LSPs, it is mapped to the LSP whose - If a packet matches multiple LSPs, it is mapped to the LSP
matching prefix is the longest. If there is no one LSP whose whose matching prefix is the longest. If there is no one LSP
matching prefix is longest, the packet is mapped to one from the whose matching prefix is longest, the packet is mapped to one
set of LSPs whose matching prefix is longer than the others. The from the set of LSPs whose matching prefix is longer than the
procedure for selecting one of those LSPs is beyond the scope of others. The procedure for selecting one of those LSPs is
this document. beyond the scope of this document.
- If it is known that a packet must traverse a particular egress - If it is known that a packet must traverse a particular egress
router, and there is an LSP which has an Address Prefix FEC ele- router, and there is an LSP that has an Address Prefix FEC
ment which is a /32 address of that router, then the packet is element that is a /32 address of that router, then the packet
mapped to that LSP. The procedure for obtaining this knowledge is mapped to that LSP. The procedure for obtaining this
is beyond the scope of this document. knowledge is beyond the scope of this document.
The procedure for determining that a packet must traverse a particu- The procedure for determining that a packet must traverse a
lar egress router is beyond the scope of this document. (As an exam- particular egress router is beyond the scope of this document. (As
ple, if one is running a link state routing algorithm, it may be pos- an example, if one is running a link state routing algorithm, it may
sible to obtain this information from the link state data base. As be possible to obtain this information from the link state data base.
another example, if one is running BGP, it may be possible to obtain As another example, if one is running BGP, it may be possible to
this information from the BGP next hop attribute of the packet's obtain this information from the BGP next hop attribute of the
route.) packet's route.)
2.2. Label Spaces, Identifiers, Sessions and Transport 2.2. Label Spaces, Identifiers, Sessions, and Transport
2.2.1. Label Spaces 2.2.1. Label Spaces
The notion of "label space" is useful for discussing the assignment The notion of "label space" is useful for discussing the assignment
and distribution of labels. There are two types of label spaces: and distribution of labels. There are two types of label spaces:
- Per interface label space. Interface-specific incoming labels - Per interface label space. Interface-specific incoming labels
are used for interfaces that use interface resources for labels. are used for interfaces that use interface resources for
An example of such an interface is a label-controlled ATM inter- labels. An example of such an interface is a label-controlled
face that uses VCIs as labels, or a Frame Relay interface that ATM interface that uses VCIs (Virtual Channel Identifiers) as
uses DLCIs (Data Link Connection Identifiers) as labels. labels, or a Frame Relay interface that uses DLCIs (Data Link
Connection Identifiers) as labels.
Note that the use of a per interface label space only makes sense Note that the use of a per interface label space only makes
when the LDP peers are "directly connected" over an interface, sense when the LDP peers are "directly connected" over an
and the label is only going to be used for traffic sent over that interface, and the label is only going to be used for traffic
interface. sent over that interface.
- Per platform label space. Platform-wide incoming labels are used - Per platform label space. Platform-wide incoming labels are
for interfaces that can share the same labels. used for interfaces that can share the same labels.
2.2.2. LDP Identifiers 2.2.2. LDP Identifiers
An LDP identifier is a six octet quantity used to identify an LSR An LDP Identifier is a six octet quantity used to identify an LSR
label space. The first four octets identify the LSR and must be a label space. The first four octets identify the LSR and must be a
globally unique value, such as a 32-bit router Id assigned to the globally unique value, such as a 32-bit router Id assigned to the
LSR. The last two octets identify a specific label space within the LSR. The last two octets identify a specific label space within the
LSR. The last two octets of LDP Identifiers for platform-wide label LSR. The last two octets of LDP Identifiers for platform-wide label
spaces are always both zero. This document uses the following print spaces are always both zero. This document uses the following print
representation for LDP Identifiers: representation for LDP Identifiers:
<LSR Id> : <label space id> <LSR Id> : <label space id>
e.g., lsr171:0, lsr19:2. e.g., lsr171:0, lsr19:2.
skipping to change at page 12, line 23 skipping to change at page 10, line 25
interface labels). Another situation would be where the LSR had two interface labels). Another situation would be where the LSR had two
links to the peer, one of which is ethernet (and uses per platform links to the peer, one of which is ethernet (and uses per platform
labels) and the other of which is ATM. labels) and the other of which is ATM.
2.2.3. LDP Sessions 2.2.3. LDP Sessions
LDP sessions exist between LSRs to support label exchange between LDP sessions exist between LSRs to support label exchange between
them. them.
When an LSR uses LDP to advertise more than one label space to When an LSR uses LDP to advertise more than one label space to
another LSR it uses a separate LDP session for each label space. another LSR, it uses a separate LDP session for each label space.
2.2.4. LDP Transport 2.2.4. LDP Transport
LDP uses TCP as a reliable transport for sessions. LDP uses TCP as a reliable transport for sessions.
When multiple LDP sessions are required between two LSRs there is When multiple LDP sessions are required between two LSRs, there is
one TCP session for each LDP session. one TCP session for each LDP session.
2.3. LDP Sessions between non-Directly Connected LSRs 2.3. LDP Sessions between Non-Directly Connected LSRs
LDP sessions between LSRs that are not directly connected at the link LDP sessions between LSRs that are not directly connected at the link
level may be desirable in some situations. level may be desirable in some situations.
For example, consider a "traffic engineering" application where LSRa For example, consider a "traffic engineering" application where LSRa
sends traffic matching some criteria via an LSP to non-directly con- sends traffic matching some criteria via an LSP to non-directly
nected LSRb rather than forwarding the traffic along its normally connected LSRb rather than forwarding the traffic along its normally
routed path. routed path.
The path between LSRa and LSRb would include one or more intermediate The path between LSRa and LSRb would include one or more intermediate
LSRs (LSR1,...LSRn). An LDP session between LSRa and LSRb would LSRs (LSR1,...LSRn). An LDP session between LSRa and LSRb would
enable LSRb to label switch traffic arriving on the LSP from LSRa by enable LSRb to label switch traffic arriving on the LSP from LSRa by
providing LSRb means to advertise labels for this purpose to LSRa. providing LSRb means to advertise labels for this purpose to LSRa.
In this situation LSRa would apply two labels to traffic it forwards In this situation, LSRa would apply two labels to traffic it forwards
on the LSP to LSRb: a label learned from LSR1 to forward traffic on the LSP to LSRb: a label learned from LSR1 to forward traffic
along the LSP path from LSRa to LSRb; and a label learned from LSRb along the LSP path from LSRa to LSRb; and a label learned from LSRb
to enable LSRb to label switch traffic arriving on the LSP. to enable LSRb to label switch traffic arriving on the LSP.
LSRa first adds the label learned via its LDP session with LSRb to LSRa first adds the label learned via its LDP session with LSRb to
the packet label stack (either by replacing the label on top of the the packet label stack (either by replacing the label on top of the
packet label stack with it if the packet arrives labeled or by push- packet label stack with it if the packet arrives labeled or by
ing it if the packet arrives unlabeled). Next, it pushes the label pushing it if the packet arrives unlabeled). Next, it pushes the
for the LSP learned from LSR1 onto the label stack. label for the LSP learned from LSR1 onto the label stack.
2.4. LDP Discovery 2.4. LDP Discovery
LDP discovery is a mechanism that enables an LSR to discover poten- LDP discovery is a mechanism that enables an LSR to discover
tial LDP peers. Discovery makes it unnecessary to explicitly config- potential LDP peers. Discovery makes it unnecessary to explicitly
ure an LSR's label switching peers. configure an LSR's label switching peers.
There are two variants of the discovery mechanism: There are two variants of the discovery mechanism:
- A basic discovery mechanism used to discover LSR neighbors that - A Basic Discovery mechanism used to discover LSR neighbors that
are directly connected at the link level. are directly connected at the link level.
- An extended discovery mechanism used to locate LSRs that are not - An Extended Discovery mechanism used to locate LSRs that are
directly connected at the link level. not directly connected at the link level.
2.4.1. Basic Discovery Mechanism 2.4.1. Basic Discovery Mechanism
To engage in LDP Basic Discovery on an interface an LSR periodically To engage in LDP Basic Discovery on an interface, an LSR periodically
sends LDP Link Hellos out the interface. LDP Link Hellos are sent as sends LDP Link Hellos out the interface. LDP Link Hellos are sent as
UDP packets addressed to the well-known LDP discovery port for the UDP packets addressed to the well-known LDP discovery port for the
"all routers on this subnet" group multicast address. "all routers on this subnet" group multicast address.
An LDP Link Hello sent by an LSR carries the LDP Identifier for the An LDP Link Hello sent by an LSR carries the LDP Identifier for the
label space the LSR intends to use for the interface and possibly label space the LSR intends to use for the interface and possibly
additional information. additional information.
Receipt of an LDP Link Hello on an interface identifies a "Hello Receipt of an LDP Link Hello on an interface identifies a "Hello
adjacency" with a potential LDP peer reachable at the link level on adjacency" with a potential LDP peer reachable at the link level on
the interface as well as the label space the peer intends to use for the interface as well as the label space the peer intends to use for
the interface. the interface.
2.4.2. Extended Discovery Mechanism 2.4.2. Extended Discovery Mechanism
LDP sessions between non-directly connected LSRs are supported by LDP LDP sessions between non-directly connected LSRs are supported by LDP
Extended Discovery. Extended Discovery.
To engage in LDP Extended Discovery an LSR periodically sends LDP To engage in LDP Extended Discovery, an LSR periodically sends LDP
Targeted Hellos to a specific address. LDP Targeted Hellos are sent Targeted Hellos to a specific address. LDP Targeted Hellos are sent
as UDP packets addressed to the well-known LDP discovery port at the as UDP packets addressed to the well-known LDP discovery port at the
specific address. specific address.
An LDP Targeted Hello sent by an LSR carries the LDP Identifier for An LDP Targeted Hello sent by an LSR carries the LDP Identifier for
the label space the LSR intends to use and possibly additional the label space the LSR intends to use and possibly additional
optional information. optional information.
Extended Discovery differs from Basic Discovery in the following Extended Discovery differs from Basic Discovery in the following
ways: ways:
- A Targeted Hello is sent to a specific address rather than to the - A Targeted Hello is sent to a specific address rather than to
"all routers" group multicast address for the outgoing interface. the "all routers" group multicast address for the outgoing
interface.
- Unlike Basic Discovery, which is symmetric, Extended Discovery is - Unlike Basic Discovery, which is symmetric, Extended Discovery
asymmetric. is asymmetric.
One LSR initiates Extended Discovery with another targeted LSR, One LSR initiates Extended Discovery with another targeted LSR,
and the targeted LSR decides whether to respond to or ignore the and the targeted LSR decides whether to respond to or ignore
Targeted Hello. A targeted LSR that chooses to respond does so the Targeted Hello. A targeted LSR that chooses to respond
by periodically sending Targeted Hellos to the initiating LSR. does so by periodically sending Targeted Hellos to the
initiating LSR.
Receipt of an LDP Targeted Hello identifies a "Hello adjacency" with Receipt of an LDP Targeted Hello identifies a "Hello adjacency" with
a potential LDP peer reachable at the network level and the label a potential LDP peer reachable at the network level and the label
space the peer intends to use. space the peer intends to use.
2.5. Establishing and Maintaining LDP Sessions 2.5. Establishing and Maintaining LDP Sessions
2.5.1. LDP Session Establishment 2.5.1. LDP Session Establishment
The exchange of LDP Discovery Hellos between two LSRs triggers LDP The exchange of LDP Discovery Hellos between two LSRs triggers LDP
session establishment. Session establishment is a two step process: session establishment. Session establishment is a two step process:
- Transport connection establishment. - Transport connection establishment
- Session initialization - Session initialization
The following describes establishment of an LDP session between LSRs The following describes establishment of an LDP session between LSRs
LSR1 and LSR2 from LSR1's point of view. It assumes the exchange of LSR1 and LSR2 from LSR1's point of view. It assumes the exchange of
Hellos specifying label space LSR1:a for LSR1 and label space LSR2:b Hellos specifying label space LSR1:a for LSR1 and label space LSR2:b
for LSR2. for LSR2.
2.5.2. Transport Connection Establishment 2.5.2. Transport Connection Establishment
The exchange of Hellos results in the creation of a Hello adjacency The exchange of Hellos results in the creation of a Hello adjacency
at LSR1 that serves to bind the link (L) and the label spaces LSR1:a at LSR1 that serves to bind the link (L) and the label spaces LSR1:a
and LSR2:b. and LSR2:b.
1. If LSR1 does not already have an LDP session for the exchange of 1. If LSR1 does not already have an LDP session for the exchange
label spaces LSR1:a and LSR2:b it attempts to open a TCP con- of label spaces LSR1:a and LSR2:b, it attempts to open a TCP
nection for a new LDP session with LSR2. connection for a new LDP session with LSR2.
LSR1 determines the transport addresses to be used at its end LSR1 determines the transport addresses to be used at its end
(A1) and LSR2's end (A2) of the LDP TCP connection. Address A1 (A1) and LSR2's end (A2) of the LDP TCP connection. Address A1
is determined as follows: is determined as follows:
a. If LSR1 uses the Transport Address optional object (TLV) in a. If LSR1 uses the Transport Address optional object (TLV) in
Hello's it sends to LSR2 to advertise an address, A1 is the Hellos it sends to LSR2 to advertise an address, A1 is the
address LSR1 advertises via the optional object; address LSR1 advertises via the optional object;
b. If LSR1 does not use the Transport Address optional object, b. If LSR1 does not use the Transport Address optional object,
A1 is the source address used in Hellos it sends to LSR2. A1 is the source address used in Hellos it sends to LSR2.
Similarly, address A2 is determined as follows: Similarly, address A2 is determined as follows:
a. If LSR2 uses the Transport Address optional object, A2 is a. If LSR2 uses the Transport Address optional object, A2 is
the address LSR2 advertises via the optional object; the address LSR2 advertises via the optional object;
b. If LSR2 does not use the Transport Address optional object, b. If LSR2 does not use the Transport Address optional object,
A2 is the source address in Hellos received from LSR2. A2 is the source address in Hellos received from LSR2.
2. LSR1 determines whether it will play the active or passive role 2. LSR1 determines whether it will play the active or passive role
in session establishment by comparing addresses A1 and A2 as in session establishment by comparing addresses A1 and A2 as
unsigned integers. If A1 > A2, LSR1 plays the active role; unsigned integers. If A1 > A2, LSR1 plays the active role;
otherwise it is passive. otherwise, it is passive.
The procedure for comparing A1 and A2 as unsigned integers is: The procedure for comparing A1 and A2 as unsigned integers is:
- If A1 and A2 are not in the same address family, they are - If A1 and A2 are not in the same address family, they are
incomparable, and no session can be established. incomparable, and no session can be established.
- Let U1 be the abstract unsigned integer obtained by treat- - Let U1 be the abstract unsigned integer obtained by treating
ing A1 as a sequence of bytes, where the byte which appears A1 as a sequence of bytes, where the byte that appears
earliest in the message is the most significant byte of the earliest in the message is the most significant byte of the
integer and the byte which appears latest in the message is integer and the byte that appears latest in the message is
the least significant byte of the integer. the least significant byte of the integer.
Let U2 be the abstract unsigned integer obtained from A2 in Let U2 be the abstract unsigned integer obtained from A2 in
a similar manner. a similar manner.
- Compare U1 with U2. If U1 > U2, then A1 > A2; if U1 < U2, - Compare U1 with U2. If U1 > U2, then A1 > A2; if U1 < U2,
then A1 < A2. then A1 < A2.
3. If LSR1 is active, it attempts to establish the LDP TCP connec- 3. If LSR1 is active, it attempts to establish the LDP TCP
tion by connecting to the well-known LDP port at address A2. connection by connecting to the well-known LDP port at address
If LSR1 is passive, it waits for LSR2 to establish the LDP TCP A2. If LSR1 is passive, it waits for LSR2 to establish the LDP
connection to its well-known LDP port. TCP connection to its well-known LDP port.
Note that when an LSR sends a Hello it selects the transport address Note that when an LSR sends a Hello, it selects the transport address
for its end of the session connection and uses the Hello to advertise for its end of the session connection and uses the Hello to advertise
the address, either explicitly by including it in an optional Trans- the address, either explicitly by including it in an optional
port Address TLV or implicitly by omitting the TLV and using it as Transport Address TLV or implicitly by omitting the TLV and using it
the Hello source address. as the Hello source address.
An LSR MUST advertise the same transport address in all Hellos that An LSR MUST advertise the same transport address in all Hellos that
advertise the same label space. This requirement ensures that two advertise the same label space. This requirement ensures that two
LSRs linked by multiple Hello adjacencies using the same label spaces LSRs linked by multiple Hello adjacencies using the same label spaces
play the same connection establishment role for each adjacency. play the same connection establishment role for each adjacency.
2.5.3. Session Initialization 2.5.3. Session Initialization
After LSR1 and LSR2 establish a transport connection they negotiate After LSR1 and LSR2 establish a transport connection, they negotiate
session parameters by exchanging LDP Initialization messages. The session parameters by exchanging LDP Initialization messages. The
parameters negotiated include LDP protocol version, label distribu- parameters negotiated include LDP protocol version, label
tion method, timer values, VPI/VCI (Virtual Path Identifier/ Virtual distribution method, timer values, VPI/VCI (Virtual Path Identifier /
Channel Identifier) ranges for label controlled ATM, DLCI (Data Link Virtual Channel Identifier) ranges for label controlled ATM, DLCI
Connection Identifier) ranges for label controlled Frame Relay, etc. (Data Link Connection Identifier) ranges for label controlled Frame
Relay, etc.
Successful negotiation completes establishment of an LDP session Successful negotiation completes establishment of an LDP session
between LSR1 and LSR2 for the advertisement of label spaces LSR1:a between LSR1 and LSR2 for the advertisement of label spaces LSR1:a
and LSR2:b. and LSR2:b.
The following describes the session initialization from LSR1's point The following describes the session initialization from LSR1's point
of view. of view.
After the connection is established, if LSR1 is playing the active After the connection is established, if LSR1 is playing the active
role, it initiates negotiation of session parameters by sending an role, it initiates negotiation of session parameters by sending an
Initialization message to LSR2. If LSR1 is passive, it waits for Initialization message to LSR2. If LSR1 is passive, it waits for
LSR2 to initiate the parameter negotiation. LSR2 to initiate the parameter negotiation.
In general when there are multiple links between LSR1 and LSR2 and In general when there are multiple links between LSR1 and LSR2 and
multiple label spaces to be advertised by each, the passive LSR can- multiple label spaces to be advertised by each, the passive LSR
not know which label space to advertise over a newly established TCP cannot know which label space to advertise over a newly established
connection until it receives the LDP Initialization message on the TCP connection until it receives the LDP Initialization message on
connection. The Initialization message carries both the LDP Identi- the connection. The Initialization message carries both the LDP
fier for the sender's (active LSR's) label space and the LDP Identi- Identifier for the sender's (active LSR's) label space and the LDP
fier for the receiver's (passive LSR's) label space. Identifier for the receiver's (passive LSR's) label space.
By waiting for the Initialization message from its peer the passive By waiting for the Initialization message from its peer, the passive
LSR can match the label space to be advertised by the peer (as deter- LSR can match the label space to be advertised by the peer (as
mined from the LDP Identifier in the PDU header for the Initializa- determined from the LDP Identifier in the PDU header for the
tion message) with a Hello adjacency previously created when Hellos Initialization message) with a Hello adjacency previously created
were exchanged. when Hellos were exchanged.
1. When LSR1 plays the passive role: 1. When LSR1 plays the passive role:
a. If LSR1 receives an Initialization message it attempts to a. If LSR1 receives an Initialization message, it attempts to
match the LDP Identifier carried by the message PDU with a match the LDP Identifier carried by the message PDU with a
Hello adjacency. Hello adjacency.
b. If there is a matching Hello adjacency, the adjacency speci- b. If there is a matching Hello adjacency, the adjacency
fies the local label space for the session. specifies the local label space for the session.
Next LSR1 checks whether the session parameters proposed in Next LSR1 checks whether the session parameters proposed in
the message are acceptable. If they are, LSR1 replies with the message are acceptable. If they are, LSR1 replies with
an Initialization message of its own to propose the parame- an Initialization message of its own to propose the
ters it wishes to use and a KeepAlive message to signal parameters it wishes to use and a KeepAlive message to
acceptance of LSR2's parameters. If the parameters are not signal acceptance of LSR2's parameters. If the parameters
acceptable, LSR1 responds by sending a Session are not acceptable, LSR1 responds by sending a Session
Rejected/Parameters Error Notification message and closing Rejected/Parameters Error Notification message and closing
the TCP connection. the TCP connection.
c. If LSR1 cannot find a matching Hello adjacency it sends a c. If LSR1 cannot find a matching Hello adjacency, it sends a
Session Rejected/No Hello Error Notification message and Session Rejected/No Hello Error Notification message and
closes the TCP connection. closes the TCP connection.
d. If LSR1 receives a KeepAlive in response to its Initializa- d. If LSR1 receives a KeepAlive in response to its
tion message, the session is operational from LSR1's point Initialization message, the session is operational from
of view. LSR1's point of view.
e. If LSR1 receives an Error Notification message, LSR2 has e. If LSR1 receives an Error Notification message, LSR2 has
rejected its proposed session and LSR1 closes the TCP con- rejected its proposed session and LSR1 closes the TCP
nection. connection.
2. When LSR1 plays the active role: 2. When LSR1 plays the active role:
a. If LSR1 receives an Error Notification message, LSR2 has a. If LSR1 receives an Error Notification message, LSR2 has
rejected its proposed session and LSR1 closes the TCP con- rejected its proposed session and LSR1 closes the TCP
nection. connection.
b. If LSR1 receives an Initialization message, it checks b. If LSR1 receives an Initialization message, it checks
whether the session parameters are acceptable. If so, it whether the session parameters are acceptable. If so, it
replies with a KeepAlive message. If the session parame- replies with a KeepAlive message. If the session parameters
ters are unacceptable, LSR1 sends a Session Rejected/Param- are unacceptable, LSR1 sends a Session Rejected/Parameters
eters Error Notification message and closes the connection. Error Notification message and closes the connection.
c. If LSR1 receives a KeepAlive message, LSR2 has accepted its c. If LSR1 receives a KeepAlive message, LSR2 has accepted its
proposed session parameters. proposed session parameters.
d. When LSR1 has received both an acceptable Initialization d. When LSR1 has received both an acceptable Initialization
message and a KeepAlive message the session is operational message and a KeepAlive message, the session is operational
from LSR1's point of view. from LSR1's point of view.
Until the LDP session is established, no other messages Until the LDP session is established, no other messages
except those listed in the procedures above may be except those listed in the procedures above may be
exchanged, and the rules for processing the U-bit in LDP exchanged, and the rules for processing the U-bit in LDP
messages are overridden. If a message other than those messages are overridden. If a message other than those
listed in the procedures above is received, a Shutdown msg listed in the procedures above is received, a Shutdown msg
MUST be transmitted and the transport connection MUST be MUST be transmitted and the transport connection MUST be
closed. closed.
It is possible for a pair of incompatibly configured LSRs that It is possible for a pair of incompatibly configured LSRs that
disagree on session parameters to engage in an endless sequence disagree on session parameters to engage in an endless sequence of
of messages as each NAKs the other's Initialization messages with messages as each NAKs the other's Initialization messages with Error
Error Notification messages. Notification messages.
An LSR MUST throttle its session setup retry attempts with an An LSR MUST throttle its session setup retry attempts with an
exponential backoff in situations where Initialization messages exponential backoff in situations where Initialization messages are
are being NAK'd. It is also recommended that an LSR detecting being NAK'd. It is also recommended that an LSR detecting such a
such a situation take action to notify an operator. situation take action to notify an operator.
The session establishment setup attempt following a NAK'd Ini- The session establishment setup attempt following a NAK'd
tialization message MUST be delayed no less than 15 seconds, and Initialization message MUST be delayed no less than 15 seconds, and
subsequent delays MUST grow to a maximum delay of no less than 2 subsequent delays MUST grow to a maximum delay of no less than 2
minutes. The specific session establishment action that must be minutes. The specific session establishment action that must be
delayed is the attempt to open the session transport connection delayed is the attempt to open the session transport connection by
by the LSR playing the active role. the LSR playing the active role.
The throttled sequence of Initialization NAKs is unlikely to The throttled sequence of Initialization NAKs is unlikely to cease
cease until operator intervention reconfigures one of the LSRs. until operator intervention reconfigures one of the LSRs. After such
After such a configuration action there is no further need to a configuration action, there is no further need to throttle
throttle subsequent session establishment attempts (until their subsequent session establishment attempts (until their Initialization
initialization messages are NAK'd). messages are NAK'd).
Due to the asymmetric nature of session establishment, reconfigu- Due to the asymmetric nature of session establishment,
ration of the passive LSR will go unnoticed by the active LSR reconfiguration of the passive LSR will go unnoticed by the active
without some further action. Section "Hello Message" describes LSR without some further action. Section "Hello Message" describes
an optional mechanism an LSR can use to signal potential LDP an optional mechanism an LSR can use to signal potential LDP peers
peers that it has been reconfigured. that it has been reconfigured.
2.5.4. Initialization State Machine 2.5.4. Initialization State Machine
It is convenient to describe LDP session negotiation behavior in It is convenient to describe LDP session negotiation behavior in
terms of a state machine. We define the LDP state machine to have terms of a state machine. We define the LDP state machine to have
five possible states and present the behavior as a state transition five possible states and present the behavior as a state transition
table and as a state transition diagram. Note that a shutdown message table and as a state transition diagram. Note that a Shutdown
is implemented as a notification message with a status TLV indicating message is implemented as a Notification message with a Status TLV
a fatal error. indicating a fatal error.
Session Initialization State Transition Table Session Initialization State Transition Table
STATE EVENT NEW STATE STATE EVENT NEW STATE
NON EXISTENT Session TCP connection established INITIALIZED NON EXISTENT Session TCP connection established INITIALIZED
established established
INITIALIZED Transmit Initialization msg OPENSENT INITIALIZED Transmit Initialization msg OPENSENT
(Active Role) (Active Role)
skipping to change at page 21, line 11 skipping to change at page 19, line 11
LDP msgs | | Tx Shutdown msg LDP msgs | | Tx Shutdown msg
| | | |
+---+ +---+
2.5.5. Maintaining Hello Adjacencies 2.5.5. Maintaining Hello Adjacencies
An LDP session with a peer has one or more Hello adjacencies. An LDP session with a peer has one or more Hello adjacencies.
An LDP session has multiple Hello adjacencies when a pair of LSRs is An LDP session has multiple Hello adjacencies when a pair of LSRs is
connected by multiple links that share the same label space; for connected by multiple links that share the same label space; for
example, multiple PPP links between a pair of routers. In this situ- example, multiple PPP links between a pair of routers. In this
ation the Hellos an LSR sends on each such link carry the same LDP situation, the Hellos an LSR sends on each such link carry the same
Identifier. LDP Identifier.
LDP includes mechanisms to monitor the necessity of an LDP session LDP includes mechanisms to monitor the necessity of an LDP session
and its Hello adjacencies. and its Hello adjacencies.
LDP uses the regular receipt of LDP Discovery Hellos to indicate a LDP uses the regular receipt of LDP Discovery Hellos to indicate a
peer's intent to use the label space identified by the Hello. An LSR peer's intent to use the label space identified by the Hello. An LSR
maintains a hold timer with each Hello adjacency which it restarts maintains a hold timer with each Hello adjacency that it restarts
when it receives a Hello that matches the adjacency. If the timer when it receives a Hello that matches the adjacency. If the timer
expires without receipt of a matching Hello from the peer, LDP con- expires without receipt of a matching Hello from the peer, LDP
cludes that the peer no longer wishes to label switch using that concludes that the peer no longer wishes to label switch using that
label space for that link (or target, in the case of Targeted Hellos) label space for that link (or target, in the case of Targeted Hellos)
or that the peer has failed. The LSR then deletes the Hello adja- or that the peer has failed. The LSR then deletes the Hello
cency. When the last Hello adjacency for a LDP session is deleted, adjacency. When the last Hello adjacency for an LDP session is
the LSR terminates the LDP session by sending a Notification message deleted, the LSR terminates the LDP session by sending a Notification
and closing the transport connection. message and closing the transport connection.
2.5.6. Maintaining LDP Sessions 2.5.6. Maintaining LDP Sessions
LDP includes mechanisms to monitor the integrity of the LDP session. LDP includes mechanisms to monitor the integrity of the LDP session.
LDP uses the regular receipt of LDP PDUs on the session transport LDP uses the regular receipt of LDP PDUs on the session transport
connection to monitor the integrity of the session. An LSR maintains connection to monitor the integrity of the session. An LSR maintains
a KeepAlive timer for each peer session which it resets whenever it a KeepAlive Timer for each peer session that it resets whenever it
receives an LDP PDU from the session peer. If the KeepAlive timer receives an LDP PDU from the session peer. If the KeepAlive Timer
expires without receipt of an LDP PDU from the peer the LSR concludes expires without receipt of an LDP PDU from the peer, the LSR
that the transport connection is bad or that the peer has failed, and concludes that the transport connection is bad or that the peer has
it terminates the LDP session by closing the transport connection. failed, and it terminates the LDP session by closing the transport
connection.
After an LDP session has been established, an LSR must arrange that After an LDP session has been established, an LSR must arrange that
its peer receive an LDP PDU from it at least every KeepAlive time its peer receive an LDP PDU from it at least every KeepAlive time
period to ensure the peer restarts the session KeepAlive timer. The period to ensure the peer restarts the session KeepAlive Timer. The
LSR may send any protocol message to meet this requirement. In cir- LSR may send any protocol message to meet this requirement. In
cumstances where an LSR has no other information to communicate to circumstances where an LSR has no other information to communicate to
its peer, it sends a KeepAlive message. its peer, it sends a KeepAlive message.
An LSR may choose to terminate an LDP session with a peer at any An LSR may choose to terminate an LDP session with a peer at any
time. Should it choose to do so, it informs the peer with a Shutdown time. Should it choose to do so, it informs the peer with a Shutdown
message. message.
2.6. Label Distribution and Management 2.6. Label Distribution and Management
The MPLS architecture [RFC3031] allows an LSR to distribute a FEC The MPLS architecture [RFC3031] allows an LSR to distribute a FEC
label binding in response to an explicit request from another LSR. label binding in response to an explicit request from another LSR.
This is known as Downstream On Demand label distribution. It also This is known as Downstream On Demand label distribution. It also
allows an LSR to distribute label bindings to LSRs that have not allows an LSR to distribute label bindings to LSRs that have not
explicitly requested them. [RFC3031] calls this method of label dis- explicitly requested them. [RFC3031] calls this method of label
tribution Unsolicited Downstream; this document uses the term Down- distribution Unsolicited Downstream; this document uses the term
stream Unsolicited. Downstream Unsolicited.
Both of these label distribution techniques may be used in the same Both of these label distribution techniques may be used in the same
network at the same time. However, for any given LDP session, each network at the same time. However, for any given LDP session, each
LSR must be aware of the label distribution method used by its peer LSR must be aware of the label distribution method used by its peer
in order to avoid situations where one peer using Downstream Unso- in order to avoid situations where one peer using Downstream
licited label distribution assumes its peer is also. See Section Unsolicited label distribution assumes its peer is also. See Section
"Downstream on Demand label Advertisement". "Downstream on Demand Label Advertisement".
2.6.1. Label Distribution Control Mode 2.6.1. Label Distribution Control Mode
The behavior of the initial setup of LSPs is determined by whether The behavior of the initial setup of LSPs is determined by whether
the LSR is operating with independent or ordered LSP control. An LSR the LSR is operating with independent or Ordered LSP Control. An LSR
may support both types of control as a configurable option. may support both types of control as a configurable option.
2.6.1.1. Independent Label Distribution Control 2.6.1.1. Independent Label Distribution Control
When using independent LSP control, each LSR may advertise label map- When using independent LSP control, each LSR may advertise label
pings to its neighbors at any time it desires. For example, when mappings to its neighbors at any time it desires. For example, when
operating in independent Downstream on Demand mode, an LSR may answer operating in independent Downstream on Demand mode, an LSR may answer
requests for label mappings immediately, without waiting for a label requests for label mappings immediately, without waiting for a label
mapping from the next hop. When operating in independent Downstream mapping from the next hop. When operating in independent Downstream
Unsolicited mode, an LSR may advertise a label mapping for a FEC to Unsolicited mode, an LSR may advertise a label mapping for a FEC to
its neighbors whenever it is prepared to label-switch that FEC. its neighbors whenever it is prepared to label-switch that FEC.
A consequence of using independent mode is that an upstream label can A consequence of using independent mode is that an upstream label can
be advertised before a downstream label is received. be advertised before a downstream label is received.
2.6.1.2. Ordered Label Distribution Control 2.6.1.2. Ordered Label Distribution Control
When using LSP ordered control, an LSR may initiate the transmission When using LSP Ordered Control, an LSR may initiate the transmission
of a label mapping only for a FEC for which it has a label mapping of a label mapping only for a FEC for which it has a label mapping
for the FEC next hop, or for which the LSR is the egress. For each for the FEC next hop, or for which the LSR is the egress. For each
FEC for which the LSR is not the egress and no mapping exists, the FEC for which the LSR is not the egress and no mapping exists, the
LSR MUST wait until a label from a downstream LSR is received before LSR MUST wait until a label from a downstream LSR is received before
mapping the FEC and passing corresponding labels to upstream LSRs. mapping the FEC and passing corresponding labels to upstream LSRs.
An LSR may be an egress for some FECs and a non-egress for others. An LSR may be an egress for some FECs and a non-egress for others.
An LSR may act as an egress LSR, with respect to a particular FEC, An LSR may act as an egress LSR, with respect to a particular FEC,
under any of the following conditions: under any of the following conditions:
1. The FEC refers to the LSR itself (including one of its directly 1. The FEC refers to the LSR itself (including one of its directly
attached interfaces). attached interfaces).
2. The next hop router for the FEC is outside of the Label Switch- 2. The next hop router for the FEC is outside of the Label
ing Network. Switching Network.
3. FEC elements are reachable by crossing a routing domain bound- 3. FEC elements are reachable by crossing a routing domain
ary, such as another area for OSPF summary networks, or another boundary, such as another area for OSPF summary networks, or
autonomous system for OSPF AS externals and BGP routes another autonomous system for OSPF AS externals and BGP routes
[RFC2328] [RFC4271]. [RFC2328] [RFC4271].
Note that whether an LSR is an egress for a given FEC may change over Note that whether an LSR is an egress for a given FEC may change over
time, depending on the state of the network and LSR configuration time, depending on the state of the network and LSR configuration
settings. settings.
2.6.2. Label Retention Mode 2.6.2. Label Retention Mode
The MPLS architecture [RFC3031] introduces the notion of label reten- The MPLS architecture [RFC3031] introduces the notion of label
tion mode which specifies whether an LSR maintains a label binding retention mode which specifies whether an LSR maintains a label
for a FEC learned from a neighbor that is not its next hop for the binding for a FEC learned from a neighbor that is not its next hop
FEC. for the FEC.
2.6.2.1. Conservative Label Retention Mode 2.6.2.1. Conservative Label Retention Mode
In Downstream Unsolicited advertisement mode, label mapping adver- In Downstream Unsolicited advertisement mode, label mapping
tisements for all routes may be received from all peer LSRs. When advertisements for all routes may be received from all peer LSRs.
using conservative label retention, advertised label mappings are When using Conservative Label retention, advertised label mappings
retained only if they will be used to forward packets (i.e., if they are retained only if they will be used to forward packets (i.e., if
are received from a valid next hop according to routing). If operat- they are received from a valid next hop according to routing). If
ing in Downstream on Demand mode, an LSR will request label mappings operating in Downstream on Demand mode, an LSR will request label
only from the next hop LSR according to routing. Since Downstream on mappings only from the next hop LSR according to routing. Since
Demand mode is primarily used when label conservation is desired Downstream on Demand mode is primarily used when label conservation
(e.g., an ATM switch with limited cross connect space), it is typi- is desired (e.g., an ATM switch with limited cross connect space), it
cally used with the conservative label retention mode. is typically used with the Conservative Label retention mode.
The main advantage of the conservative mode is that only the labels The main advantage of the conservative mode is that only the labels
that are required for the forwarding of data are allocated and main- that are required for the forwarding of data are allocated and
tained. This is particularly important in LSRs where the label space maintained. This is particularly important in LSRs where the label
is inherently limited, such as in an ATM switch. A disadvantage of space is inherently limited, such as in an ATM switch. A
the conservative mode is that if routing changes the next hop for a disadvantage of the conservative mode is that if routing changes the
given destination, a new label must be obtained from the new next hop next hop for a given destination, a new label must be obtained from
before labeled packets can be forwarded. the new next hop before labeled packets can be forwarded.
2.6.2.2. Liberal Label Retention Mode 2.6.2.2. Liberal Label Retention Mode
In Downstream Unsolicited advertisement mode, label mapping adver- In Downstream Unsolicited advertisement mode, label mapping
tisements for all routes may be received from all LDP peers. When advertisements for all routes may be received from all LDP peers.
using liberal label retention, every label mappings received from a When using Liberal Label retention, every label mappings received
peer LSR is retained regardless of whether the LSR is the next hop from a peer LSR is retained regardless of whether the LSR is the next
for the advertised mapping. When operating in Downstream on Demand hop for the advertised mapping. When operating in Downstream on
mode with liberal label retention, an LSR might choose to request Demand mode with Liberal Label retention, an LSR might choose to
label mappings for all known prefixes from all peer LSRs. Note, how- request label mappings for all known prefixes from all peer LSRs.
ever, that Downstream on Demand mode is typically used by devices Note, however, that Downstream on Demand mode is typically used by
such as ATM switch-based LSRs for which the conservative approach is devices such as ATM switch-based LSRs for which the conservative
recommended. approach is recommended.
The main advantage of the liberal label retention mode is that reac- The main advantage of the Liberal Label retention mode is that
tion to routing changes can be quick because labels already exist. reaction to routing changes can be quick because labels already
The main disadvantage of the liberal mode is that unneeded label map- exist. The main disadvantage of the liberal mode is that unneeded
pings are distributed and maintained. label mappings are distributed and maintained.
2.6.3. Label Advertisement Mode 2.6.3. Label Advertisement Mode
Each interface on an LSR is configured to operate in either Down- Each interface on an LSR is configured to operate in either
stream Unsolicited or Downstream on Demand advertisement mode. LSRs Downstream Unsolicited or Downstream on Demand advertisement mode.
exchange advertisement modes during initialization. The major dif- LSRs exchange advertisement modes during initialization. The major
ference between Downstream Unsolicited and Downstream on Demand modes difference between Downstream Unsolicited and Downstream on Demand
is in which LSR takes responsibility for initiating mapping requests modes is in which LSR takes responsibility for initiating mapping
and mapping advertisements. requests and mapping advertisements.
2.7. LDP Identifiers and Next Hop Addresses 2.7. LDP Identifiers and Next Hop Addresses
An LSR maintains learned labels in a Label Information Base (LIB). An LSR maintains learned labels in a Label Information Base (LIB).
When operating in Downstream Unsolicited mode, the LIB entry for an When operating in Downstream Unsolicited mode, the LIB entry for an
address prefix associates a collection of (LDP Identifier, label) address prefix associates a collection of (LDP Identifier, label)
pairs with the prefix, one such pair for each peer advertising a pairs with the prefix, one such pair for each peer advertising a
label for the prefix. label for the prefix.
When the next hop for a prefix changes the LSR must retrieve the When the next hop for a prefix changes, the LSR must retrieve the
label advertised by the new next hop from the LIB for use in forward- label advertised by the new next hop from the LIB for use in
ing. To retrieve the label the LSR must be able to map the next hop forwarding. To retrieve the label, the LSR must be able to map the
address for the prefix to an LDP Identifier. next hop address for the prefix to an LDP Identifier.
Similarly, when the LSR learns a label for a prefix from an LDP peer, Similarly, when the LSR learns a label for a prefix from an LDP peer,
it must be able to determine whether that peer is currently a next it must be able to determine whether that peer is currently a next
hop for the prefix to determine whether it needs to start using the hop for the prefix to determine whether it needs to start using the
newly learned label when forwarding packets that match the prefix. newly learned label when forwarding packets that match the prefix.
To make that decision the LSR must be able to map an LDP Identifier To make that decision, the LSR must be able to map an LDP Identifier
to the peer's addresses to check whether any are a next hop for the to the peer's addresses to check whether any are a next hop for the
prefix. prefix.
To enable LSRs to map between a peer LDP identifier and the peer's To enable LSRs to map between a peer LDP Identifier and the peer's
addresses, LSRs advertise their addresses using LDP Address and With- addresses, LSRs advertise their addresses using LDP Address and
draw Address messages. Withdraw Address messages.
An LSR sends an Address message to advertise its addresses to a peer. An LSR sends an Address message to advertise its addresses to a peer.
An LSR sends a Withdraw Address message to withdraw previously adver- An LSR sends a Withdraw Address message to withdraw previously
tised addresses from a peer advertised addresses from a peer.
2.8. Loop Detection 2.8. Loop Detection
Loop detection is a configurable option which provides a mechanism Loop Detection is a configurable option that provides a mechanism for
for finding looping LSPs and for preventing Label Request messages finding looping LSPs and for preventing Label Request messages from
from looping in the presence of non-merge capable LSRs. looping in the presence of non-merge capable LSRs.
The mechanism makes use of Path Vector and Hop Count TLVs carried by The mechanism makes use of Path Vector and Hop Count TLVs carried by
Label Request and Label Mapping messages. It builds on the following Label Request and Label Mapping messages. It builds on the following
basic properties of these TLVs: basic properties of these TLVs:
- A Path Vector TLV contains a list of the LSRs that its containing - A Path Vector TLV contains a list of the LSRs that its
message has traversed. An LSR is identified in a Path Vector containing message has traversed. An LSR is identified in a
list by its unique LSR Identifier (Id), which is the first four Path Vector list by its unique LSR Identifier (Id), which is
octets of its LDP Identifier. When an LSR propagates a message the first four octets of its LDP Identifier. When an LSR
containing a Path Vector TLV it adds its LSR Id to the Path Vec- propagates a message containing a Path Vector TLV, it adds its
tor list. An LSR that receives a message with a Path Vector that LSR Id to the Path Vector list. An LSR that receives a message
contains its LSR Id detects that the message has traversed a with a Path Vector that contains its LSR Id detects that the
loop. LDP supports the notion of a maximum allowable Path Vector message has traversed a loop. LDP supports the notion of a
length; an LSR that detects a Path Vector has reached the maximum maximum allowable Path Vector length; an LSR that detects a
length behaves as if the containing message has traversed a loop. Path Vector has reached the maximum length behaves as if the
containing message has traversed a loop.
- A Hop Count TLV contains a count of the LSRS that the containing - A Hop Count TLV contains a count of the LSRS that the
message has traversed. When an LSR propagates a message contain- containing message has traversed. When an LSR propagates a
ing a Hop Count TLV it increments the count. An LSR that detects message containing a Hop Count TLV, it increments the count.
a Hop Count has reached a configured maximum value behaves as if An LSR that detects a Hop Count has reached a configured
the containing message has traversed a loop. By convention a maximum value behaves as if the containing message has
count of 0 is interpreted to mean the hop count is unknown. traversed a loop. By convention, a count of 0 is interpreted
Incrementing an unknown hop count value results in an unknown hop to mean the hop count is unknown. Incrementing an unknown hop
count value (0). count value results in an unknown hop count value (0).
The following paragraphs describes LDP loop detection procedures. The following paragraphs describe LDP Loop Detection procedures. For
For these paragraphs, and only these paragraphs, "MUST" is redefined these paragraphs, and only these paragraphs, "MUST" is redefined to
to mean "MUST if configured for loop detection". The paragraphs mean "MUST if configured for Loop Detection". The paragraphs specify
specify messages that MUST carry Path Vector and Hop Count TLVs. messages that MUST carry Path Vector and Hop Count TLVs. Note that
Note that the Hop Count TLV and its procedures are used without the the Hop Count TLV and its procedures are used without the Path Vector
Path Vector TLV in situations when loop detection is not configured TLV in situations when Loop Detection is not configured (see
(see [RFC3035] and [RFC3034]). [RFC3035] and [RFC3034]).
2.8.1. Label Request Message 2.8.1. Label Request Message
The use of the Path Vector TLV and Hop Count TLV prevent Label The use of the Path Vector TLV and Hop Count TLV prevent Label
Request messages from looping in environments that include non-merge Request messages from looping in environments that include non-merge
capable LSRs. capable LSRs.
The rules that govern use of the Hop Count TLV in Label Request mes- The rules that govern use of the Hop Count TLV in Label Request
sages by LSR R when Loop Detection is enabled are the following: messages by LSR R when Loop Detection is enabled are the following:
- The Label Request message MUST include a Hop Count TLV. - The Label Request message MUST include a Hop Count TLV.
- If R is sending the Label Request because it is a FEC ingress, it - If R is sending the Label Request because it is a FEC ingress, it
MUST include a Hop Count TLV with hop count value 1. MUST include a Hop Count TLV with hop count value 1.
- If R is sending the Label Request as a result of having received a - If R is sending the Label Request as a result of having received a
Label Request from an upstream LSR, and if the received Label Label Request from an upstream LSR, and if the received Label
Request contains a Hop Count TLV, R MUST increment the received hop Request contains a Hop Count TLV, R MUST increment the received
count value by 1 and MUST pass the resulting value in a Hop Count hop count value by 1 and MUST pass the resulting value in a Hop
TLV to its next hop along with the Label Request message; Count TLV to its next hop along with the Label Request message.
The rules that govern use of the Path Vector TLV in Label Request The rules that govern use of the Path Vector TLV in Label Request
messages by LSR R when Loop Detection is enabled are the following: messages by LSR R when Loop Detection is enabled are the following:
- If R is sending the Label Request because it is a FEC ingress, - If R is sending the Label Request because it is a FEC ingress,
then if R is non-merge capable, it MUST include a Path Vector TLV then if R is non-merge capable, it MUST include a Path Vector TLV
of length 1 containing its own LSR Id. of length 1 containing its own LSR Id.
- If R is sending the Label Request as a result of having received - If R is sending the Label Request as a result of having received a
a Label Request from an upstream LSR, then if the received Label Label Request from an upstream LSR, then if the received Label
Request contains a Path Vector TLV or if R is non-merge capable: Request contains a Path Vector TLV or if R is non-merge capable:
R MUST add its own LSR Id to the Path Vector, and MUST pass R MUST add its own LSR Id to the Path Vector, and MUST pass the
the resulting Path Vector to its next hop along with the resulting Path Vector to its next hop along with the Label
Label Request message. If the Label Request contains no Path Request message. If the Label Request contains no Path Vector
Vector TLV, R MUST include a Path Vector TLV of length 1 con- TLV, R MUST include a Path Vector TLV of length 1 containing
taining its own LSR Id. its own LSR Id.
Note that if R receives a Label Request message for a particular Note that if R receives a Label Request message for a particular FEC,
FEC, and R has previously sent a Label Request message for that FEC and R has previously sent a Label Request message for that FEC to its
to its next hop and has not yet received a reply, and if R intends next hop and has not yet received a reply, and if R intends to merge
to merge the newly received Label Request with the existing out- the newly received Label Request with the existing outstanding Label
standing Label Request, then R does not propagate the Label Request Request, then R does not propagate the Label Request to the next hop.
to the next hop.
If R receives a Label Request message from its next hop with a Hop If R receives a Label Request message from its next hop with a Hop
Count TLV which exceeds the configured maximum value, or with a Count TLV that exceeds the configured maximum value, or with a Path
Path Vector TLV containing its own LSR Id or which exceeds the max- Vector TLV containing its own LSR Id or which exceeds the maximum
imum allowable length, then R detects that the Label Request allowable length, then R detects that the Label Request message has
message has traveled in a loop. traveled in a loop.
When R detects a loop, it MUST send a Loop Detected Notification When R detects a loop, it MUST send a Loop Detected Notification
message to the source of the Label Request message and drop the message to the source of the Label Request message and drop the Label
Label Request message. Request message.
2.8.2. Label Mapping Message 2.8.2. Label Mapping Message
The use of the Path Vector TLV and Hop Count TLV in the Label Mapping The use of the Path Vector TLV and Hop Count TLV in the Label Mapping
message provide a mechanism to find and terminate looping LSPs. When message provide a mechanism to find and terminate looping LSPs. When
an LSR receives a Label Mapping message from a next hop, the message an LSR receives a Label Mapping message from a next hop, the message
is propagated upstream as specified below until an ingress LSR is is propagated upstream as specified below until an ingress LSR is
reached or a loop is found. reached or a loop is found.
The rules that govern the use of the Hop Count TLV in Label Mapping The rules that govern the use of the Hop Count TLV in Label Mapping
messages sent by an LSR R when Loop Detection is enabled are the fol- messages sent by an LSR R when Loop Detection is enabled are the
lowing: following:
- R MUST include a Hop Count TLV. - R MUST include a Hop Count TLV.
- If R is the egress, the hop count value MUST be 1. - If R is the egress, the hop count value MUST be 1.
- If the Label Mapping message is being sent to propagate a Label - If the Label Mapping message is being sent to propagate a Label
Mapping message received from the next hop to an upstream peer, the Mapping message received from the next hop to an upstream peer,
hop count value MUST be determined as follows: the hop count value MUST be determined as follows:
o If R is a member of the edge set of an LSR domain whose LSRs do o If R is a member of the edge set of an LSR domain whose LSRs do
not perform 'TTL-decrement' (e.g., an ATM LSR domain or a Frame not perform 'TTL-decrement' (e.g., an ATM LSR domain or a Frame
Relay LSR domain) and the upstream peer is within that domain, R Relay LSR domain) and the upstream peer is within that domain,
MUST reset the hop count to 1 before propagating the message. R MUST reset the hop count to 1 before propagating the message.
o Otherwise, R MUST increment the hop count received from the next o Otherwise, R MUST increment the hop count received from the
hop before propagating the message. next hop before propagating the message.
- If the Label Mapping message is not being sent to propagate a - If the Label Mapping message is not being sent to propagate a
Label Mapping message, the hop count value MUST be the result of Label Mapping message, the hop count value MUST be the result of
incrementing R's current knowledge of the hop count learned from incrementing R's current knowledge of the hop count learned from
previous Label Mapping messages. Note that this hop count value previous Label Mapping messages. Note that this hop count value
will be unknown if R has not received a Label Mapping message from will be unknown if R has not received a Label Mapping message from
the next hop. the next hop.
Any Label Mapping message MAY contain a Path Vector TLV. The rules Any Label Mapping message MAY contain a Path Vector TLV. The rules
that govern the mandatory use of the Path Vector TLV in Label Mapping that govern the mandatory use of the Path Vector TLV in Label Mapping
messages sent by LSR R when Loop Detection is enabled are the follow- messages sent by LSR R when Loop Detection is enabled are the
ing: following:
- If R is the egress, the Label Mapping message need not include a - If R is the egress, the Label Mapping message need not include a
Path Vector TLV. Path Vector TLV.
- If R is sending the Label Mapping message to propagate a Label - If R is sending the Label Mapping message to propagate a Label
Mapping message received from the next hop to an upstream peer, Mapping message received from the next hop to an upstream peer,
then: then:
o If R is merge capable and if R has not previously sent a Label o If R is merge capable and if R has not previously sent a Label
Mapping message to the upstream peer, then it MUST include a Mapping message to the upstream peer, then it MUST include a
skipping to change at page 28, line 31 skipping to change at page 26, line 26
unknown. unknown.
If the above rules require R include a Path Vector TLV in the Label If the above rules require R include a Path Vector TLV in the Label
Mapping message, R computes it as follows: Mapping message, R computes it as follows:
o If the received Label Mapping message included a Path Vector, o If the received Label Mapping message included a Path Vector,
the Path Vector sent upstream MUST be the result of adding R's the Path Vector sent upstream MUST be the result of adding R's
LSR Id to the received Path Vector. LSR Id to the received Path Vector.
o If the received message had no Path Vector, the Path Vector o If the received message had no Path Vector, the Path Vector
sent upstream MUST be a path vector of length 1 containing R's sent upstream MUST be a Path Vector of length 1 containing R's
LSR Id. LSR Id.
- If the Label Mapping message is not being sent to propagate a - If the Label Mapping message is not being sent to propagate a
received message upstream, the Label Mapping message MUST received message upstream, the Label Mapping message MUST include
include a Path Vector of length 1 containing R's LSR Id. a Path Vector of length 1 containing R's LSR Id.
If R receives a Label Mapping message from its next hop with a If R receives a Label Mapping message from its next hop with a Hop
Hop Count TLV which exceeds the configured maximum value, or with Count TLV that exceeds the configured maximum value, or with a
a Path Vector TLV containing its own LSR Id or which exceeds the Path Vector TLV containing its own LSR Id or that exceeds the
maximum allowable length, then R detects that the corresponding maximum allowable length, then R detects that the corresponding
LSP contains a loop. LSP contains a loop.
When R detects a loop, it MUST stop using the label for forward- When R detects a loop, it MUST stop using the label for
ing, drop the Label Mapping message, and signal Loop Detected forwarding, drop the Label Mapping message, and signal Loop
status to the source of the Label Mapping message. Detected status to the source of the Label Mapping message.
2.8.3. Discussion 2.8.3. Discussion
If loop detection is desired in an MPLS domain, then it should be If Loop Detection is desired in an MPLS domain, then it should be
turned on in ALL LSRs within that MPLS domain, else loop detection turned on in ALL LSRs within that MPLS domain, else Loop Detection
will not operate properly and may result in undetected loops or in will not operate properly and may result in undetected loops or in
falsely detected loops. falsely detected loops.
LSRs which are configured for loop detection are NOT expected to LSRs that are configured for Loop Detection are NOT expected to store
store the path vectors as part of the LSP state. the Path Vectors as part of the LSP state.
Note that in a network where only non-merge capable LSRs are present, Note that in a network where only non-merge capable LSRs are present,
Path Vectors are passed downstream from ingress to egress, and are Path Vectors are passed downstream from ingress to egress, and are
not passed upstream. Even when merge is supported, Path Vectors need not passed upstream. Even when merge is supported, Path Vectors need
not be passed upstream along an LSP which is known to reach the not be passed upstream along an LSP that is known to reach the
egress. When an LSR experiences a change of next hop, it need pass egress. When an LSR experiences a change of next hop, it need pass
Path Vectors upstream only when it cannot tell from the hop count Path Vectors upstream only when it cannot tell from the hop count
that the change of next hop does not result in a loop. that the change of next hop does not result in a loop.
In the case of ordered label distribution, Label Mapping messages are In the case of ordered label distribution, Label Mapping messages are
propagated from egress toward ingress, naturally creating the Path propagated from egress toward ingress, naturally creating the Path
Vector along the way. In the case of independent label distribution, Vector along the way. In the case of independent label distribution,
an LSR may originate a Label Mapping message for an FEC before an LSR may originate a Label Mapping message for a FEC before
receiving a Label Mapping message from its downstream peer for that receiving a Label Mapping message from its downstream peer for that
FEC. In this case, the subsequent Label Mapping message for the FEC FEC. In this case, the subsequent Label Mapping message for the FEC
received from the downstream peer is treated as an update to LSP received from the downstream peer is treated as an update to LSP
attributes, and the Label Mapping message must be propagated attributes, and the Label Mapping message must be propagated
upstream. Thus, it is recommended that loop detection be configured upstream. Thus, it is recommended that Loop Detection be configured
in conjunction with ordered label distribution, to minimize the num- in conjunction with ordered label distribution, to minimize the
ber of Label Mapping update messages. number of Label Mapping update messages.
2.9. Authenticity and Integrity of LDP Messages 2.9. Authenticity and Integrity of LDP Messages
This section specifies a mechanism to protect against the introduc- This section specifies a mechanism to protect against the
tion of spoofed TCP segments into LDP session connection streams. introduction of spoofed TCP segments into LDP session connection
The use of this mechanism MUST be supported as a configurable option. streams. The use of this mechanism MUST be supported as a
configurable option.
The mechanism is based on use of the TCP MD5 Signature Option speci- The mechanism is based on use of the TCP MD5 Signature Option
fied in [RFC2385] for use by BGP [RFC4271]. See [RFC1321] for a specified in [RFC2385] for use by BGP [RFC4271]. See [RFC1321] for a
specification of the MD5 hash function. From a standards maturity specification of the MD5 hash function. From a standards maturity
point of view, the current document relates to [RFC2385] the same way point of view, the current document relates to [RFC2385] the same way
as [RFC4271] relates to [RFC2385]. This is explained in [RFC4278]. as [RFC4271] relates to [RFC2385]. This is explained in [RFC4278].
2.9.1. TCP MD5 Signature Option 2.9.1. TCP MD5 Signature Option
The following quotes from [RFC2385] outline the security properties The following quotes from [RFC2385] outline the security properties
achieved by using the TCP MD5 Signature Option and summarizes its achieved by using the TCP MD5 Signature Option and summarize its
operation: operation:
"IESG Note "IESG Note
This document describes current existing practice for securing This document describes current existing practice for securing
BGP against certain simple attacks. It is understood to have BGP against certain simple attacks. It is understood to have
security weaknesses against concerted attacks." security weaknesses against concerted attacks."
"Abstract "Abstract
This memo describes a TCP extension to enhance security for This memo describes a TCP extension to enhance security for
BGP. It defines a new TCP option for carrying an MD5 [RFC1321] BGP. It defines a new TCP option for carrying an MD5 [RFC1321]
digest in a TCP segment. This digest acts like a signature for digest in a TCP segment. This digest acts like a signature for
that segment, incorporating information known only to the con- that segment, incorporating information known only to the
nection end points. Since BGP uses TCP as its transport, using connection end points. Since BGP uses TCP as its transport,
this option in the way described in this paper significantly using this option in the way described in this paper
reduces the danger from certain security attacks on BGP." significantly reduces the danger from certain security attacks
on BGP."
"Introduction "Introduction
The primary motivation for this option is to allow BGP to pro- The primary motivation for this option is to allow BGP to
tect itself against the introduction of spoofed TCP segments protect itself against the introduction of spoofed TCP segments
into the connection stream. Of particular concern are TCP into the connection stream. Of particular concern are TCP
resets. resets.
To spoof a connection using the scheme described in this paper, To spoof a connection using the scheme described in this paper,
an attacker would not only have to guess TCP sequence numbers, an attacker would not only have to guess TCP sequence numbers,
but would also have had to obtain the password included in the but would also have had to obtain the password included in the
MD5 digest. This password never appears in the connection MD5 digest. This password never appears in the connection
stream, and the actual form of the password is up to the appli- stream, and the actual form of the password is up to the
cation. It could even change during the lifetime of a particu- application. It could even change during the lifetime of a
lar connection so long as this change was synchronized on both particular connection so long as this change was synchronized
ends (although retransmission can become problematical in some on both ends (although retransmission can become problematical
TCP implementations with changing passwords). in some TCP implementations with changing passwords).
Finally, there is no negotiation for the use of this option in Finally, there is no negotiation for the use of this option in
a connection, rather it is purely a matter of site policy a connection, rather it is purely a matter of site policy
whether or not its connections use the option." whether or not its connections use the option."
"MD5 as a Hashing Algorithm "MD5 as a Hashing Algorithm
Since this memo was first issued (under a different title), the Since this memo was first issued (under a different title), the
MD5 algorithm has been found to be vulnerable to collision MD5 algorithm has been found to be vulnerable to collision
search attacks [Dobb], and is considered by some to be search attacks [Dobb], and is considered by some to be
skipping to change at page 31, line 30 skipping to change at page 29, line 19
which contains an algorithm type field. which contains an algorithm type field.
This would need to be addressed in another document, however." This would need to be addressed in another document, however."
End of quotes from [RFC2385]. End of quotes from [RFC2385].
2.9.2. LDP Use of TCP MD5 Signature Option 2.9.2. LDP Use of TCP MD5 Signature Option
LDP uses the TCP MD5 Signature Option as follows: LDP uses the TCP MD5 Signature Option as follows:
- Use of the MD5 Signature Option for LDP TCP connections is a con- - Use of the MD5 Signature Option for LDP TCP connections is a
figurable LSR option. configurable LSR option.
- An LSR that uses the MD5 Signature Option is configured with a - An LSR that uses the MD5 Signature Option is configured with a
password (shared secret) for each potential LDP peer. password (shared secret) for each potential LDP peer.
- The LSR applies the MD5 algorithm as specified in [RFC2385] to - The LSR applies the MD5 algorithm as specified in [RFC2385] to
compute the MD5 digest for a TCP segment to be sent to a peer. compute the MD5 digest for a TCP segment to be sent to a peer.
This computation makes use of the peer password as well as the This computation makes use of the peer password as well as the
TCP segment. TCP segment.
- When the LSR receives a TCP segment with an MD5 digest, it vali- - When the LSR receives a TCP segment with an MD5 digest, it
dates the segment by calculating the MD5 digest (using its own validates the segment by calculating the MD5 digest (using its
record of the password) and compares the computed digest with the own record of the password) and compares the computed digest
received digest. If the comparison fails, the segment is dropped with the received digest. If the comparison fails, the segment
without any response to the sender. is dropped without any response to the sender.
- The LSR ignores LDP Hellos from any LSR for which a password has - The LSR ignores LDP Hellos from any LSR for which a password
not been configured. This ensures that the LSR establishes LDP has not been configured. This ensures that the LSR establishes
TCP connections only with LSRs for which a password has been con- LDP TCP connections only with LSRs for which a password has
figured. been configured.
2.10. Label Distribution for Explicitly Routed LSPs 2.10. Label Distribution for Explicitly Routed LSPs
Traffic Engineering [RFC2702] is expected to be an important MPLS Traffic Engineering [RFC2702] is expected to be an important MPLS
application. MPLS support for Traffic Engineering uses explicitly application. MPLS support for Traffic Engineering uses explicitly
routed LSPs, which need not follow normally-routed (hop-by-hop) paths routed LSPs, which need not follow normally-routed (hop-by-hop) paths
as determined by destination-based routing protocols. CR-LDP [CRLDP] as determined by destination-based routing protocols. CR-LDP [CRLDP]
defines extensions to LDP to use LDP to set up explicitly routed defines extensions to LDP to use LDP to set up explicitly routed
LSPs. LSPs.
3. Protocol Specification 3. Protocol Specification
Previous sections that describe LDP operation have discussed scenar- Previous sections that describe LDP operation have discussed
ios that involve the exchange of messages among LDP peers. This sec- scenarios that involve the exchange of messages among LDP peers.
tion specifies the message encodings and procedures for processing This section specifies the message encodings and procedures for
the messages. processing the messages.
LDP message exchanges are accomplished by sending LDP protocol data LDP message exchanges are accomplished by sending LDP protocol data
units (PDUs) over LDP session TCP connections. units (PDUs) over LDP session TCP connections.
Each LDP PDU can carry one or more LDP messages. Note that the mes- Each LDP PDU can carry one or more LDP messages. Note that the
sages in an LDP PDU need not be related to one another. For example, messages in an LDP PDU need not be related to one another. For
a single PDU could carry a message advertising FEC-label bindings for example, a single PDU could carry a message advertising FEC-label
several FECs, another message requesting label bindings for several bindings for several FECs, another message requesting label bindings
other FECs, and a third notification message signaling some event. for several other FECs, and a third Notification message signaling
some event.
3.1. LDP PDUs 3.1. LDP PDUs
Each LDP PDU is an LDP header followed by one or more LDP messages. Each LDP PDU is an LDP header followed by one or more LDP messages.
The LDP header is: The LDP header is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | PDU Length | | Version | PDU Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LDP Identifier | | LDP Identifier |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version Version
Two octet unsigned integer containing the version number of the proto- Two octet unsigned integer containing the version number of the
col. This version of the specification specifies LDP protocol version protocol. This version of the specification specifies LDP
1. protocol version 1.
PDU Length PDU Length
Two octet integer specifying the total length of this PDU in octets, Two octet integer specifying the total length of this PDU in
excluding the Version and PDU Length fields. octets, excluding the Version and PDU Length fields.
The maximum allowable PDU Length is negotiable when an LDP session is The maximum allowable PDU Length is negotiable when an LDP session
initialized. Prior to completion of the negotiation the maximum is initialized. Prior to completion of the negotiation, the
allowable length is 4096 bytes. maximum allowable length is 4096 bytes.
LDP Identifier LDP Identifier
Six octet field that uniquely identifies the label space of the send- Six octet field that uniquely identifies the label space of the
ing LSR for which this PDU applies. The first four octets identify sending LSR for which this PDU applies. The first four octets
the LSR and MUST be a globally unique value. It SHOULD be a 32-bit identify the LSR and MUST be a globally unique value. It SHOULD
router Id assigned to the LSR and also used to identify it in loop be a 32-bit router Id assigned to the LSR and also used to
detection Path Vectors. The last two octets identify a label space identify it in Loop Detection Path Vectors. The last two octets
within the LSR. For a platform-wide label space, these SHOULD both be identify a label space within the LSR. For a platform-wide label
zero. space, these SHOULD both be zero.
Note that there is no alignment requirement for the first octet of an Note that there is no alignment requirement for the first octet of an
LDP PDU. LDP PDU.
3.2. LDP Procedures 3.2. LDP Procedures
LDP defines messages, TLVs and procedures in the following areas: LDP defines messages, TLVs, and procedures in the following areas:
- Peer discovery; - Peer discovery
- Session management; - Session management
- Label distribution; - Label distribution
- Notification of errors and advisory information. - Notification of errors and advisory information
The sections that follow describe the message and TLV encodings for The sections that follow describe the message and TLV encodings for
these areas and the procedures that apply to them. these areas and the procedures that apply to them.
The label distribution procedures are complex and are difficult to The label distribution procedures are complex and are difficult to
describe fully, coherently and unambiguously as a collection of sepa- describe fully, coherently, and unambiguously as a collection of
rate message and TLV specifications. separate message and TLV specifications.
Appendix A, "LDP Label Distribution Procedures", describes the label Appendix A, "LDP Label Distribution Procedures", describes the label
distribution procedures in terms of label distribution events that distribution procedures in terms of label distribution events that
may occur at an LSR and how the LSR must respond. Appendix A is the may occur at an LSR and how the LSR must respond. Appendix A is the
specification of LDP label distribution procedures. If a procedure specification of LDP label distribution procedures. If a procedure
described elsewhere in this document conflicts with Appendix A, described elsewhere in this document conflicts with Appendix A,
Appendix A specifies LDP behavior. Appendix A specifies LDP behavior.
3.3. Type-Length-Value Encoding 3.3. Type-Length-Value Encoding
LDP uses a Type-Length-Value (TLV) encoding scheme to encode much of LDP uses a Type-Length-Value (TLV) encoding scheme to encode much of
the information carried in LDP messages. the information carried in LDP messages.
An LDP TLV is encoded as a 2 octet field that uses 14 bits to specify An LDP TLV is encoded as a 2 octet field that uses 14 bits to specify
a Type and 2 bits to specify behavior when an LSR doesn't recognize a Type and 2 bits to specify behavior when an LSR doesn't recognize
the Type, followed by a 2 octet Length Field, followed by a variable the Type, followed by a 2 octet Length field, followed by a variable
length Value field. length Value field.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type | Length | |U|F| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Value | | Value |
~ ~ ~ ~
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit U-bit
Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear
(=0), a notification MUST be returned to the message originator (=0), a notification MUST be returned to the message originator
and the entire message MUST be ignored; if U is set (=1), the and the entire message MUST be ignored; if U is set (=1), the
unknown TLV MUST be silently ignored and the rest of the message unknown TLV MUST be silently ignored and the rest of the message
processed as if the unknown TLV did not exist. The sections fol- processed as if the unknown TLV did not exist. The sections
lowing that define TLVs specify a value for the U-bit. following that define TLVs specify a value for the U-bit.
F bit F-bit
Forward unknown TLV bit. This bit applies only when the U bit is Forward unknown TLV bit. This bit applies only when the U-bit is
set and the LDP message containing the unknown TLV is to be for- set and the LDP message containing the unknown TLV is to be
warded. If F is clear (=0), the unknown TLV is not forwarded with forwarded. If F is clear (=0), the unknown TLV is not forwarded
the containing message; if F is set (=1), the unknown TLV is for- with the containing message; if F is set (=1), the unknown TLV is
warded with the containing message. The sections following that forwarded with the containing message. The sections following
define TLVs specify a value for the F-bit. By setting both the U that define TLVs specify a value for the F-bit. By setting both
and F bits, a TLV can be propagated as opaque data through nodes the U- and F-bits, a TLV can be propagated as opaque data through
that do not recognize the TLV. nodes that do not recognize the TLV.
Type Type
Encodes how the Value field is to be interpreted. Encodes how the Value field is to be interpreted.
Length Length
Specifies the length of the Value field in octets. Specifies the length of the Value field in octets.
Value Value
Octet string of Length octets that encodes information to be Octet string of Length octets that encodes information to be
interpreted as specified by the Type field. interpreted as specified by the Type field.
Note that there is no alignment requirement for the first octet of a Note that there is no alignment requirement for the first octet of a
TLV. TLV.
Note that the Value field itself may contain TLV encodings. That is, Note that the Value field itself may contain TLV encodings. That is,
TLVs may be nested. TLVs may be nested.
The TLV encoding scheme is very general. In principle, everything The TLV encoding scheme is very general. In principle, everything
appearing in an LDP PDU could be encoded as a TLV. This specifica- appearing in an LDP PDU could be encoded as a TLV. This
tion does not use the TLV scheme to its full generality. It is not specification does not use the TLV scheme to its full generality. It
used where its generality is unnecessary and its use would waste is not used where its generality is unnecessary and its use would
space unnecessarily. These are usually places where the type of a waste space unnecessarily. These are usually places where the type
value to be encoded is known, for example by its position in a mes- of a value to be encoded is known, for example by its position in a
sage or an enclosing TLV, and the length of the value is fixed or message or an enclosing TLV, and the length of the value is fixed or
readily derivable from the value encoding itself. readily derivable from the value encoding itself.
Some of the TLVs defined for LDP are similar to one another. For Some of the TLVs defined for LDP are similar to one another. For
example, there is a Generic Label TLV, an ATM Label TLV, and a Frame example, there is a Generic Label TLV, an ATM Label TLV, and a Frame
Relay TLV; see Sections "Generic Label TLV", "ATM Label TLV", and Relay TLV; see Sections "Generic Label TLV", "ATM Label TLV", and
"Frame Relay TLV". "Frame Relay TLV".
While it is possible to think about TLVs related in this way in terms While it is possible to think about TLVs related in this way in terms
of a TLV type that specifies a TLV class and a TLV subtype that spec- of a TLV type that specifies a TLV class and a TLV subtype that
ifies a particular kind of TLV within that class, this specification specifies a particular kind of TLV within that class, this
does not formalize the notion of a TLV subtype. specification does not formalize the notion of a TLV subtype.
The specification assigns type values for related TLVs, such as the The specification assigns type values for related TLVs, such as the
label TLVs, from a contiguous block in the 16-bit TLV type number label TLVs, from a contiguous block in the 16-bit TLV type number
space. space.
Section "TLV Summary" lists the TLVs defined in this version of the Section "TLV Summary" lists the TLVs defined in this version of the
protocol and the section in this document that describes each. protocol and the section in this document that describes each.
3.4. TLV Encodings for Commonly Used Parameters 3.4. TLV Encodings for Commonly Used Parameters
skipping to change at page 37, line 4 skipping to change at page 34, line 48
Prefix 0x02 See below. Prefix 0x02 See below.
Note that this version of LDP supports the use of multiple FEC Note that this version of LDP supports the use of multiple FEC
Elements per FEC for the Label Mapping message only. The use of Elements per FEC for the Label Mapping message only. The use of
multiple FEC Elements in other messages is not permitted in this multiple FEC Elements in other messages is not permitted in this
version, and is a subject for future study. version, and is a subject for future study.
Wildcard FEC Element Wildcard FEC Element
To be used only in the Label Withdraw and Label Release To be used only in the Label Withdraw and Label Release
Messages. Indicates the withdraw/release is to be applied to messages. Indicates the withdraw/release is to be applied to
all FECs associated with the label within the following label all FECs associated with the label within the following label
TLV. Must be the only FEC Element in the FEC TLV. TLV. Must be the only FEC Element in the FEC TLV.
Prefix FEC Element value encoding: Prefix FEC Element value encoding:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (2) | Address Family | PreLen | | Prefix (2) | Address Family | PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix | | Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Family Address Family
Two octet quantity containing a value from ADDRESS FAMILY NUM- Two octet quantity containing a value from ADDRESS FAMILY
BERS in [ASSIGNED_AF] that encodes the address family for the NUMBERS in [ASSIGNED_AF] that encodes the address family for
address prefix in the Prefix field. the address prefix in the Prefix field.
PreLen PreLen
One octet unsigned integer containing the length in bits of the One octet unsigned integer containing the length in bits of
address prefix that follows. A length of zero indicates a pre- the address prefix that follows. A length of zero indicates
fix that matches all addresses (the default destination); in a prefix that matches all addresses (the default
this case the Prefix itself is zero octets). destination); in this case, the Prefix itself is zero
octets).
Prefix Prefix
An address prefix encoded according to the Address Family An address prefix encoded according to the Address Family
field, whose length, in bits, was specified in the PreLen field, whose length, in bits, was specified in the PreLen
field, padded to a byte boundary. field, padded to a byte boundary.
3.4.1.1. FEC Procedures 3.4.1.1. FEC Procedures
If in decoding a FEC TLV an LSR encounters a FEC Element with an If in decoding a FEC TLV an LSR encounters a FEC Element with an
Address Family it does not support, it SHOULD stop decoding the FEC Address Family it does not support, it SHOULD stop decoding the FEC
skipping to change at page 38, line 8 skipping to change at page 35, line 48
signaling an error. signaling an error.
If it encounters a FEC Element type it cannot decode, it SHOULD stop If it encounters a FEC Element type it cannot decode, it SHOULD stop
decoding the FEC TLV, abort processing the message containing the decoding the FEC TLV, abort processing the message containing the
TLV, and send an "Unknown FEC" Notification message to its LDP peer TLV, and send an "Unknown FEC" Notification message to its LDP peer
signaling an error. signaling an error.
3.4.2. Label TLVs 3.4.2. Label TLVs
Label TLVs encode labels. Label TLVs are carried by the messages Label TLVs encode labels. Label TLVs are carried by the messages
used to advertise, request, release and withdraw label mappings. used to advertise, request, release, and withdraw label mappings.
There are several different kinds of Label TLVs which can appear in There are several different kinds of Label TLVs that can appear in
situations that require a Label TLV. situations that require a Label TLV.
3.4.2.1. Generic Label TLV 3.4.2.1. Generic Label TLV
An LSR uses Generic Label TLVs to encode labels for use on links for An LSR uses Generic Label TLVs to encode labels for use on links for
which label values are independent of the underlying link technology. which label values are independent of the underlying link technology.
Examples of such links are PPP and Ethernet. Examples of such links are PPP and Ethernet.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 39, line 4 skipping to change at page 36, line 42
An LSR uses ATM Label TLVs to encode labels for use on ATM links. An LSR uses ATM Label TLVs to encode labels for use on ATM links.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| ATM Label (0x0201) | Length | |0|0| ATM Label (0x0201) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Res| V | VPI | VCI | |Res| V | VPI | VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Res Res
This field is reserved. It MUST be set to zero on transmission This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt. and MUST be ignored on receipt.
V-bits V-bits
Two-bit switching indicator. If V-bits is 00, both the VPI and Two-bit switching indicator. If V-bits is 00, both the VPI and
VCI are significant. If V-bits is 01, only the VPI field is sig- VCI are significant. If V-bits is 01, only the VPI field is
nificant. If V-bit is 10, only the VCI is significant. significant. If V-bit is 10, only the VCI is significant.
VPI VPI
Virtual Path Identifier. If VPI is less than 12-bits it SHOULD be Virtual Path Identifier. If VPI is less than 12-bits it SHOULD be
right justified in this field and preceding bits SHOULD be set to right justified in this field and preceding bits SHOULD be set to
0. 0.
VCI VCI
Virtual Channel Identifier. If the VCI is less than 16- bits, it Virtual Channel Identifier. If the VCI is less than 16- bits, it
SHOULD be right justified in the field and the preceding bits MUST SHOULD be right justified in the field and the preceding bits MUST
be set to 0. If Virtual Path switching is indicated in the V-bits be set to 0. If Virtual Path switching is indicated in the V-bits
skipping to change at page 39, line 43 skipping to change at page 37, line 35
|0|0| Frame Relay Label (0x0202)| Length | |0|0| Frame Relay Label (0x0202)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Len| DLCI | | Reserved |Len| DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Res Res
This field is reserved. It MUST be set to zero on transmission This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt. and MUST be ignored on receipt.
Len Len
This field specifies the number of bits of the DLCI. The follow- This field specifies the number of bits of the DLCI. The
ing values are supported: following values are supported:
0 = 10 bits DLCI 0 = 10 bits of DLCI
2 = 23 bits DLCI 2 = 23 bits of DLCI
Len values 1 and 3 are reserved. Len values 1 and 3 are reserved.
DLCI DLCI
The Data Link Connection Identifier The Data Link Connection Identifier
For a 10-bit DLCI, the encoding is:
For a 10bit DLCI, the encoding is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Frame Relay Label (0x0202)| Length | |0|0| Frame Relay Label (0x0202)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Len| 0 | 10 bit DLCI | | Reserved |Len| 0 | 10-bit DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For a 23bit DLCI, the encoding is: For a 23-bit DLCI, the encoding is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Frame Relay Label (0x0202)| Length | |0|0| Frame Relay Label (0x0202)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Len| 23 bit DLCI | | Reserved |Len| 23-bit DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For further information, see [RFC3034]. For further information, see [RFC3034].
3.4.3. Address List TLV 3.4.3. Address List TLV
The Address List TLV appears in Address and Address Withdraw mes- The Address List TLV appears in Address and Address Withdraw
sages. messages.
Its encoding is: Its encoding is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Address List (0x0101) | Length | |0|0| Address List (0x0101) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family | | | Address Family | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
skipping to change at page 41, line 44 skipping to change at page 39, line 40
|0|0| Hop Count (0x0103) | Length | |0|0| Hop Count (0x0103) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HC Value | | HC Value |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
HC Value HC Value
1 octet unsigned integer hop count value. 1 octet unsigned integer hop count value.
3.4.4.1. Hop Count Procedures 3.4.4.1. Hop Count Procedures
During setup of an LSP an LSR R may receive a Label Mapping or Label During setup of an LSP, an LSR R may receive a Label Mapping or Label
Request message for the LSP that contains the Hop Count TLV. If it Request message for the LSP that contains the Hop Count TLV. If it
does, it SHOULD record the hop count value. does, it SHOULD record the hop count value.
If LSR R then propagates the Label Mapping message for the LSP to an If LSR R then propagates the Label Mapping message for the LSP to an
upstream peer or the Label Request message to a downstream peer to upstream peer or the Label Request message to a downstream peer to
continue the LSP setup, it must determine a hop count to include in continue the LSP setup, it must determine a hop count to include in
the propagated message as follows: the propagated message as follows:
- If the message is a Label Request message, R MUST increment the - If the message is a Label Request message, R MUST increment the
received hop count; received hop count;
skipping to change at page 42, line 23 skipping to change at page 40, line 18
o If R is a member of the edge set of an LSR domain whose LSRs do o If R is a member of the edge set of an LSR domain whose LSRs do
not perform 'TTL-decrement' and the upstream peer is within not perform 'TTL-decrement' and the upstream peer is within
that domain, R MUST reset the hop count to 1 before propagating that domain, R MUST reset the hop count to 1 before propagating
the message. the message.
o Otherwise, R MUST increment the received hop count. o Otherwise, R MUST increment the received hop count.
The first LSR in the LSP (ingress for a Label Request message, egress The first LSR in the LSP (ingress for a Label Request message, egress
for a Label Mapping message) SHOULD set the hop count value to 1. for a Label Mapping message) SHOULD set the hop count value to 1.
By convention a value of 0 indicates an unknown hop count. The By convention, a value of 0 indicates an unknown hop count. The
result of incrementing an unknown hop count is itself an unknown hop result of incrementing an unknown hop count is itself an unknown hop
count (0). count (0).
Use of the unknown hop count value greatly reduces the signaling Use of the unknown hop count value greatly reduces the signaling
overhead when independent control is used. When a new LSP is estab- overhead when independent control is used. When a new LSP is
lished, each LSR starts with unknown hop count. Addition of a new established, each LSR starts with an unknown hop count. Addition of
LSR whose hop count is also unknown does not cause a hop count update a new LSR whose hop count is also unknown does not cause a hop count
to be propagated upstream since the hop count remains unknown. When update to be propagated upstream since the hop count remains unknown.
the egress is finally added to the LSP, then the LSRs propagate hop When the egress is finally added to the LSP, then the LSRs propagate
count updates upstream via Label Mapping messages. hop count updates upstream via Label Mapping messages.
Without use of the unknown hop count, each time a new LSR is added to Without use of the unknown hop count, each time a new LSR is added to
the LSP a hop count update would need to be propagated upstream if the LSP a hop count update would need to be propagated upstream if
the new LSR is closer to the egress than any of the other LSRs. the new LSR is closer to the egress than any of the other LSRs.
These updates are useless overhead since they don't reflect the hop These updates are useless overhead since they don't reflect the hop
count to the egress. count to the egress.
>From the perspective of the ingress node, the fact that the hop From the perspective of the ingress node, the fact that the hop count
count is unknown implies nothing about whether a packet sent on the is unknown implies nothing about whether a packet sent on the LSP
LSP will actually make it to the egress. All it implies is that the will actually make it to the egress. All it implies is that the hop
hop count update from the egress has not yet reached the ingress. count update from the egress has not yet reached the ingress.
If an LSR receives a message containing a Hop Count TLV, it MUST If an LSR receives a message containing a Hop Count TLV, it MUST
check the hop count value to determine whether the hop count has check the hop count value to determine whether the hop count has
exceeded its configured maximum allowable value. If so, it MUST exceeded its configured maximum allowable value. If so, it MUST
behave as if the containing message has traversed a loop by sending a behave as if the containing message has traversed a loop by sending a
Notification message signaling Loop Detected in reply to the sender Notification message signaling Loop Detected in reply to the sender
of the message. of the message.
If Loop Detection is configured, the LSR MUST follow the procedures If Loop Detection is configured, the LSR MUST follow the procedures
specified in Section "Loop Detection". specified in Section "Loop Detection".
3.4.5. Path Vector TLV 3.4.5. Path Vector TLV
The Path Vector TLV is used with the Hop Count TLV in Label Request The Path Vector TLV is used with the Hop Count TLV in Label Request
and Label Mapping messages to implement the optional LDP loop detec- and Label Mapping messages to implement the optional LDP Loop
tion mechanism. See Section "Loop Detection". Its use in the Label Detection mechanism. See Section "Loop Detection". Its use in the
Request message records the path of LSRs the request has traversed. Label Request message records the path of LSRs the request has
Its use in the Label Mapping message records the path of LSRs a label traversed. Its use in the Label Mapping message records the path of
advertisement has traversed to setup an LSP. Its encoding is: LSRs a label advertisement has traversed to set up an LSP. Its
encoding is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Path Vector (0x0104) | Length | |0|0| Path Vector (0x0104) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSR Id 1 | | LSR Id 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
skipping to change at page 43, line 32 skipping to change at page 41, line 30
| LSR Id 1 | | LSR Id 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSR Id n | | LSR Id n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
One or more LSR Ids One or more LSR Ids
A list of router-ids indicating the path of LSRs the message has A list of router-ids indicating the path of LSRs the message has
traversed. Each LSR Id is the first four octets (router-id) of traversed. Each LSR Id is the first four octets (router-id) of
the LDP identifier for the corresponding LSR. This ensures it is the LDP Identifier for the corresponding LSR. This ensures it is
unique within the LSR network. unique within the LSR network.
3.4.5.1. Path Vector Procedures 3.4.5.1. Path Vector Procedures
The Path Vector TLV is carried in Label Mapping and Label Request The Path Vector TLV is carried in Label Mapping and Label Request
messages when loop detection is configured. messages when Loop Detection is configured.
3.4.5.1.1. Label Request Path Vector 3.4.5.1.1. Label Request Path Vector
Section "Loop Detection" specifies situations when an LSR must Section "Loop Detection" specifies situations when an LSR must
include a Path Vector TLV in a Label Request message. include a Path Vector TLV in a Label Request message.
An LSR that receives a Path Vector in a Label Request message MUST An LSR that receives a Path Vector in a Label Request message MUST
perform the procedures described in Section "Loop Detection". perform the procedures described in Section "Loop Detection".
If the LSR detects a loop, it MUST reject the Label Request message. If the LSR detects a loop, it MUST reject the Label Request message.
The LSR MUST: The LSR MUST:
1. Transmit a Notification message to the sending LSR signaling 1. Transmit a Notification message to the sending LSR signaling
"Loop Detected". "Loop Detected".
2. Not propagate the Label Request message further. 2. Not propagate the Label Request message further.
Note that a Label Request message with Path Vector TLV is forwarded Note that a Label Request message with a Path Vector TLV is forwarded
until: until:
1. A loop is found, 1. A loop is found,
2. The LSP egress is reached, 2. The LSP egress is reached, or
3. The maximum Path Vector limit or maximum Hop Count limit is 3. The maximum Path Vector limit or maximum Hop Count limit is
reached. This is treated as if a loop had been detected. reached. This is treated as if a loop had been detected.
3.4.5.1.2. Label Mapping Path Vector 3.4.5.1.2. Label Mapping Path Vector
Section "Loop Detection" specifies the situations when an LSR must Section "Loop Detection" specifies the situations when an LSR must
include a Path Vector TLV in a Label Mapping message. include a Path Vector TLV in a Label Mapping message.
An LSR that receives a Path Vector in a Label Mapping message MUST An LSR that receives a Path Vector in a Label Mapping message MUST
skipping to change at page 44, line 41 skipping to change at page 42, line 39
If the LSR detects a loop, it MUST reject the Label Mapping message If the LSR detects a loop, it MUST reject the Label Mapping message
in order to prevent a forwarding loop. The LSR MUST: in order to prevent a forwarding loop. The LSR MUST:
1. Transmit a Label Release message carrying a Status TLV to the 1. Transmit a Label Release message carrying a Status TLV to the
sending LSR to signal "Loop Detected". sending LSR to signal "Loop Detected".
2. Not propagate the message further. 2. Not propagate the message further.
3. Check whether the Label Mapping message is for an existing LSP. 3. Check whether the Label Mapping message is for an existing LSP.
If so, the LSR must unsplice any upstream labels which are If so, the LSR must unsplice any upstream labels that are
spliced to the downstream label for the FEC. spliced to the downstream label for the FEC.
Note that a Label Mapping message with a Path Vector TLV is forwarded Note that a Label Mapping message with a Path Vector TLV is forwarded
until: until:
1. A loop is found, 1. A loop is found,
2. An LSP ingress is reached, or 2. An LSP ingress is reached, or
3. The maximum Path Vector or maximum Hop Count limit is reached. 3. The maximum Path Vector or maximum Hop Count limit is reached.
skipping to change at page 45, line 4 skipping to change at page 42, line 50
spliced to the downstream label for the FEC. spliced to the downstream label for the FEC.
Note that a Label Mapping message with a Path Vector TLV is forwarded Note that a Label Mapping message with a Path Vector TLV is forwarded
until: until:
1. A loop is found, 1. A loop is found,
2. An LSP ingress is reached, or 2. An LSP ingress is reached, or
3. The maximum Path Vector or maximum Hop Count limit is reached. 3. The maximum Path Vector or maximum Hop Count limit is reached.
This is treated as if a loop had been detected. This is treated as if a loop had been detected.
3.4.6. Status TLV 3.4.6. Status TLV
Notification messages carry Status TLVs to specify events being sig- Notification messages carry Status TLVs to specify events being
naled. signaled.
The encoding for the Status TLV is: The encoding for the Status TLV is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Status (0x0300) | Length | |U|F| Status (0x0300) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code | | Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit U-bit
SHOULD be 0 when the Status TLV is sent in a Notification message. SHOULD be 0 when the Status TLV is sent in a Notification message.
SHOULD be 1 when the Status TLV is sent in some other message. SHOULD be 1 when the Status TLV is sent in some other message.
F bit F-bit
SHOULD be the same as the setting of the F-bit in the Status Code SHOULD be the same as the setting of the F-bit in the Status Code
field. field.
Status Code Status Code
32-bit unsigned integer encoding the event being signaled. The 32-bit unsigned integer encoding the event being signaled. The
structure of a Status Code is: structure of a Status Code is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E|F| Status Data | |E|F| Status Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
E bit E-bit
Fatal error bit. If set (=1), this is a fatal error notifica- Fatal error bit. If set (=1), this is a fatal Error
tion. If clear (=0), this is an advisory notification. Notification. If clear (=0), this is an Advisory Notification.
F bit F-bit
Forward bit. If set (=1), the notification SHOULD be forwarded Forward bit. If set (=1), the notification SHOULD be forwarded
to the LSR for the next-hop or previous-hop for the LSP, if to the LSR for the next-hop or previous-hop for the LSP, if
any, associated with the event being signaled. If clear (=0), any, associated with the event being signaled. If clear (=0),
the notification SHOULD NOT be forwarded. the notification SHOULD NOT be forwarded.
Status Data Status Data
30-bit unsigned integer which specifies the status information. 30-bit unsigned integer that specifies the status information.
This specification defines Status Codes (32-bit unsigned integers This specification defines Status Codes (32-bit unsigned
with the above encoding). integers with the above encoding).
A Status Code of 0 signals success. A Status Code of 0 signals success.
Message ID Message ID
If non-zero, 32-bit value that identifies the peer message to If non-zero, 32-bit value that identifies the peer message to
which the Status TLV refers. If zero, no specific peer message is which the Status TLV refers. If zero, no specific peer message is
being identified. being identified.
Message Type Message Type
If non-zero, the type of the peer message to which the Status TLV If non-zero, the type of the peer message to which the Status TLV
refers. If zero, the Status TLV does not refer to any specific refers. If zero, the Status TLV does not refer to any specific
message type. message type.
Note that use of the Status TLV is not limited to Notification mes- Note that use of the Status TLV is not limited to Notification
sages. A message other than a Notification message may carry a Sta- messages. A message other than a Notification message may carry a
tus TLV as an Optional Parameter. When a message other than a Noti- Status TLV as an Optional Parameter. When a message other than a
fication carries a Status TLV the U-bit of the Status TLV SHOULD be Notification carries a Status TLV, the U-bit of the Status TLV SHOULD
set to 1 to indicate that the receiver SHOULD silently discard the be set to 1 to indicate that the receiver SHOULD silently discard the
TLV if unprepared to handle it. TLV if unprepared to handle it.
3.5. LDP Messages 3.5. LDP Messages
All LDP messages have the following format: All LDP messages have the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Message Type | Message Length | |U| Message Type | Message Length |
skipping to change at page 47, line 24 skipping to change at page 45, line 4
| Mandatory Parameters | | Mandatory Parameters |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| Optional Parameters | | Optional Parameters |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U-bit
U bit
Unknown message bit. Upon receipt of an unknown message, if U is Unknown message bit. Upon receipt of an unknown message, if U is
clear (=0), a notification is returned to the message originator; clear (=0), a notification is returned to the message originator;
if U is set (=1), the unknown message is silently ignored. The if U is set (=1), the unknown message is silently ignored. The
sections following that define messages specify a value for the U- sections following that define messages specify a value for the
bit. U-bit.
Message Type Message Type
Identifies the type of message Identifies the type of message.
Message Length Message Length
Specifies the cumulative length in octets of the Message ID, Specifies the cumulative length in octets of the Message ID,
Mandatory Parameters, and Optional Parameters. Mandatory Parameters, and Optional Parameters.
Message ID Message ID
32-bit value used to identify this message. Used by the sending 32-bit value used to identify this message. Used by the sending
LSR to facilitate identifying notification messages that may apply LSR to facilitate identifying Notification messages that may apply
to this message. An LSR sending a notification message in to this message. An LSR sending a Notification message in
response to this message SHOULD include this Message Id in the response to this message SHOULD include this Message ID in the
Status TLV carried by the notification message; see Section "Noti- Status TLV carried by the Notification message; see Section
fication Message". "Notification Message".
Mandatory Parameters Mandatory Parameters
Variable length set of required message parameters. Some messages Variable length set of required message parameters. Some messages
have no required parameters. have no required parameters.
For messages that have required parameters, the required parame- For messages that have required parameters, the required
ters MUST appear in the order specified by the individual message parameters MUST appear in the order specified by the individual
specifications in the sections that follow. message specifications in the sections that follow.
Optional Parameters Optional Parameters
Variable length set of optional message parameters. Many messages Variable length set of optional message parameters. Many messages
have no optional parameters. have no optional parameters.
For messages that have optional parameters, the optional parame- For messages that have optional parameters, the optional
ters may appear in any order. parameters may appear in any order.
Note that there is no alignment requirement for the first octet of an Note that there is no alignment requirement for the first octet of an
LDP message and that there is no padding at the end of a message; LDP message and that there is no padding at the end of a message;
that is, parameters can end at odd-byte boundaries. that is, parameters can end at odd-byte boundaries.
The following message types are defined in this version of LDP: The following message types are defined in this version of LDP:
Message Name Section Title Message Name Section Title
Notification "Notification Message" Notification "Notification Message"
skipping to change at page 48, line 47 skipping to change at page 46, line 35
the Label Mapping, Label Request, Label Withdraw, and Label Release the Label Mapping, Label Request, Label Withdraw, and Label Release
messages. messages.
While it is possible to think about messages related in this way in While it is possible to think about messages related in this way in
terms of a message type that specifies a message class and a message terms of a message type that specifies a message class and a message
subtype that specifies a particular kind of message within that subtype that specifies a particular kind of message within that
class, this specification does not formalize the notion of a message class, this specification does not formalize the notion of a message
subtype. subtype.
The specification assigns type values for related messages, such as The specification assigns type values for related messages, such as
the label messages, from of a contiguous block in the 16-bit message the Label messages, from of a contiguous block in the 16-bit message
type number space. type number space.
3.5.1. Notification Message 3.5.1. Notification Message
An LSR sends a Notification message to inform an LDP peer of a sig- An LSR sends a Notification message to inform an LDP peer of a
nificant event. A Notification message signals a fatal error or pro- significant event. A Notification message signals a fatal error or
vides advisory information such as the outcome of processing an LDP provides advisory information such as the outcome of processing an
message or the state of the LDP session. LDP message or the state of the LDP session.
The encoding for the Notification Message is: The encoding for the Notification message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Notification (0x0001) | Message Length | |0| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) | | Status (TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 49, line 36 skipping to change at page 47, line 29
Message ID Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
Status TLV Status TLV
Indicates the event being signaled. The encoding for the Status Indicates the event being signaled. The encoding for the Status
TLV is specified in Section "Status TLV". TLV is specified in Section "Status TLV".
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The following Optional Parameters are generic encoded as a TLV. The following Optional Parameters are generic
and may appear in any Notification Message: and may appear in any Notification message:
Optional Parameter Type Length Value Optional Parameter Type Length Value
Extended Status 0x0301 4 See below Extended Status 0x0301 4 See below
Returned PDU 0x0302 var See below Returned PDU 0x0302 var See below
Returned Message 0x0303 var See below Returned Message 0x0303 var See below
Other Optional Parameters, specific to the particular event being Other Optional Parameters, specific to the particular event being
signaled by the Notification Messages may appear. These are signaled by the Notification messages, may appear. These are
described elsewhere. described elsewhere.
Extended Status Extended Status
The 4 octet value is an Extended Status Code that encodes addi- The 4 octet value is an Extended Status Code that encodes
tional information that supplements the status information con- additional information that supplements the status information
tained in the Notification Status Code. contained in the Notification Status Code.
Returned PDU Returned PDU
An LSR uses this parameter to return part of an LDP PDU to the An LSR uses this parameter to return part of an LDP PDU to the LSR
LSR that sent it. The value of this TLV is the PDU header and that sent it. The value of this TLV is the PDU header and as much
as much PDU data following the header as appropriate for the PDU data following the header as appropriate for the condition
condition being signaled by the Notification message. being signaled by the Notification message.
Returned Message Returned Message
An LSR uses this parameter to return part of an LDP message to An LSR uses this parameter to return part of an LDP message to the
the LSR that sent it. The value of this TLV is the message LSR that sent it. The value of this TLV is the message type and
type and length fields and as much message data following the length fields and as much message data following the type and
type and length fields as appropriate for the condition being length fields as appropriate for the condition being signaled by
signaled by the Notification message. the Notification message.
3.5.1.1. Notification Message Procedures 3.5.1.1. Notification Message Procedures
If an LSR encounters a condition requiring it to notify its peer with If an LSR encounters a condition requiring it to notify its peer with
advisory or error information it sends the peer a Notification mes- advisory or error information, it sends the peer a Notification
sage containing a Status TLV that encodes the information and option- message containing a Status TLV that encodes the information and
ally additional TLVs that provide more information about the condi- optionally additional TLVs that provide more information about the
tion. condition.
If the condition is one that is a fatal error the Status Code carried If the condition is one that is a fatal error, the Status Code
in the notification will indicate that. In this case, after sending carried in the Notification will indicate that. In this case, after
the Notification message the LSR SHOULD terminate the LDP session by sending the Notification message the LSR SHOULD terminate the LDP
closing the session TCP connection and discard all state associated session by closing the session TCP connection and discard all state
with the session, including all label-FEC bindings learned via the associated with the session, including all label-FEC bindings learned
session. via the session.
When an LSR receives a Notification message that carries a Status When an LSR receives a Notification message that carries a Status
Code that indicates a fatal error, it SHOULD terminate the LDP ses- Code that indicates a fatal error, it SHOULD terminate the LDP
sion immediately by closing the session TCP connection and discard session immediately by closing the session TCP connection and discard
all state associated with the session, including all label-FEC bind- all state associated with the session, including all label-FEC
ings learned via the session. bindings learned via the session.
The above statement does not apply to the processing of the Shutdown The above statement does not apply to the processing of the Shutdown
message in the session initialization procedure. When an LSR receives message in the session initialization procedure. When an LSR
a Shutdown message during session initialization, it SHOULD transmit receives a Shutdown message during session initialization, it SHOULD
a Shutdown message and then close the transport connection. transmit a Shutdown message and then close the transport connection.
3.5.1.2. Events Signaled by Notification Messages 3.5.1.2. Events Signaled by Notification Messages
It is useful for descriptive purpose to classify events signaled by It is useful for descriptive purpose to classify events signaled by
Notification Messages into the following categories. Notification messages into the following categories.
3.5.1.2.1. Malformed PDU or Message 3.5.1.2.1. Malformed PDU or Message
Malformed LDP PDUs or Messages that are part of the LDP Discovery Malformed LDP PDUs or messages that are part of the LDP Discovery
mechanism are handled by silently discarding them. mechanism are handled by silently discarding them.
An LDP PDU received on a TCP connection for an LDP session is mal- An LDP PDU received on a TCP connection for an LDP session is
formed if: malformed if:
- The LDP Identifier in the PDU header is unknown to the - The LDP Identifier in the PDU header is unknown to the
receiver, or it is known but is not the LDP Identifier associ- receiver, or it is known but is not the LDP Identifier
ated by the receiver with the LDP peer for this LDP session. associated by the receiver with the LDP peer for this LDP
This is a fatal error signaled by the Bad LDP Identifier Status session. This is a fatal error signaled by the Bad LDP
Code. Identifier Status Code.
- The LDP protocol version is not supported by the receiver, or - The LDP protocol version is not supported by the receiver, d or
it is supported but is not the version negotiated for the ses- it is supported but is not the version negotiated for the
sion during session establishment. This is a fatal error sig- session during session establishment. This is a fatal error
naled by the Bad Protocol Version Status Code. signaled by the Bad Protocol Version Status Code.
- The PDU Length field is too small (< 14) or too large - The PDU Length field is too small (< 14) or too large (>
(> maximum PDU length). This is a fatal error signaled by the maximum PDU length). This is a fatal error signaled by the Bad
Bad PDU Length Status Code. Section "Initialization Message" PDU Length Status Code. Section "Initialization Message"
describes how the maximum PDU length for a session is deter- describes how the maximum PDU length for a session is
mined. determined.
An LDP Message is malformed if: An LDP message is malformed if:
- The Message Type is unknown. - The Message Type is unknown.
If the Message Type is < 0x8000 (high order bit = 0) it is an If the Message Type is < 0x8000 (high order bit = 0), it is an
error signaled by the Unknown Message Type Status Code. error signaled by the Unknown Message Type Status Code.
If the Message Type is >= 0x8000 (high order bit = 1) it is If the Message Type is >= 0x8000 (high order bit = 1), it is
silently discarded. silently discarded.
- The Message Length is too large, that is, indicates that the - The Message Length is too large, that is, indicates that the
message extends beyond the end of the containing LDP PDU. This message extends beyond the end of the containing LDP PDU. This
is a fatal error signaled by the Bad Message Length Status is a fatal error signaled by the Bad Message Length Status
Code. Code.
- The Message Length is too small, that is, smaller than the - The Message Length is too small, that is, smaller than the
smallest possible value component. This is a fatal error sig- smallest possible value component. This is a fatal error
naled by the Bad Message Length Status Code. signaled by the Bad Message Length Status Code.
- The message is missing one or more Mandatory Parameters. This - The message is missing one or more Mandatory Parameters. This
is a non-fatal error signaled by the Missing Message Parameters is a non-fatal error signaled by the Missing Message Parameters
Status Code. Status Code.
3.5.1.2.2. Unknown or Malformed TLV 3.5.1.2.2. Unknown or Malformed TLV
Malformed TLVs contained in LDP messages that are part of the LDP Malformed TLVs contained in LDP messages that are part of the LDP
Discovery mechanism are handled by silently discarding the containing Discovery mechanism are handled by silently discarding the containing
message. message.
A TLV contained in an LDP message received on a TCP connection of an A TLV contained in an LDP message received on a TCP connection of an
LDP is malformed if: LDP is malformed if:
- The TLV Length is too large, that is, indicates that the TLV - The TLV Length is too large, that is, indicates that the TLV
extends beyond the end of the containing message. This is a extends beyond the end of the containing message. This is a
fatal error signaled by the Bad TLV Length Status Code. fatal error signaled by the Bad TLV Length Status Code.
- The TLV type is unknown. - The TLV type is unknown.
If the TLV type is < 0x8000 (high order bit 0) it is an error If the TLV type is < 0x8000 (high order bit = 0), it is an
signaled by the Unknown TLV Status Code. error signaled by the Unknown TLV Status Code.
If the TLV type is >= 0x8000 (high order bit 1) the TLV is If the TLV type is >= 0x8000 (high order bit = 1), the TLV is
silently dropped. silently dropped.
- The TLV Value is malformed. This occurs when the receiver han- - The TLV Value is malformed. This occurs when the receiver
dles the TLV but cannot decode the TLV Value. This is inter- handles the TLV but cannot decode the TLV Value. This is
preted as indicative of a bug in either the sending or receiv- interpreted as indicative of a bug in either the sending or
ing LSR. It is a fatal error signaled by the Malformed TLV receiving LSR. It is a fatal error signaled by the Malformed
Value Status Code. TLV Value Status Code.
3.5.1.2.3. Session KeepAlive Timer Expiration 3.5.1.2.3. Session KeepAlive Timer Expiration
This is a fatal error signaled by the KeepAlive Timer Expired Status This is a fatal error signaled by the KeepAlive Timer Expired Status
Code. Code.
3.5.1.2.4. Unilateral Session Shutdown 3.5.1.2.4. Unilateral Session Shutdown
This is a fatal event signaled by the Shutdown Status Code. The This is a fatal event signaled by the Shutdown Status Code. The
Notification Message may optionally include an Extended Status TLV to Notification message may optionally include an Extended Status TLV to
provide a reason for the Shutdown. The sending LSR terminates the provide a reason for the Shutdown. The sending LSR terminates the
session immediately after sending the Notification. session immediately after sending the Notification.
3.5.1.2.5. Initialization Message Events 3.5.1.2.5. Initialization Message Events
The session initialization negotiation (see Section "Session Initial- The session initialization negotiation (see Section "Session
ization") may fail if the session parameters received in the Initial- Initialization") may fail if the session parameters received in the
ization Message are unacceptable. This is a fatal error. The spe- Initialization message are unacceptable. This is a fatal error. The
cific Status Code depends on the parameter deemed unacceptable, and specific Status Code depends on the parameter deemed unacceptable,
is defined in Sections "Initialization Message". and is defined in Sections "Initialization Message".
3.5.1.2.6. Events Resulting From Other Messages 3.5.1.2.6. Events Resulting from Other Messages
Messages other than the Initialization message may result in events Messages other than the Initialization message may result in events
that must be signaled to LDP peers via Notification Messages. These that must be signaled to LDP peers via Notification messages. These
events and the Status Codes used in the Notification Messages to sig- events and the Status Codes used in the Notification messages to
nal them are described in the sections that describe these messages. signal them are described in the sections that describe these
messages.
3.5.1.2.7. Internal Errors 3.5.1.2.7. Internal Errors
An LDP implementation may be capable of detecting problem conditions An LDP implementation may be capable of detecting problem conditions
specific to its implementation. When such a condition prevents an specific to its implementation. When such a condition prevents an
implementation from interacting correctly with a peer, the implemen- implementation from interacting correctly with a peer, the
tation should, when capable of doing so, use the Internal Error Sta- implementation should, when capable of doing so, use the Internal
tus Code to signal the peer. This is a fatal error. Error Status Code to signal the peer. This is a fatal error.
3.5.1.2.8. Miscellaneous Events 3.5.1.2.8. Miscellaneous Events
These are events that fall into none of the categories above. There These are events that fall into none of the categories above. There
are no miscellaneous events defined in this version of the protocol. are no miscellaneous events defined in this version of the protocol.
3.5.2. Hello Message 3.5.2. Hello Message
LDP Hello Messages are exchanged as part of the LDP Discovery Mecha- LDP Hello messages are exchanged as part of the LDP Discovery
nism; see Section "LDP Discovery". Mechanism; see Section "LDP Discovery".
The encoding for the Hello Message is: The encoding for the Hello message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Hello (0x0100) | Message Length | |0| Hello (0x0100) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Hello Parameters TLV | | Common Hello Parameters TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 54, line 16 skipping to change at page 52, line 4
Specifies parameters common to all Hello messages. The encoding Specifies parameters common to all Hello messages. The encoding
for the Common Hello Parameters TLV is: for the Common Hello Parameters TLV is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Common Hello Parms(0x0400)| Length | |0|0| Common Hello Parms(0x0400)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hold Time |T|R| Reserved | | Hold Time |T|R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Hold Time
Hold Time, Hello hold time in seconds. An LSR maintains a record of
Hello hold time in seconds. An LSR maintains a record of Hel- Hellos received from potential peers (see Section "Hello
los received from potential peers (see Section "Hello Message Message Procedures"). Hello Hold Time specifies the time the
Procedures"). Hello Hold Time specifies the time the sending sending LSR will maintain its record of Hellos from the
LSR will maintain its record of Hellos from the receiving LSR receiving LSR without receipt of another Hello.
without receipt of another Hello.
A pair of LSRs negotiates the hold times they use for Hellos A pair of LSRs negotiates the hold times they use for Hellos
from each other. Each proposes a hold time. The hold time from each other. Each proposes a hold time. The hold time
used is the minimum of the hold times proposed in their Hellos. used is the minimum of the hold times proposed in their Hellos.
A value of 0 means use the default, which is 15 seconds for A value of 0 means use the default, which is 15 seconds for
Link Hellos and 45 seconds for Targeted Hellos. A value of Link Hellos and 45 seconds for Targeted Hellos. A value of
0xffff means infinite. 0xffff means infinite.
T, Targeted Hello T, Targeted Hello
skipping to change at page 54, line 44 skipping to change at page 52, line 31
value of 0 specifies that this Hello is a Link Hello. value of 0 specifies that this Hello is a Link Hello.
R, Request Send Targeted Hellos R, Request Send Targeted Hellos
A value of 1 requests the receiver to send periodic Targeted A value of 1 requests the receiver to send periodic Targeted
Hellos to the source of this Hello. A value of 0 makes no Hellos to the source of this Hello. A value of 0 makes no
request. request.
An LSR initiating Extended Discovery sets R to 1. If R is 1, An LSR initiating Extended Discovery sets R to 1. If R is 1,
the receiving LSR checks whether it has been configured to send the receiving LSR checks whether it has been configured to send
Targeted Hellos to the Hello source in response to Hellos with Targeted Hellos to the Hello source in response to Hellos with
this request. If not, it ignores the request. If so, it ini- this request. If not, it ignores the request. If so, it
tiates periodic transmission of Targeted Hellos to the Hello initiates periodic transmission of Targeted Hellos to the Hello
source. source.
Reserved Reserved
This field is reserved. It MUST be set to zero on transmission This field is reserved. It MUST be set to zero on transmission
and ignored on receipt. and ignored on receipt.
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field of the Hello message contains 0 or more
encoded as a TLV. The optional parameters defined by this ver- parameters, each encoded as a TLV. The optional parameters
sion of the protocol are defined by this version of the protocol are
Optional Parameter Type Length Value Optional Parameter Type Length Value
IPv4 Transport Address 0x0401 4 See below IPv4 Transport Address 0x0401 4 See below
Configuration 0x0402 4 See below Configuration 0x0402 4 See below
Sequence Number Sequence Number
IPv6 Transport Address 0x0403 16 See below IPv6 Transport Address 0x0403 16 See below
IPv4 Transport Address IPv4 Transport Address
Specifies the IPv4 address to be used for the sending LSR when Specifies the IPv4 address to be used for the sending LSR when
opening the LDP session TCP connection. If this optional TLV opening the LDP session TCP connection. If this optional TLV
is not present the IPv4 source address for the UDP packet car- is not present, the IPv4 source address for the UDP packet
rying the Hello SHOULD be used. carrying the Hello SHOULD be used.
Configuration Sequence Number Configuration Sequence Number
Specifies a 4 octet unsigned configuration sequence number that Specifies a 4 octet unsigned configuration sequence number that
identifies the configuration state of the sending LSR. Used by identifies the configuration state of the sending LSR. Used by
the receiving LSR to detect configuration changes on the send- the receiving LSR to detect configuration changes on the
ing LSR. sending LSR.
IPv6 Transport Address IPv6 Transport Address
Specifies the IPv6 address to be used for the sending LSR when Specifies the IPv6 address to be used for the sending LSR when
opening the LDP session TCP connection. If this optional TLV opening the LDP session TCP connection. If this optional TLV
is not present the IPv6 source address for the UDP packet car- is not present the IPv6 source address for the UDP packet
rying the Hello SHOULD be used. carrying the Hello SHOULD be used.
3.5.2.1. Hello Message Procedures 3.5.2.1. Hello Message Procedures
An LSR receiving Hellos from another LSR maintains a Hello adjacency An LSR receiving Hellos from another LSR maintains a Hello adjacency
corresponding to the Hellos. The LSR maintains a hold timer with the corresponding to the Hellos. The LSR maintains a hold timer with the
Hello adjacency which it restarts whenever it receives a Hello that Hello adjacency, which it restarts whenever it receives a Hello that
matches the Hello adjacency. If the hold timer for a Hello adjacency matches the Hello adjacency. If the hold timer for a Hello adjacency
expires the LSR discards the Hello adjacency: see sections "Maintain- expires the LSR discards the Hello adjacency: see Sections
ing Hello Adjacencies" and "Maintaining LDP Sessions". "Maintaining Hello Adjacencies" and "Maintaining LDP Sessions".
We recommend that the interval between Hello transmissions be at most We recommend that the interval between Hello transmissions be at most
one third of the Hello hold time. one third of the Hello hold time.
An LSR processes a received LDP Hello as follows: An LSR processes a received LDP Hello as follows:
1. The LSR checks whether the Hello is acceptable. The criteria 1. The LSR checks whether the Hello is acceptable. The criteria
for determining whether a Hello is acceptable are implementa- for determining whether a Hello is acceptable are
tion dependent (see below for example criteria). implementation dependent (see below for example criteria).
2. If the Hello is not acceptable, the LSR ignores it. 2. If the Hello is not acceptable, the LSR ignores it.
3. If the Hello is acceptable, the LSR checks whether it has a 3. If the Hello is acceptable, the LSR checks whether it has a
Hello adjacency for the Hello source. If so, it restarts the Hello adjacency for the Hello source. If so, it restarts the
hold timer for the Hello adjacency. If not it creates a Hello hold timer for the Hello adjacency. If not, it creates a Hello
adjacency for the Hello source and starts its hold timer. adjacency for the Hello source and starts its hold timer.
4. If the Hello carries any optional TLVs the LSR processes them 4. If the Hello carries any optional TLVs, the LSR processes them
(see below). (see below).
5. Finally, if the LSR has no LDP session for the label space 5. Finally, if the LSR has no LDP session for the label space
specified by the LDP identifier in the PDU header for the specified by the LDP Identifier in the PDU header for the
Hello, it follows the procedures of Section "LDP Session Estab- Hello, it follows the procedures of Section "LDP Session
lishment". Establishment".
The following are examples of acceptability criteria for Link and The following are examples of acceptability criteria for Link and
Targeted Hellos: Targeted Hellos:
A Link Hello is acceptable if the interface on which it was A Link Hello is acceptable if the interface on which it was
received has been configured for label switching. received has been configured for label switching.
A Targeted Hello from source address A is acceptable if either: A Targeted Hello from source address A is acceptable if either:
- The LSR has been configured to accept Targeted Hellos, or - The LSR has been configured to accept Targeted Hellos, or
skipping to change at page 56, line 40 skipping to change at page 54, line 30
- The LSR has been configured to send Targeted Hellos to A. - The LSR has been configured to send Targeted Hellos to A.
The following describes how an LSR processes Hello optional TLVs: The following describes how an LSR processes Hello optional TLVs:
Transport Address Transport Address
The LSR associates the specified transport address with the The LSR associates the specified transport address with the
Hello adjacency. Hello adjacency.
Configuration Sequence Number Configuration Sequence Number
The Configuration Sequence Number optional parameter is used by The Configuration Sequence Number optional parameter is used by
the sending LSR to signal configuration changes to the receiv- the sending LSR to signal configuration changes to the
ing LSR. When a receiving LSR playing the active role in LDP receiving LSR. When a receiving LSR playing the active role in
session establishment detects a change in the sending LSR con- LDP session establishment detects a change in the sending LSR
figuration, it may clear the session setup backoff delay, if configuration, it may clear the session setup backoff delay, if
any, associated with the sending LSR (see Section "Session Ini- any, associated with the sending LSR (see Section "Session
tialization"). Initialization").
A sending LSR using this optional parameter is responsible for A sending LSR using this optional parameter is responsible for
maintaining the configuration sequence number it transmits in maintaining the configuration sequence number it transmits in
Hello messages. Whenever there is a configuration change on Hello messages. Whenever there is a configuration change on
the sending LSR, it increments the configuration sequence num- the sending LSR, it increments the configuration sequence
ber. number.
3.5.3. Initialization Message 3.5.3. Initialization Message
The LDP Initialization Message is exchanged as part of the LDP ses- The LDP Initialization message is exchanged as part of the LDP
sion establishment procedure; see Section "LDP Session Establish- session establishment procedure; see Section "LDP Session
ment". Establishment".
The encoding for the Initialization Message is: The encoding for the Initialization message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Initialization (0x0200) | Message Length | |0| Initialization (0x0200) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Session Parameters TLV | | Common Session Parameters TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 57, line 50 skipping to change at page 55, line 44
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|D| Reserved | PVLim | Max PDU Length | |A|D| Reserved | PVLim | Max PDU Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver LDP Identifier | | Receiver LDP Identifier |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++ -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
Protocol Version Protocol Version
Two octet unsigned integer containing the version number of the Two octet unsigned integer containing the version number of the
protocol. This version of the specification specifies LDP pro- protocol. This version of the specification specifies LDP
tocol version 1. protocol version 1.
KeepAlive Time KeepAlive Time
Two octet unsigned non zero integer that indicates the number Two octet unsigned non zero integer that indicates the number
of seconds that the sending LSR proposes for the value of the of seconds that the sending LSR proposes for the value of the
KeepAlive Time. The receiving LSR MUST calculate the value of KeepAlive Time. The receiving LSR MUST calculate the value of
the KeepAlive Timer by using the smaller of its proposed the KeepAlive Timer by using the smaller of its proposed
KeepAlive Time and the KeepAlive Time received in the PDU. The KeepAlive Time and the KeepAlive Time received in the PDU. The
value chosen for KeepAlive Time indicates the maximum number of value chosen for KeepAlive Time indicates the maximum number of
seconds that may elapse between the receipt of successive PDUs seconds that may elapse between the receipt of successive PDUs
from the LDP peer on the session TCP connection. The KeepAlive from the LDP peer on the session TCP connection. The KeepAlive
Timer is reset each time a PDU arrives. Timer is reset each time a PDU arrives.
A, Label Advertisement Discipline A, Label Advertisement Discipline
Indicates the type of Label advertisement. A value of 0 means Indicates the type of Label advertisement. A value of 0 means
Downstream Unsolicited advertisement; a value of 1 means Down- Downstream Unsolicited advertisement; a value of 1 means
stream On Demand. Downstream On Demand.
If one LSR proposes Downstream Unsolicited and the other pro- If one LSR proposes Downstream Unsolicited and the other
poses Downstream on Demand, the rules for resolving this dif- proposes Downstream on Demand, the rules for resolving this
ference is: difference is:
- If the session is for a label-controlled ATM link or a - If the session is for a label-controlled ATM link or a
label-controlled Frame Relay link, then Downstream on Demand label-controlled Frame Relay link, then Downstream on Demand
MUST be used. MUST be used.
- Otherwise, Downstream Unsolicited MUST be used. - Otherwise, Downstream Unsolicited MUST be used.
If the label advertisement discipline determined in this way is If the label advertisement discipline determined in this way
unacceptable to an LSR, it MUST send a Session Rejected/Parame- is unacceptable to an LSR, it MUST send a Session
ters Advertisement Mode Notification message in response to the Rejected/Parameters Advertisement Mode Notification message
Initialization message and not establish the session. in response to the Initialization message and not establish
the session.
D, Loop Detection D, Loop Detection
Indicates whether loop detection based on path vectors is Indicates whether Loop Detection based on Path Vectors is
enabled. A value of 0 means loop detection is disabled; a enabled. A value of 0 means that Loop Detection is disabled; a
value of 1 means that loop detection is enabled. value of 1 means that Loop Detection is enabled.
PVLim, Path Vector Limit PVLim, Path Vector Limit
The configured maximum path vector length. MUST be 0 if loop The configured maximum Path Vector length. MUST be 0 if Loop
detection is disabled (D = 0). If the loop detection proce- Detection is disabled (D = 0). If the Loop Detection
dures would require the LSR to send a path vector that exceeds procedures would require the LSR to send a Path Vector that
this limit, the LSR will behave as if a loop had been detected exceeds this limit, the LSR will behave as if a loop had been
for the FEC in question. detected for the FEC in question.
When Loop Detection is enabled in a portion of a network, it is When Loop Detection is enabled in a portion of a network, it is
recommended that all LSRs in that portion of the network be recommended that all LSRs in that portion of the network be
configured with the same path vector limit. Although knowledge configured with the same Path Vector limit. Although knowledge
of a peer's path vector limit will not change an LSR's behav- of a peer's Path Vector limit will not change an LSR's
ior, it does enable the LSR to alert an operator to a possible behavior, it does enable the LSR to alert an operator to a
misconfiguration. possible misconfiguration.
Reserved Reserved
This field is reserved. It MUST be set to zero on transmission This field is reserved. It MUST be set to zero on transmission
and ignored on receipt. and ignored on receipt.
Max PDU Length Max PDU Length
Two octet unsigned integer that proposes the maximum allowable Two octet unsigned integer that proposes the maximum allowable
length for LDP PDUs for the session. A value of 255 or less length for LDP PDUs for the session. A value of 255 or less
specifies the default maximum length of 4096 octets. specifies the default maximum length of 4096 octets.
skipping to change at page 59, line 27 skipping to change at page 57, line 22
for Max PDU Length. The default maximum PDU length applies for Max PDU Length. The default maximum PDU length applies
before session initialization completes. before session initialization completes.
If the maximum PDU length determined this way is unacceptable If the maximum PDU length determined this way is unacceptable
to an LSR, it MUST send a Session Rejected/Parameters Max PDU to an LSR, it MUST send a Session Rejected/Parameters Max PDU
Length Notification message in response to the Initialization Length Notification message in response to the Initialization
message and not establish the session. message and not establish the session.
Receiver LDP Identifier Receiver LDP Identifier
Identifies the receiver's label space. This LDP Identifier, Identifies the receiver's label space. This LDP Identifier,
together with the sender's LDP Identifier in the PDU header together with the sender's LDP Identifier in the PDU header,
enables the receiver to match the Initialization message with enables the receiver to match the Initialization message with
one of its Hello adjacencies; see Section "Hello Message Proce- one of its Hello adjacencies; see Section "Hello Message
dures". Procedures".
If there is no matching Hello adjacency, the LSR MUST send a If there is no matching Hello adjacency, the LSR MUST send a
Session Rejected/No Hello Notification message in response to Session Rejected/No Hello Notification message in response to
the Initialization message and not establish the session. the Initialization message and not establish the session.
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are: encoded as a TLV. The optional parameters are:
Optional Parameter Type Length Value Optional Parameter Type Length Value
skipping to change at page 60, line 39 skipping to change at page 58, line 43
1 VP Merge supported 1 VP Merge supported
2 VC Merge supported 2 VC Merge supported
3 VP & VC Merge supported 3 VP & VC Merge supported
If the merge capabilities of the LSRs differ, then: If the merge capabilities of the LSRs differ, then:
- Non-merge and VC-merge LSRs may freely interoperate. - Non-merge and VC-merge LSRs may freely interoperate.
- The interoperability of VP-merge-capable switches with non- - The interoperability of VP-merge-capable switches with non-
VP-merge-capable switches is a subject for future study. VP-merge-capable switches is a subject for future study.
When the LSRs differ on the use of VP-merge, the session is When the LSRs differ on the use of VP merge, the session is
established, but VP merge is not used. established, but VP merge is not used.
Note that if VP merge is used, it is the responsibility of the Note that if VP merge is used, it is the responsibility of the
ingress node to ensure that the chosen VCI is unique within the ingress node to ensure that the chosen VCI is unique within the
LSR domain. LSR domain.
N, Number of label range components N, Number of label range components
Specifies the number of ATM Label Range Components included in Specifies the number of ATM Label Range Components included in
the TLV. the TLV.
D, VC Directionality D, VC Directionality
A value of 0 specifies bidirectional VC capability, meaning the A value of 0 specifies bidirectional VC capability, meaning the
LSR can (within a given VPI) support the use of a given VCI as LSR can (within a given VPI) support the use of a given VCI as
a label for both link directions independently. A value of 1 a label for both link directions independently. A value of 1
specifies unidirectional VC capability, meaning (within a given specifies unidirectional VC capability, meaning (within a given
VPI) a given VCI may appear in a label mapping for one direc- VPI) a given VCI may appear in a label mapping for one
tion on the link only. When either or both of the peers speci- direction on the link only. When either or both of the peers
fies unidirectional VC capability, both LSRs use unidirectional specifies unidirectional VC capability, both LSRs use
VC label assignment for the link as follows. The LSRs compare unidirectional VC label assignment for the link as follows.
their LDP Identifiers as unsigned integers. The LSR with the The LSRs compare their LDP Identifiers as unsigned integers.
larger LDP Identifier may assign only odd-numbered VCIs in the The LSR with the larger LDP Identifier may assign only odd-
VPI/VCI range as labels. The system with the smaller LDP Iden- numbered VCIs in the VPI/VCI range as labels. The system with
tifier may assign only even-numbered VCIs in the VPI/VCI range the smaller LDP Identifier may assign only even-numbered VCIs
as labels. in the VPI/VCI range as labels.
Reserved Reserved
This field is reserved. It MUST be set to zero on transmission This field is reserved. It MUST be set to zero on transmission
and ignored on receipt. and ignored on receipt.
One or more ATM Label Range Components One or more ATM Label Range Components
A list of ATM Label Range Components which together specify the A list of ATM Label Range Components that together specify the
Label range supported by the transmitting LSR. Label range supported by the transmitting LSR.
A receiving LSR MUST calculate the intersection between the A receiving LSR MUST calculate the intersection between the
received range and its own supported label range. The inter- received range and its own supported label range. The
section is the range in which the LSR may allocate and accept intersection is the range in which the LSR may allocate and
labels. LSRs MUST NOT establish a session with neighbors for accept labels. LSRs MUST NOT establish a session with
which the intersection of ranges is NULL. In this case, the neighbors for which the intersection of ranges is NULL. In
LSR MUST send a Session Rejected/Parameters Label Range Notifi- this case, the LSR MUST send a Session Rejected/Parameters
cation message in response to the Initialization message and Label Range Notification message in response to the
not establish the session. Initialization message and not establish the session.
The encoding for an ATM Label Range Component is: The encoding for an ATM Label Range Component is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Minimum VPI | Minimum VCI | | Res | Minimum VPI | Minimum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Maximum VPI | Maximum VCI | | Res | Maximum VPI | Maximum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Res Res
This field is reserved. It MUST be set to zero on transmis- This field is reserved. It MUST be set to zero on
sion and MUST be ignored on receipt. transmission and MUST be ignored on receipt.
Minimum VPI (12 bits) Minimum VPI (12 bits)
This 12 bit field specifies the lower bound of a block of This 12-bit field specifies the lower bound of a block of
Virtual Path Identifiers that is supported on the originat- Virtual Path Identifiers that is supported on the
ing switch. If the VPI is less than 12-bits it SHOULD be originating switch. If the VPI is less than 12 bits, it
right justified in this field and preceding bits SHOULD be SHOULD be right justified in this field and preceding bits
set to 0. SHOULD be set to 0.
Minimum VCI (16 bits) Minimum VCI (16 bits)
This 16 bit field specifies the lower bound of a block of This 16-bit field specifies the lower bound of a block of
Virtual Connection Identifiers that is supported on the Virtual Channel Identifiers that is supported on the
originating switch. If the VCI is less than 16-bits it originating switch. If the VCI is less than 16 bits, it
SHOULD be right justified in this field and preceding bits SHOULD be right justified in this field and preceding bits
SHOULD be set to 0. SHOULD be set to 0.
Maximum VPI (12 bits) Maximum VPI (12 bits)
This 12 bit field specifies the upper bound of a block of This 12-bit field specifies the upper bound of a block of
Virtual Path Identifiers that is supported on the originat- Virtual Path Identifiers that is supported on the
ing switch. If the VPI is less than 12-bits it SHOULD be originating switch. If the VPI is less than 12 bits, it
right justified in this field and preceding bits SHOULD be SHOULD be right justified in this field and preceding bits
set to 0. SHOULD be set to 0.
Maximum VCI (16 bits) Maximum VCI (16 bits)
This 16 bit field specifies the upper bound of a block of This 16-bit field specifies the upper bound of a block of
Virtual Connection Identifiers that is supported on the Virtual Connection Identifiers that is supported on the
originating switch. If the VCI is less than 16-bits it originating switch. If the VCI is less than 16 bits, it
SHOULD be right justified in this field and preceding bits SHOULD be right justified in this field and preceding bits
SHOULD be set to 0. SHOULD be set to 0.
When peer LSRs are connected indirectly by means of an ATM VP, the When peer LSRs are connected indirectly by means of an ATM VP, the
sending LSR SHOULD set the Minimum and Maximum VPI fields to 0, sending LSR SHOULD set the Minimum and Maximum VPI fields to 0,
and the receiving LSR MUST ignore the Minimum and Maximum VPI and the receiving LSR MUST ignore the Minimum and Maximum VPI
fields. fields.
Frame Relay Session Parameters Frame Relay Session Parameters
Used when an LDP session manages label exchange for a Frame Used when an LDP session manages label exchange for a Frame
skipping to change at page 63, line 23 skipping to change at page 61, line 23
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Relay Label Range Component N | | Frame Relay Label Range Component N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M, Frame Relay Merge Capabilities M, Frame Relay Merge Capabilities
Specifies the merge capabilities of a Frame Relay switch. The Specifies the merge capabilities of a Frame Relay switch. The
following values are supported in this version of the specifi- following values are supported in this version of the
cation: specification:
Value Meaning Value Meaning
0 Merge not supported 0 Merge not supported
1 Merge supported 1 Merge supported
Non-merge and merge Frame Relay LSRs may freely interoperate. Non-merge and merge Frame Relay LSRs may freely interoperate.
N, Number of label range components Specifies the number of Frame N, Number of label range components
Relay Label Range Components included in the TLV. Specifies the number of Frame Relay Label Range Components
included in the TLV.
D, VC Directionality D, VC Directionality
A value of 0 specifies bidirectional VC capability, meaning the A value of 0 specifies bidirectional VC capability, meaning the
LSR can support the use of a given DLCI as a label for both LSR can support the use of a given DLCI as a label for both
link directions independently. A value of 1 specifies unidi- link directions independently. A value of 1 specifies
rectional VC capability, meaning a given DLCI may appear in a unidirectional VC capability, meaning a given DLCI may appear
label mapping for one direction on the link only. When either in a label mapping for one direction on the link only. When
or both of the peers specifies unidirectional VC capability, either or both of the peers specifies unidirectional VC
both LSRs use unidirectional VC label assignment for the link capability, both LSRs use unidirectional VC label assignment
as follows. The LSRs compare their LDP Identifiers as unsigned for the link as follows. The LSRs compare their LDP
integers. The LSR with the larger LDP Identifier may assign Identifiers as unsigned integers. The LSR with the larger LDP
only odd-numbered DLCIs in the range as labels. The system Identifier may assign only odd-numbered DLCIs in the range as
with the smaller LDP Identifier may assign only even-numbered labels. The system with the smaller LDP Identifier may assign
DLCIs in the range as labels. only even-numbered DLCIs in the range as labels.
Reserved Reserved
This field is reserved. It MUST be set to zero on transmission This field is reserved. It MUST be set to zero on transmission
and ignored on receipt. and ignored on receipt.
One or more Frame Relay Label Range Components One or more Frame Relay Label Range Components
A list of Frame Relay Label Range Components which together A list of Frame Relay Label Range Components that together
specify the Label range supported by the transmitting LSR. specify the Label range supported by the transmitting LSR.
A receiving LSR MUST calculate the intersection between the A receiving LSR MUST calculate the intersection between the
received range and its own supported label range. The inter- received range and its own supported label range. The
section is the range in which the LSR may allocate and accept intersection is the range in which the LSR may allocate and
labels. LSRs MUST NOT establish a session with neighbors for accept labels. LSRs MUST NOT establish a session with
which the intersection of ranges is NULL. In this case, the neighbors for which the intersection of ranges is NULL. In
LSR MUST send a Session Rejected/Parameters Label Range Notifi- this case, the LSR MUST send a Session Rejected/Parameters
cation message in response to the Initialization message and Label Range Notification message in response to the
not establish the session. Initialization message and not establish the session.
The encoding for a Frame Relay Label Range Component is: The encoding for a Frame Relay Label Range Component is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Len| Minimum DLCI | | Reserved |Len| Minimum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Maximum DLCI | | Reserved | Maximum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved Reserved
This field is reserved. It MUST be set to zero on transmis- This field is reserved. It MUST be set to zero on transmission
sion and ignored on receipt. and ignored on receipt.
Len Len
This field specifies the number of bits of the DLCI. The This field specifies the number of bits of the DLCI. The
following values are supported: following values are supported:
Len DLCI bits Len DLCI Bits
0 10 0 10
2 23 2 23
Len values 1 and 3 are reserved. Len values 1 and 3 are reserved.
Minimum DLCI Minimum DLCI
This 23-bit field specifies the lower bound of a block of This 23-bit field specifies the lower bound of a block of Data
Data Link Connection Identifiers (DLCIs) that is supported Link Connection Identifiers (DLCIs) that is supported on the
on the originating switch. The DLCI SHOULD be right justi- originating switch. The DLCI SHOULD be right justified in this
fied in this field and unused bits SHOULD be set to 0. field and unused bits SHOULD be set to 0.
Maximum DLCI Maximum DLCI
This 23-bit field specifies the upper bound of a block of This 23-bit field specifies the upper bound of a block of Data
Data Link Connection Identifiers (DLCIs) that is supported Link Connection Identifiers (DLCIs) that is supported on the
on the originating switch. The DLCI SHOULD be right originating switch. The DLCI SHOULD be right justified in this
justified in this field and unused bits SHOULD be set to 0. field and unused bits SHOULD be set to 0.
Note that there is no Generic Session Parameters TLV for sessions Note that there is no Generic Session Parameters TLV for sessions
which advertise Generic Labels. that advertise Generic Labels.
3.5.3.1. Initialization Message Procedures 3.5.3.1. Initialization Message Procedures
See Section "LDP Session Establishment" and particularly Section See Section "LDP Session Establishment" and particularly Section
"Session Initialization" for general procedures for handling the Ini- "Session Initialization" for general procedures for handling the
tialization Message. Initialization message.
3.5.4. KeepAlive Message 3.5.4. KeepAlive Message
An LSR sends KeepAlive Messages as part of a mechanism that monitors An LSR sends KeepAlive messages as part of a mechanism that monitors
the integrity of the LDP session transport connection. the integrity of the LDP session transport connection.
The encoding for the KeepAlive Message is: The encoding for the KeepAlive message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| KeepAlive (0x0201) | Message Length | |0| KeepAlive (0x0201) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
Optional Parameters Optional Parameters
No optional parameters are defined for the KeepAlive message. No optional parameters are defined for the KeepAlive message.
3.5.4.1. KeepAlive Message Procedures 3.5.4.1. KeepAlive Message Procedures
The KeepAlive Timer mechanism described in Section "Maintaining LDP The KeepAlive Timer mechanism described in Section "Maintaining LDP
Sessions" resets a session KeepAlive timer every time an LDP PDU is Sessions" resets a session KeepAlive Timer every time an LDP PDU is
received on the session TCP connection. The KeepAlive Message is received on the session TCP connection. The KeepAlive message is
provided to allow reset of the KeepAlive Timer in circumstances where provided to allow reset of the KeepAlive Timer in circumstances where
an LSR has no other information to communicate to an LDP peer. an LSR has no other information to communicate to an LDP peer.
An LSR MUST arrange that its peer receive an LDP Message from it at An LSR MUST arrange that its peer receive an LDP message from it at
least every KeepAlive Time period. Any LDP protocol message will do least every KeepAlive Time period. Any LDP protocol message will do
but, in circumstances where no other LDP protocol messages have been but, in circumstances where no other LDP protocol messages have been
sent within the period, a KeepAlive message MUST be sent. sent within the period, a KeepAlive message MUST be sent.
3.5.5. Address Message 3.5.5. Address Message
An LSR sends the Address Message to an LDP peer to advertise its An LSR sends the Address message to an LDP peer to advertise its
interface addresses. interface addresses.
The encoding for the Address Message is: The encoding for the Address message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Address (0x0300) | Message Length | |0| Address (0x0300) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Address List TLV | | Address List TLV |
skipping to change at page 66, line 40 skipping to change at page 64, line 41
Address List TLV Address List TLV
The list of interface addresses being advertised by the sending The list of interface addresses being advertised by the sending
LSR. The encoding for the Address List TLV is specified in LSR. The encoding for the Address List TLV is specified in
Section "Address List TLV". Section "Address List TLV".
Optional Parameters Optional Parameters
No optional parameters are defined for the Address message. No optional parameters are defined for the Address message.
3.5.5.1. Address Message Procedures 3.5.5.1. Address Message Procedures
An LSR that receives an Address Message message uses the addresses it An LSR that receives an Address message uses the addresses it learns
learns to maintain a database for mapping between peer LDP Identi- to maintain a database for mapping between peer LDP Identifiers and
fiers and next hop addresses; see Section "LDP Identifiers and Next next hop addresses; see Section "LDP Identifiers and Next Hop
Hop Addresses". Addresses".
When a new LDP session is initialized and before sending Label Map- When a new LDP session is initialized and before sending Label
ping or Label Request messages an LSR SHOULD advertise its interface Mapping or Label Request messages, an LSR SHOULD advertise its
addresses with one or more Address messages. interface addresses with one or more Address messages.
Whenever an LSR "activates" a new interface address, it SHOULD Whenever an LSR "activates" a new interface address, it SHOULD
advertise the new address with an Address message. advertise the new address with an Address message.
Whenever an LSR "de-activates" a previously advertised address, it Whenever an LSR "de-activates" a previously advertised address, it
SHOULD withdraw the address with an Address Withdraw message; see SHOULD withdraw the address with an Address Withdraw message; see
Section "Address Withdraw Message". Section "Address Withdraw Message".
If an LSR does not support the Address Family specified in the If an LSR does not support the Address Family specified in the
Address List TLV, it SHOULD send an "Unsupported Address Family" Address List TLV, it SHOULD send an Unsupported Address Family
Notification to its LDP signalling an error and abort processing the Notification to its LDP signaling an error and abort processing the
message. message.
An LSR may re-advertise an address (A) that it has previously adver- An LSR may re-advertise an address (A) that it has previously
tised without explicitly withdrawing the address. If the receiver advertised without explicitly withdrawing the address. If the
already has address binding (LSR, A) it SHOULD take no further receiver already has address binding (LSR, A), it SHOULD take no
action. further action.
An LSR may withdraw an address (A) without having previously adver- An LSR may withdraw an address (A) without having previously
tised it. If the receiver has no address binding (LSR, A), it SHOULD advertised it. If the receiver has no address binding (LSR, A), it
take no further action. SHOULD take no further action.
3.5.6. Address Withdraw Message 3.5.6. Address Withdraw Message
An LSR sends the Address Withdraw Message to an LDP peer to withdraw An LSR sends the Address Withdraw message to an LDP peer to withdraw
previously advertised interface addresses. previously advertised interface addresses.
The encoding for the Address Withdraw Message is: The encoding for the Address Withdraw message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Address Withdraw (0x0301) | Message Length | |0| Address Withdraw (0x0301) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Address List TLV | | Address List TLV |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
Address list TLV Address List TLV
The list of interface addresses being withdrawn by the sending The list of interface addresses being withdrawn by the sending
LSR. The encoding for the Address list TLV is specified in LSR. The encoding for the Address List TLV is specified in
Section "Address List TLV". Section "Address List TLV".
Optional Parameters Optional Parameters
No optional parameters are defined for the Address Withdraw mes- No optional parameters are defined for the Address Withdraw
sage. message.
3.5.6.1. Address Withdraw Message Procedures 3.5.6.1. Address Withdraw Message Procedures
See Section "Address Message Procedures" See Section "Address Message Procedures".
3.5.7. Label Mapping Message 3.5.7. Label Mapping Message
An LSR sends a Label Mapping message to an LDP peer to advertise FEC- An LSR sends a Label Mapping message to an LDP peer to advertise
label bindings to the peer. FEC-label bindings to the peer.
The encoding for the Label Mapping Message is: The encoding for the Label Mapping message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Mapping (0x0400) | Message Length | |0| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV | | Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
FEC TLV FEC TLV
Specifies the FEC component of the FEC-Label mapping being adver- Specifies the FEC component of the FEC-Label mapping being
tised. See Section "FEC TLV" for encoding. advertised. See Section "FEC TLVs" for encoding.
Label TLV Label TLV
Specifies the Label component of the FEC-Label mapping. See Sec- Specifies the Label component of the FEC-Label mapping. See
tion "Label TLV" for encoding. Section "Label TLV" for encoding.
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are: encoded as a TLV. The optional parameters are:
Optional Parameter Length Value Optional Parameter Length Value
Label Request 4 See below Label Request 4 See below
Message ID TLV Message ID TLV
Hop Count TLV 1 See below Hop Count TLV 1 See below
Path Vector TLV variable See below Path Vector TLV variable See below
The encodings for the Hop Count, and Path Vector TLVs can be found The encodings for the Hop Count and Path Vector TLVs can be found
in Section "TLV Encodings for Commonly Used Parameters". in Section "TLV Encodings for Commonly Used Parameters".
Label Request Message ID Label Request Message ID
If this Label Mapping message is a response to a Label Request If this Label Mapping message is a response to a Label Request
message it MUST include the Request Message Id optional parame- message, it MUST include the Label Request Message ID optional
ter. The value of this optional parameter is the Message Id of parameter. The value of this optional parameter is the Message
the corresponding Label Request Message. ID of the corresponding Label Request message.
Hop Count Hop Count
Specifies the running total of the number of LSR hops along the Specifies the running total of the number of LSR hops along the
LSP being setup by the Label Message. Section "Hop Count Pro- LSP being set up by the Label message. Section "Hop Count
cedures" describes how to handle this TLV. Procedures" describes how to handle this TLV.
Path Vector Path Vector
Specifies the LSRs along the LSP being setup by the Label Mes- Specifies the LSRs along the LSP being set up by the Label
sage. Section "Path Vector Procedures" describes how to handle message. Section "Path Vector Procedures" describes how to
this TLV. handle this TLV.
3.5.7.1. Label Mapping Message Procedures 3.5.7.1. Label Mapping Message Procedures
The Mapping message is used by an LSR to distribute a label mapping The Mapping message is used by an LSR to distribute a label mapping
for a FEC to an LDP peer. If an LSR distributes a mapping for a FEC for a FEC to an LDP peer. If an LSR distributes a mapping for a FEC
to multiple LDP peers, it is a local matter whether it maps a single to multiple LDP peers, it is a local matter whether it maps a single
label to the FEC, and distributes that mapping to all its peers, or label to the FEC, and distributes that mapping to all its peers, or
whether it uses a different mapping for each of its peers. whether it uses a different mapping for each of its peers.
An LSR is responsible for the consistency of the label mappings it An LSR is responsible for the consistency of the label mappings it
has distributed, and that its peers have these mappings. has distributed and that its peers have these mappings.
An LSR receiving a Label Mapping message from a downstream LSR for a An LSR receiving a Label Mapping message from a downstream LSR for a
Prefix SHOULD NOT use the label for forwarding unless its routing ta- Prefix SHOULD NOT use the label for forwarding unless its routing
ble contains an entry that exactly matches the FEC Element. table contains an entry that exactly matches the FEC Element.
See Appendix A "LDP Label Distribution Procedures" for more details. See Appendix A, "LDP Label Distribution Procedures", for more
details.
3.5.7.1.1. Independent Control Mapping 3.5.7.1.1. Independent Control Mapping
If an LSR is configured for independent control, a mapping message is If an LSR is configured for independent control, a mapping message is
transmitted by the LSR upon any of the following conditions: transmitted by the LSR upon any of the following conditions:
1. The LSR recognizes a new FEC via the forwarding table, and the 1. The LSR recognizes a new FEC via the forwarding table, and the
label advertisement mode is Downstream Unsolicited advertise- label advertisement mode is Downstream Unsolicited
ment. advertisement.
2. The LSR receives a Request message from an upstream peer for a 2. The LSR receives a Request message from an upstream peer for a
FEC present in the LSR's forwarding table. FEC present in the LSR's forwarding table.
3. The next hop for a FEC changes to another LDP peer, and loop 3. The next hop for a FEC changes to another LDP peer, and Loop
detection is configured. detection is configured.
4. The attributes of a mapping change. 4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND 5. The receipt of a mapping from the downstream next hop AND
a) no upstream mapping has been created OR a) no upstream mapping has been created OR
b) loop detection is configured OR b) loop detection is configured OR
c) the attributes of the mapping have changed. c) the attributes of the mapping have changed.
3.5.7.1.2. Ordered Control Mapping 3.5.7.1.2. Ordered Control Mapping
If an LSR is doing ordered control, a Mapping message is transmitted If an LSR is doing Ordered Control, a Mapping message is transmitted
by downstream LSRs upon any of the following conditions: by downstream LSRs upon any of the following conditions:
1. The LSR recognizes a new FEC via the forwarding table, and is 1. The LSR recognizes a new FEC via the forwarding table and is
the egress for that FEC. the egress for that FEC.
2. The LSR receives a Request message from an upstream peer for a 2. The LSR receives a Request message from an upstream peer for a
FEC present in the LSR's forwarding table, and the LSR is the FEC present in the LSR's forwarding table, and the LSR is the
egress for that FEC OR has a downstream mapping for that FEC. egress for that FEC OR has a downstream mapping for that FEC.
3. The next hop for a FEC changes to another LDP peer, and loop 3. The next hop for a FEC changes to another LDP peer, and Loop
detection is configured. Detection is configured.
4. The attributes of a mapping change. 4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND 5. The receipt of a mapping from the downstream next hop AND
a) no upstream mapping has been created OR a) no upstream mapping has been created OR
b) loop detection is configured OR b) Loop Detection is configured OR
c) the attributes of the mapping have changed. c) the attributes of the mapping have changed.
3.5.7.1.3. Downstream on Demand Label Advertisement 3.5.7.1.3. Downstream on Demand Label Advertisement
In general, the upstream LSR is responsible for requesting label map- In general, the upstream LSR is responsible for requesting label
pings when operating in Downstream on Demand mode. However, unless mappings when operating in Downstream on Demand mode. However,
some rules are followed, it is possible for neighboring LSRs with unless some rules are followed, it is possible for neighboring LSRs
different advertisement modes to get into a livelock situation where with different advertisement modes to get into a livelock situation
everything is functioning properly, but no labels are distributed. where everything is functioning properly, but no labels are
For example, consider two LSRs Ru and Rd where Ru is the upstream LSR distributed. For example, consider two LSRs Ru and Rd where Ru is
and Rd is the downstream LSR for a particular FEC. In this example, the upstream LSR and Rd is the downstream LSR for a particular FEC.
Ru is using Downstream Unsolicited advertisement mode and Rd is using In this example, Ru is using Downstream Unsolicited advertisement
Downstream on Demand mode. In this case, Rd may assume that Ru will mode and Rd is using Downstream on Demand mode. In this case, Rd may
request a label mapping when it wants one and Ru may assume that Rd assume that Ru will request a label mapping when it wants one and Ru
will advertise a label if it wants Ru to use one. If Rd and Ru oper- may assume that Rd will advertise a label if it wants Ru to use one.
ate as suggested, no labels will be distributed from Rd to Ru. If Rd and Ru operate as suggested, no labels will be distributed from
Rd to Ru.
This livelock situation can be avoided if the following rule is This livelock situation can be avoided if the following rule is
observed: an LSR operating in Downstream on Demand mode SHOULD NOT be observed: an LSR operating in Downstream on Demand mode SHOULD NOT be
expected to send unsolicited mapping advertisements. Therefore, if expected to send unsolicited mapping advertisements. Therefore, if
the downstream LSR is operating in Downstream on Demand mode, the the downstream LSR is operating in Downstream on Demand mode, the
upstream LSR is responsible for requesting label mappings as needed. upstream LSR is responsible for requesting label mappings as needed.
3.5.7.1.4. Downstream Unsolicited Label Advertisement 3.5.7.1.4. Downstream Unsolicited Label Advertisement
In general, the downstream LSR is responsible for advertising a label In general, the downstream LSR is responsible for advertising a label
mapping when it wants an upstream LSR to use the label. An upstream mapping when it wants an upstream LSR to use the label. An upstream
LSR may issue a mapping request if it so desires. LSR may issue a mapping request if it so desires.
The combination of Downstream Unsolicited mode and conservative label The combination of Downstream Unsolicited mode and Conservative Label
retention can lead to a situation where an LSR releases the label for retention can lead to a situation where an LSR releases the label for
a FEC that it later needs. For example, if LSR Rd advertises to LSR a FEC that it later needs. For example, if LSR Rd advertises to LSR
Ru the label for a FEC for which it is not Ru's next hop, Ru will Ru the label for a FEC for which it is not Ru's next hop, Ru will
release the label. If Ru's next hop for the FEC later changes to Rd, release the label. If Ru's next hop for the FEC later changes to Rd,
it needs the previously released label. it needs the previously released label.
To deal with this situation either Ru can explicitly request the To deal with this situation, either Ru can explicitly request the
label when it needs it, or Rd can periodically readvertise it to Ru. label when it needs it, or Rd can periodically re-advertise it to Ru.
In many situations Ru will know when it needs the label from Rd. For In many situations Ru will know when it needs the label from Rd. For
example, when its next hop for the FEC changes to Rd. However, there example, when its next hop for the FEC changes to Rd. However, there
could be situations when Ru does not. For example, Rd may be could be situations when Ru does not. For example, Rd may be
attempting to establish an LSP with non-standard properties. Forcing attempting to establish an LSP with non-standard properties. Forcing
Ru to explicitly request the label in this situation would require it Ru to explicitly request the label in this situation would require it
to maintain state about a potential LSP with non-standard properties. to maintain state about a potential LSP with non-standard properties.
In situations where Ru knows it needs the label, it is responsible In situations where Ru knows it needs the label, it is responsible
for explicitly requesting the label by means of a Label Request mes- for explicitly requesting the label by means of a Label Request
sage. In situations where Ru may not know that it needs the label, message. In situations where Ru may not know that it needs the
Rd is responsible for periodically readvertising the label to Ru. label, Rd is responsible for periodically re-advertising the label to
Ru.
For this version of LDP, the only situation where Ru knows it needs a For this version of LDP, the only situation where Ru knows it needs a
label for a FEC from Rd is when Rd is its next hop for the FEC, Ru label for a FEC from Rd is when Rd is its next hop for the FEC, Ru
does not have a label from Rd, and the LSP for the FEC is one that does not have a label from Rd, and the LSP for the FEC is one that
can be established with TLVs defined in this document. can be established with TLVs defined in this document.
3.5.8. Label Request Message 3.5.8. Label Request Message
An LSR sends the Label Request Message to an LDP peer to request a An LSR sends the Label Request message to an LDP peer to request a
binding (mapping) for a FEC. binding (mapping) for a FEC.
The encoding for the Label Request Message is: The encoding for the Label Request message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Request (0x0401) | Message Length | |0| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 72, line 45 skipping to change at page 70, line 40
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are: encoded as a TLV. The optional parameters are:
Optional Parameter Length Value Optional Parameter Length Value
Hop Count TLV 1 See below Hop Count TLV 1 See below
Path Vector TLV variable See below Path Vector TLV variable See below
The encodings for the Hop Count, and Path Vector TLVs can be found The encodings for the Hop Count and Path Vector TLVs can be found
in Section "TLV Encodings for Commonly Used Parameters". in Section "TLV Encodings for Commonly Used Parameters".
Hop Count Hop Count
Specifies the running total of the number of LSR hops along the Specifies the running total of the number of LSR hops along the
LSP being setup by the Label Request Message. Section "Hop LSP being set up by the Label Request message. Section "Hop Count
Count Procedures" describes how to handle this TLV. Procedures" describes how to handle this TLV.
Path Vector Path Vector
Specifies the LSRs along the LSR being setup by the Label Specifies the LSRs along the LSR being set up by the Label Request
Request Message. Section "Path Vector Procedures" describes message. Section "Path Vector Procedures" describes how to handle
how to handle this TLV. this TLV.
3.5.8.1. Label Request Message Procedures 3.5.8.1. Label Request Message Procedures
The Request message is used by an upstream LSR to explicitly request The Request message is used by an upstream LSR to explicitly request
that the downstream LSR assign and advertise a label for a FEC. that the downstream LSR assign and advertise a label for a FEC.
An LSR may transmit a Request message under any of the following con- An LSR may transmit a Request message under any of the following
ditions: conditions:
1. The LSR recognizes a new FEC via the forwarding table, and the 1. The LSR recognizes a new FEC via the forwarding table, and the
next hop is an LDP peer, and the LSR doesn't already have a next hop is an LDP peer, and the LSR doesn't already have a
mapping from the next hop for the given FEC. mapping from the next hop for the given FEC.
2. The next hop to the FEC changes, and the LSR doesn't already 2. The next hop to the FEC changes, and the LSR doesn't already
have a mapping from that next hop for the given FEC. have a mapping from that next hop for the given FEC.
Note that if the LSR already has a pending Label Request mes- Note that if the LSR already has a pending Label Request
sage for the new next hop it SHOULD NOT issue an additional message for the new next hop, it SHOULD NOT issue an additional
Label Request in response to the next hop change. Label Request in response to the next hop change.
3. The LSR receives a Label Request for a FEC from an upstream LDP 3. The LSR receives a Label Request for a FEC from an upstream LDP
peer, the FEC next hop is an LDP peer, and the LSR doesn't peer, the FEC next hop is an LDP peer, and the LSR doesn't
already have a mapping from the next hop. already have a mapping from the next hop.
Note that since a non-merge LSR must setup a separate LSP for Note that since a non-merge LSR must setup a separate LSP for
each upstream peer requesting a label, it must send a separate each upstream peer requesting a label, it must send a separate
Label Request for each such peer. A consequence of this is Label Request for each such peer. A consequence of this is
that a non-merge LSR may have multiple Label Request messages that a non-merge LSR may have multiple Label Request messages
skipping to change at page 74, line 4 skipping to change at page 71, line 47
When the FEC for which a label is requested is a Prefix FEC Element, When the FEC for which a label is requested is a Prefix FEC Element,
the receiving LSR uses its routing table to determine its response. the receiving LSR uses its routing table to determine its response.
Unless its routing table includes an entry that exactly matches the Unless its routing table includes an entry that exactly matches the
requested Prefix, the LSR MUST respond with a No Route Notification requested Prefix, the LSR MUST respond with a No Route Notification
message. message.
The message ID of the Label Request message serves as an identifier The message ID of the Label Request message serves as an identifier
for the Label Request transaction. When the receiving LSR responds for the Label Request transaction. When the receiving LSR responds
with a Label Mapping message, the mapping message MUST include a with a Label Mapping message, the mapping message MUST include a
Label Request/Returned Message ID TLV optional parameter which Label Request/Returned Message ID TLV optional parameter that
includes the message ID of the Label Request message. Note that includes the message ID of the Label Request message. Note that
since LSRs use Label Request message IDs as transaction identifiers since LSRs use Label Request message IDs as transaction identifiers,
an LSR SHOULD NOT reuse the message ID of a Label Request message an LSR SHOULD NOT reuse the message ID of a Label Request message
until the corresponding transaction completes. until the corresponding transaction completes.
This version of the protocol defines the following Status Codes for This version of the protocol defines the following Status Codes for
the Notification message that signals a request cannot be satisfied: the Notification message that signals a request cannot be satisfied:
No Route No Route
The FEC for which a label was requested includes a FEC Element The FEC for which a label was requested includes a FEC Element
for which the LSR does not have a route. for which the LSR does not have a route.
No Label Resources No Label Resources
The LSR cannot provide a label because of resource limitations. The LSR cannot provide a label because of resource limitations.
When resources become available the LSR MUST notify the When resources become available, the LSR MUST notify the
requesting LSR by sending a Notification message with the Label requesting LSR by sending a Notification message with the Label
Resources Available Status Code. Resources Available Status Code.
An LSR that receives a No Label Resources response to a Label An LSR that receives a No Label Resources response to a Label
Request message MUST NOT issue further Label Request messages Request message MUST NOT issue further Label Request messages
until it receives a Notification message with the Label until it receives a Notification message with the Label
Resources Available Status code. Resources Available Status Code.
Loop Detected Loop Detected
The LSR has detected a looping Label Request message. The LSR has detected a looping Label Request message.
See Appendix A "LDP Label Distribution Procedures" for more details. See Appendix A, "LDP Label Distribution Procedures", for more
details.
3.5.9. Label Abort Request Message 3.5.9. Label Abort Request Message
The Label Abort Request message may be used to abort an outstanding The Label Abort Request message may be used to abort an outstanding
Label Request message. Label Request message.
The encoding for the Label Abort Request Message is: The encoding for the Label Abort Request message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Abort Req (0x0404) | Message Length | |0| Label Abort Req (0x0404) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 75, line 30 skipping to change at page 73, line 13
32-bit value used to identify this message. 32-bit value used to identify this message.
FEC TLV FEC TLV
Identifies the FEC for which the Label Request is being aborted. Identifies the FEC for which the Label Request is being aborted.
Label Request Message ID TLV Label Request Message ID TLV
Specifies the message ID of the Label Request message to be Specifies the message ID of the Label Request message to be
aborted. aborted.
Optional Parameters Optional Parameters
No optional parameters are defined for the Label Abort Req mes- No optional parameters are defined for the Label Abort Req
sage. message.
3.5.9.1. Label Abort Request Message Procedures 3.5.9.1. Label Abort Request Message Procedures
An LSR Ru may send a Label Abort Request message to abort an out- An LSR Ru may send a Label Abort Request message to abort an
standing Label Request message for FEC sent to LSR Rd in the follow- outstanding Label Request message for a FEC sent to an LSR Rd in the
ing circumstances: following circumstances:
1. Ru's next hop for FEC has changed from LSR Rd to LSR X; or 1. Ru's next hop for the FEC has changed from LSR Rd to LSR X; or
2. Ru is a non-merge, non-ingress LSR and has received a Label 2. Ru is a non-merge, non-ingress LSR and has received a Label
Abort Request for FEC from an upstream peer Y. Abort Request for the FEC from an upstream peer Y.
3. Ru is a merge, non-ingress LSR and has received a Label Abort 3. Ru is a merge, non-ingress LSR and has received a Label Abort
Request for FEC from an upstream peer Y and Y is the only Request for the FEC from an upstream peer Y and Y is the only
(last) upstream LSR requesting a label for FEC. (last) upstream LSR requesting a label for the FEC.
There may be other situations where an LSR may choose to abort an There may be other situations where an LSR may choose to abort an
outstanding Label Request message in order to reclaim resource asso- outstanding Label Request message in order to reclaim resource
ciated with the pending LSP. However, specification of general associated with the pending LSP. However, specification of general
strategies for using the abort mechanism is beyond the scope of LDP. strategies for using the abort mechanism is beyond the scope of LDP.
When an LSR receives a Label Abort Request message, if it has not When an LSR receives a Label Abort Request message, if it has not
previously responded to the Label Request being aborted with a Label previously responded to the Label Request being aborted with a Label
Mapping message or some other Notification message, it MUST acknowl- Mapping message or some other Notification message, it MUST
edge the abort by responding with a Label Request Aborted Notifica- acknowledge the abort by responding with a Label Request Aborted
tion message. The Notification MUST include a Label Request Message Notification message. The Notification MUST include a Label Request
ID TLV that carries the message ID of the aborted Label Request mes- Message ID TLV that carries the message ID of the aborted Label
sage. Request message.
If an LSR receives a Label Abort Request Message after it has If an LSR receives a Label Abort Request Message after it has
responded to the Label Request in question with a Label Mapping mes- responded to the Label Request in question with a Label Mapping
sage or a Notification message, it ignores the abort request. message or a Notification message, it ignores the abort request.
If an LSR receives a Label Mapping message in response to a Label If an LSR receives a Label Mapping message in response to a Label
Request message after it has sent a Label Abort Request message to Request message after it has sent a Label Abort Request message to
abort the Label Request, the label in the Label Mapping message is abort the Label Request, the label in the Label Mapping message is
valid. The LSR may choose to use the label or to release it with a valid. The LSR may choose to use the label or to release it with a
Label Release message. Label Release message.
An LSR aborting a Label Request message may not reuse the Message ID An LSR aborting a Label Request message may not reuse the Message ID
for the Label Request message until it receives one of the following for the Label Request message until it receives one of the following
from its peer: from its peer:
- A Label Request Aborted Notification message acknowledging the - A Label Request Aborted Notification message acknowledging the
abort; abort;
- A Label Mapping message in response to the Label Request mes- - A Label Mapping message in response to the Label Request
sage being aborted; message being aborted;
- A Notification message in response to the Label Request message - A Notification message in response to the Label Request message
being aborted (e.g., Loop Detected, No Label Resources, etc.). being aborted (e.g., Loop Detected, No Label Resources, etc.).
To protect itself against tardy peers or faulty peer implementations To protect itself against tardy peers or faulty peer implementations
an LSR may choose to time out receipt of the above. The time out an LSR may choose to time out receipt of the above. The time out
period should be relatively long (several minutes). If the time out period should be relatively long (several minutes). If the time out
period elapses with no reply from the peer the LSR may reuse the Mes- period elapses with no reply from the peer, the LSR may reuse the
sage Id of the Label Request message; if it does so, it should also Message ID of the Label Request message; if it does so, it should
discard any record of the outstanding Label Request and Label Abort also discard any record of the outstanding Label Request and Label
messages. Abort messages.
Note that the response to a Label Abort Request message is never Note that the response to a Label Abort Request message is never
"ordered". That is, the response does not depend on the downstream "ordered". That is, the response does not depend on the downstream
state of the LSP setup being aborted. An LSR receiving a Label Abort state of the LSP setup being aborted. An LSR receiving a Label Abort
Request message MUST process it immediately, regardless of the down- Request message MUST process it immediately, regardless of the
stream state of the LSP, responding with a Label Request Aborted downstream state of the LSP, responding with a Label Request Aborted
Notification or ignoring it, as appropriate. Notification or ignoring it, as appropriate.
3.5.10. Label Withdraw Message 3.5.10. Label Withdraw Message
An LSR sends a Label Withdraw Message to an LDP peer to signal the An LSR sends a Label Withdraw Message to an LDP peer to signal the
peer that the peer may not continue to use specific FEC-label map- peer that the peer may not continue to use specific FEC-label
pings the LSR had previously advertised. This breaks the mapping mappings the LSR had previously advertised. This breaks the mapping
between the FECs and the labels. between the FECs and the labels.
The encoding for the Label Withdraw Message is: The encoding for the Label Withdraw Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Withdraw (0x0402) | Message Length | |0| Label Withdraw (0x0402) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
skipping to change at page 77, line 32 skipping to change at page 75, line 25
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) | | Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
FEC TLV FEC TLV
Identifies the FEC for which the FEC-label mapping is being with- Identifies the FEC for which the FEC-label mapping is being
drawn. withdrawn.
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are: encoded as a TLV. The optional parameters are:
Optional Parameter Length Value Optional Parameter Length Value
Label TLV variable See below Label TLV variable See below
The encoding for Label TLVs are found in Section "Label TLVs". The encoding for Label TLVs are found in Section "Label TLVs".
Label Label
If present, specifies the label being withdrawn (see procedures If present, specifies the label being withdrawn (see procedures
below). below).
3.5.10.1. Label Withdraw Message Procedures 3.5.10.1. Label Withdraw Message Procedures
An LSR transmits a Label Withdraw message under the following condi- An LSR transmits a Label Withdraw message under the following
tions: conditions:
1. The LSR no longer recognizes a previously known FEC for which 1. The LSR no longer recognizes a previously known FEC for which
it has advertised a label. it has advertised a label.
2. The LSR has decided unilaterally (e.g., via configuration) to 2. The LSR has decided unilaterally (e.g., via configuration) to
no longer label switch a FEC (or FECs) with the label mapping no longer label switch a FEC (or FECs) with the label mapping
being withdrawn. being withdrawn.
The FEC TLV specifies the FEC for which labels are to be withdrawn. The FEC TLV specifies the FEC for which labels are to be withdrawn.
If no Label TLV follows the FEC, all labels associated with the FEC If no Label TLV follows the FEC, all labels associated with the FEC
are to be withdrawn; otherwise only the label specified in the are to be withdrawn; otherwise, only the label specified in the
optional Label TLV is to be withdrawn. optional Label TLV is to be withdrawn.
The FEC TLV may contain the Wildcard FEC Element; if so, it may con- The FEC TLV may contain the Wildcard FEC Element; if so, it may
tain no other FEC Elements. In this case, if the Label Withdraw mes- contain no other FEC Elements. In this case, if the Label Withdraw
sage contains an optional Label TLV, then the label is to be with- message contains an optional Label TLV, then the label is to be
drawn from all FECs to which it is bound. If there is not an withdrawn from all FECs to which it is bound. If there is not an
optional Label TLV in the Label Withdraw message, then the sending optional Label TLV in the Label Withdraw message, then the sending
LSR is withdrawing all label mappings previously advertised to the LSR is withdrawing all label mappings previously advertised to the
receiving LSR. receiving LSR.
An LSR that receives a Label Withdraw message MUST respond with a An LSR that receives a Label Withdraw message MUST respond with a
Label Release message. Label Release message.
See Appendix A "LDP Label Distribution Procedures" for more details. See Appendix A, "LDP Label Distribution Procedures", for more
details.
3.5.11. Label Release Message 3.5.11. Label Release Message
An LSR sends a Label Release message to an LDP peer to signal the An LSR sends a Label Release message to an LDP peer to signal the
peer that the LSR no longer needs specific FEC-label mappings previ- peer that the LSR no longer needs specific FEC-label mappings
ously requested of and/or advertised by the peer. previously requested of and/or advertised by the peer.
The encoding for the Label Release Message is: The encoding for the Label Release Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Release (0x0403) | Message Length | |0| Label Release (0x0403) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 79, line 41 skipping to change at page 77, line 20
Label TLV variable See below Label TLV variable See below
The encodings for Label TLVs are found in Section "Label TLVs". The encodings for Label TLVs are found in Section "Label TLVs".
Label Label
If present, the label being released (see procedures below). If present, the label being released (see procedures below).
3.5.11.1. Label Release Message Procedures 3.5.11.1. Label Release Message Procedures
An LSR transmits a Label Release message to a peer when it is no An LSR transmits a Label Release message to a peer when it no longer
longer needs a label previously received from or requested of that needs a label previously received from or requested of that peer.
peer.
An LSR MUST transmit a Label Release message under any of the follow- An LSR MUST transmit a Label Release message under any of the
ing conditions: following conditions:
1. The LSR which sent the label mapping is no longer the next hop 1. The LSR that sent the label mapping is no longer the next hop
for the mapped FEC, and the LSR is configured for conservative for the mapped FEC, and the LSR is configured for conservative
operation. operation.
2. The LSR receives a label mapping from an LSR which is not the 2. The LSR receives a label mapping from an LSR that is not the
next hop for the FEC, and the LSR is configured for conserva- next hop for the FEC, and the LSR is configured for
tive operation. conservative operation.
3. The LSR receives a Label Withdraw message. 3. The LSR receives a Label Withdraw message.
Note that if an LSR is configured for "liberal mode", a release mes- Note that if an LSR is configured for "liberal mode", a release
sage will never be transmitted in the case of conditions (1) and (2) message will never be transmitted in the case of conditions (1) and
as specified above. In this case, the upstream LSR keeps each unused (2) as specified above. In this case, the upstream LSR keeps each
label, so that it can immediately be used later if the downstream unused label, so that it can immediately be used later if the
peer becomes the next hop for the FEC. downstream peer becomes the next hop for the FEC.
The FEC TLV specifies the FEC for which labels are to be released. The FEC TLV specifies the FEC for which labels are to be released.
If no Label TLV follows the FEC, all labels associated with the FEC If no Label TLV follows the FEC, all labels associated with the FEC
are to be released; otherwise only the label specified in the are to be released; otherwise, only the label specified in the
optional Label TLV is to be released. optional Label TLV is to be released.
The FEC TLV may contain the Wildcard FEC Element; if so, it may con- The FEC TLV may contain the Wildcard FEC Element; if so, it may
tain no other FEC Elements. In this case, if the Label Release mes- contain no other FEC Elements. In this case, if the Label Release
sage contains an optional Label TLV, then the label is to be released message contains an optional Label TLV, then the label is to be
for all FECs to which it is bound. If there is not an released for all FECs to which it is bound. If there is not an
optional Label TLV in the Label Release message, then the sending LSR optional Label TLV in the Label Release message, then the sending LSR
is releasing all label mappings previously learned from the receiving is releasing all label mappings previously learned from the receiving
LSR. LSR.
See Appendix A "LDP Label Distribution Procedures" for more details. See Appendix A, "LDP Label Distribution Procedures", for more
details.
3.6. Messages and TLVs for Extensibility 3.6. Messages and TLVs for Extensibility
Support for LDP extensibility includes the rules for the U and F bits Support for LDP extensibility includes the rules for the U- and F-
that specify how an LSR handles unknown TLVs and messages. bits that specify how an LSR handles unknown TLVs and messages.
This section specifies TLVs and messages for vendor-private and This section specifies TLVs and messages for vendor-private and
experimental use. experimental use.
3.6.1. LDP Vendor-private Extensions 3.6.1. LDP Vendor-Private Extensions
Vendor-private TLVs and messages are used to convey vendor-private Vendor-private TLVs and messages are used to convey vendor-private
information between LSRs. information between LSRs.
3.6.1.1. LDP Vendor-private TLVs 3.6.1.1. LDP Vendor-Private TLVs
The Type range 0x3E00 through 0x3EFF is reserved for vendor-private The Type range 0x3E00 through 0x3EFF is reserved for vendor-private
TLVs. TLVs.
The encoding for a vendor-private TLV is: The encoding for a vendor-private TLV is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type (0x3E00-0x3EFF) | Length | |U|F| Type (0x3E00-0x3EFF) | Length |
skipping to change at page 81, line 22 skipping to change at page 78, line 45
| Vendor ID | | Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Data.... | | Data.... |
~ ~ ~ ~
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit U-bit
Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear
(=0), a notification MUST be returned to the message originator (=0), a notification MUST be returned to the message originator
and the entire message MUST be ignored; if U is set (=1), the and the entire message MUST be ignored; if U is set (=1), the
unknown TLV is silently ignored and the rest of the message is unknown TLV is silently ignored and the rest of the message is
processed as if the unknown TLV did not exist. processed as if the unknown TLV did not exist.
The determination as to whether a vendor-private message is under- The determination as to whether a vendor-private message is
stood is based on the Type and the mandatory Vendor ID field. understood is based on the Type and the mandatory Vendor ID field.
Implementations that support vendor-private TLVs MUST support a Implementations that support vendor-private TLVs MUST support a
user-accessible configuration interface that causes the U-bit to user-accessible configuration interface that causes the U-bit to
be set on all transmitted vendor-private TLVs; this requirement be set on all transmitted vendor-private TLVs; this requirement
MAY be satisfied by a user-accessible configuration interface that MAY be satisfied by a user-accessible configuration interface that
prevents transmission of all vendor-private TLVs for which the U- prevents transmission of all vendor-private TLVs for which the U-
bit is clear. bit is clear.
F bit F-bit
Forward unknown TLV bit. This bit only applies when the U bit is Forward unknown TLV bit. This bit only applies when the U-bit is
set and the LDP message containing the unknown TLV is is to be set and the LDP message containing the unknown TLV is to be
forwarded. If F is clear (=0), the unknown TLV is not forwarded forwarded. If F is clear (=0), the unknown TLV is not forwarded
with the containing message; if F is set (=1), the unknown TLV is with the containing message; if F is set (=1), the unknown TLV is
forwarded with the containing message. forwarded with the containing message.
Type Type
Type value in the range 0x3E00 through 0x3EFF. Together, the Type Type value in the range 0x3E00 through 0x3EFF. Together, the Type
and Vendor Id field specify how the Data field is to be inter- and Vendor ID field specify how the Data field is to be
preted. interpreted.
Length Length
Specifies the cumulative length in octets of the Vendor ID and Specifies the cumulative length in octets of the Vendor ID and
Data fields. Data fields.
Vendor Id Vendor ID
802 Vendor ID as assigned by the IEEE. 802 Vendor ID as assigned by the IEEE.
Data Data
The remaining octets after the Vendor ID in the Value field are The remaining octets after the Vendor ID in the Value field are
optional vendor-dependent data. optional vendor-dependent data.
3.6.1.2. LDP Vendor-private Messages 3.6.1.2. LDP Vendor-Private Messages
The Message Type range 0x3E00 through 0x3EFF is reserved for vendor- The Message Type range 0x3E00 through 0x3EFF is reserved for Vendor-
private Messages. Private messages.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Msg Type (0x3E00-0x3EFF) | Message Length | |U| Msg Type (0x3E00-0x3EFF) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor ID | | Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 82, line 39 skipping to change at page 80, line 31
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| Optional Parameters | | Optional Parameters |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit U-bit
Unknown message bit. Upon receipt of an unknown message, if U is Unknown message bit. Upon receipt of an unknown message, if U is
clear (=0), a notification is returned to the message originator; clear (=0), a notification is returned to the message originator;
if U is set (=1), the unknown message is silently ignored. if U is set (=1), the unknown message is silently ignored.
The determination as to whether a vendor-private message is under- The determination as to whether a Vendor-Private message is
stood is based on the Msg Type and the Vendor ID parameter. understood is based on the Msg Type and the Vendor ID parameter.
Implementations that support vendor-private messages MUST support Implementations that support Vendor-Private messages MUST support
a user-accessible configuration interface that causes the U-bit to a user-accessible configuration interface that causes the U-bit to
be set on all transmitted vendor-private messages; this require- be set on all transmitted Vendor-Private messages; this
ment MAY be satisfied by a user-accessible configuration interface requirement MAY be satisfied by a user-accessible configuration
that prevents transmission of all vendor-private messages for interface that prevents transmission of all Vendor-Private
which the U-bit is clear. messages for which the U-bit is clear.
Msg Type Msg Type
Message type value in the range 0x3E00 through 0x3EFF. Together, Message Type value in the range 0x3E00 through 0x3EFF. Together,
the Msg Type and the Vendor ID specify how the message is to be the Msg Type and the Vendor ID specify how the message is to be
interpreted. interpreted.
Message Length Message Length
Specifies the cumulative length in octets of the Message ID, Ven- Specifies the cumulative length in octets of the Message ID,
dor ID, Remaining Mandatory Parameters and Optional Parameters. Vendor ID, Remaining Mandatory Parameters, and Optional
Parameters.
Message ID Message ID
32-bit integer used to identify this message. Used by the sending 32-bit integer used to identify this message. Used by the sending
LSR to facilitate identifying notification messages that may apply LSR to facilitate identifying Notification messages that may apply
to this message. An LSR sending a notification message in to this message. An LSR sending a Notification message in
response to this message will include this Message Id in the noti- response to this message will include this Message ID in the
fication message; see Section "Notification Message". notification message; see Section "Notification Message".
Vendor ID Vendor ID
802 Vendor ID as assigned by the IEEE. 802 Vendor ID as assigned by the IEEE.
Remaining Mandatory Parameters Remaining Mandatory Parameters
Variable length set of remaining required message parameters. Variable length set of remaining required message parameters.
Optional Parameters Optional Parameters
Variable length set of optional message parameters. Variable length set of optional message parameters.
3.6.2. LDP Experimental Extensions 3.6.2. LDP Experimental Extensions
LDP support for experimentation is similar to support for vendor- LDP support for experimentation is similar to support for vendor-
private extensions with the following differences: private extensions with the following differences:
- The Type range 0x3F00 through 0x3FFF is reserved for experimen- - The Type range 0x3F00 through 0x3FFF is reserved for
tal TLVs. experimental TLVs.
- The Message Type range 0x3F00 through 0x3FFF is reserved for - The Message Type range 0x3F00 through 0x3FFF is reserved for
experimental messages. experimental messages.
- The encodings for experimental TLVs and messages are similar to - The encodings for experimental TLVs and messages are similar to
the vendor-private encodings with the following difference. the vendor-private encodings with the following difference.
Experimental TLVs and messages use an Experiment ID field in Experimental TLVs and messages use an Experiment ID field in
place of a Vendor ID field. The Experiment ID field is used place of a Vendor ID field. The Experiment ID field is used
with the Type or Message Type field to specify the interpreta- with the Type or Message Type field to specify the
tion of the experimental TLV or Message. interpretation of the experimental TLV or Message.
Administration of Experiment IDs is the responsibility of the Administration of Experiment IDs is the responsibility of the
experimenters. experimenters.
3.7. Message Summary 3.7. Message Summary
The following are the LDP messages defined in this version of the The following are the LDP messages defined in this version of the
protocol. protocol.
Message Name Type Section Title Message Name Type Section Title
skipping to change at page 84, line 26 skipping to change at page 82, line 18
Hello 0x0100 "Hello Message" Hello 0x0100 "Hello Message"
Initialization 0x0200 "Initialization Message" Initialization 0x0200 "Initialization Message"
KeepAlive 0x0201 "KeepAlive Message" KeepAlive 0x0201 "KeepAlive Message"
Address 0x0300 "Address Message" Address 0x0300 "Address Message"
Address Withdraw 0x0301 "Address Withdraw Message" Address Withdraw 0x0301 "Address Withdraw Message"
Label Mapping 0x0400 "Label Mapping Message" Label Mapping 0x0400 "Label Mapping Message"
Label Request 0x0401 "Label Request Message" Label Request 0x0401 "Label Request Message"
Label Withdraw 0x0402 "Label Withdraw Message" Label Withdraw 0x0402 "Label Withdraw Message"
Label Release 0x0403 "Label Release Message" Label Release 0x0403 "Label Release Message"
Label Abort Request 0x0404 "Label Abort Request Message" Label Abort Request 0x0404 "Label Abort Request Message"
Vendor-Private 0x3E00- "LDP Vendor-private Extensions" Vendor-Private 0x3E00- "LDP Vendor-Private Extensions"
0x3EFF 0x3EFF
Experimental 0x3F00- "LDP Experimental Extensions" Experimental 0x3F00- "LDP Experimental Extensions"
0x3FFF 0x3FFF
3.8. TLV Summary 3.8. TLV Summary
The following are the TLVs defined in this version of the protocol. The following are the TLVs defined in this version of the protocol.
TLV Type Section Title TLV Type Section Title
skipping to change at page 85, line 14 skipping to change at page 83, line 4
Configuration 0x0402 "Hello Message" Configuration 0x0402 "Hello Message"
Sequence Number Sequence Number
IPv6 Transport Address 0x0403 "Hello Message" IPv6 Transport Address 0x0403 "Hello Message"
Common Session 0x0500 "Initialization Message" Common Session 0x0500 "Initialization Message"
Parameters Parameters
ATM Session Parameters 0x0501 "Initialization Message" ATM Session Parameters 0x0501 "Initialization Message"
Frame Relay Session 0x0502 "Initialization Message" Frame Relay Session 0x0502 "Initialization Message"
Parameters Parameters
Label Request 0x0600 "Label Mapping Message" Label Request 0x0600 "Label Mapping Message"
Message ID Message ID
Vendor-Private 0x3E00- "LDP Vendor-private Extensions"
Vendor-Private 0x3E00- "LDP Vendor-Private Extensions"
0x3EFF 0x3EFF
Experimental 0x3F00- "LDP Experimental Extensions" Experimental 0x3F00- "LDP Experimental Extensions"
0x3FFF 0x3FFF
3.9. Status Code Summary 3.9. Status Code Summary
The following are the Status Codes defined in this version of the The following are the Status Codes defined in this version of the
protocol. protocol.
The "E" column is the required setting of the Status Code E-bit; the The "E" column is the required setting of the Status Code E-bit; the
skipping to change at page 85, line 38 skipping to change at page 83, line 29
Status Code E Status Data Section Title Status Code E Status Data Section Title
Success 0 0x00000000 "Status TLV" Success 0 0x00000000 "Status TLV"
Bad LDP Identifier 1 0x00000001 "Events Signaled by ..." Bad LDP Identifier 1 0x00000001 "Events Signaled by ..."
Bad Protocol Version 1 0x00000002 "Events Signaled by ..." Bad Protocol Version 1 0x00000002 "Events Signaled by ..."
Bad PDU Length 1 0x00000003 "Events Signaled by ..." Bad PDU Length 1 0x00000003 "Events Signaled by ..."
Unknown Message Type 0 0x00000004 "Events Signaled by ..." Unknown Message Type 0 0x00000004 "Events Signaled by ..."
Bad Message Length 1 0x00000005 "Events Signaled by ..." Bad Message Length 1 0x00000005 "Events Signaled by ..."
Unknown TLV 0 0x00000006 "Events Signaled by ..." Unknown TLV 0 0x00000006 "Events Signaled by ..."
Bad TLV length 1 0x00000007 "Events Signaled by ..." Bad TLV Length 1 0x00000007 "Events Signaled by ..."
Malformed TLV Value 1 0x00000008 "Events Signaled by ..." Malformed TLV Value 1 0x00000008 "Events Signaled by ..."
Hold Timer Expired 1 0x00000009 "Events Signaled by ..." Hold Timer Expired 1 0x00000009 "Events Signaled by ..."
Shutdown 1 0x0000000A "Events Signaled by ..." Shutdown 1 0x0000000A "Events Signaled by ..."
Loop Detected 0 0x0000000B "Loop Detection" Loop Detected 0 0x0000000B "Loop Detection"
Unknown FEC 0 0x0000000C "FEC Procedures" Unknown FEC 0 0x0000000C "FEC Procedures"
No Route 0 0x0000000D "Label Request Mess ..." No Route 0 0x0000000D "Label Request Mess ..."
No Label Resources 0 0x0000000E "Label Request Mess ..." No Label Resources 0 0x0000000E "Label Request Mess ..."
Label Resources / 0 0x0000000F "Label Request Mess ..." Label Resources / 0 0x0000000F "Label Request Mess ..."
Available Available
Session Rejected/ 1 0x00000010 "Session Initialization" Session Rejected/ 1 0x00000010 "Session Initialization"
No Hello No Hello
Session Rejected/ 1 0x00000011 "Session Initialization" Session Rejected/ 1 0x00000011 "Session Initialization"
Parameters Advertisement Mode Parameters Advertisement Mode
Session Rejected/ 1 0x00000012 "Session Initialization" Session Rejected/ 1 0x00000012 "Session Initialization"
Parameters Max PDU Length Parameters Max PDU Length
Session Rejected/ 1 0x00000013 "Session Initialization" Session Rejected/ 1 0x00000013 "Session Initialization"
Parameters Label Range Parameters Label Range
KeepAlive Timer 1 0x00000014 "Events Signaled by ..." KeepAlive Timer 1 0x00000014 "Events Signaled by ..."
Expired Expired
Label Request Aborted 0 0x00000015 "Label Request Abort ..." Label Request Aborted 0 0x00000015 "Label Abort Request ..."
Missing Message 0 0x00000016 "Events Signaled by ..." Missing Message 0 0x00000016 "Events Signaled by ..."
Parameters Parameters
Unsupported Address 0 0x00000017 "FEC Procedures" Unsupported Address 0 0x00000017 "FEC Procedures"
Family "Address Message Proc ..." Family "Address Message Proc ..."
Session Rejected/ 1 0x00000018 "Session Initialization" Session Rejected/ 1 0x00000018 "Session Initialization"
Bad KeepAlive Time Bad KeepAlive Time
Internal Error 1 0x00000019 "Events Signaled by ..." Internal Error 1 0x00000019 "Events Signaled by ..."
3.10. Well-known Numbers 3.10. Well-Known Numbers
3.10.1. UDP and TCP Ports 3.10.1. UDP and TCP Ports
The UDP port for LDP Hello messages is 646. The UDP port for LDP Hello messages is 646.
The TCP port for establishing LDP session connections is 646. The TCP port for establishing LDP session connections is 646.
3.10.2. Implicit NULL Label 3.10.2. Implicit NULL Label
The Implicit NULL label is defined in [RFC3031] as follows: The Implicit NULL label is defined in [RFC3031] as follows:
skipping to change at page 87, line 7 skipping to change at page 84, line 36
next to Rd, but that Rd has distributed a binding of Implicit NULL to next to Rd, but that Rd has distributed a binding of Implicit NULL to
the corresponding address prefix, then instead of replacing the value the corresponding address prefix, then instead of replacing the value
of the label on top of the label stack, Ru pops the label stack, and of the label on top of the label stack, Ru pops the label stack, and
then forwards the resulting packet to Rd." then forwards the resulting packet to Rd."
The implicit NULL label is represented in LDP as a Generic Label TLV The implicit NULL label is represented in LDP as a Generic Label TLV
with a Label field value of 3, as defined in [RFC3032]. with a Label field value of 3, as defined in [RFC3032].
4. IANA Considerations 4. IANA Considerations
LDP defines the following name spaces which require management: LDP defines the following name spaces that require management:
- Message Type Name Space. - Message Type Name Space
- TLV Type Name Space. - TLV Type Name Space
- FEC Type Name Space. - FEC Type Name Space
- Status Code Name Space. - Status Code Name Space
- Experiment ID Name Space. - Experiment ID Name Space
The following sections provide guidelines for managing these name The following sections provide guidelines for managing these name
spaces. spaces.
4.1. Message Type Name Space 4.1. Message Type Name Space
LDP divides the name space for message types into three ranges. The LDP divides the name space for message types into three ranges. The
following are the guidelines for managing these ranges: following are the guidelines for managing these ranges:
- Message Types 0x0000 - 0x3DFF. Message types in this range are - Message Types 0x0000 - 0x3DFF. Message types in this range are
part of the LDP base protocol. Following the policies outlined part of the LDP base protocol. Following the policies outlined
in [IANA], Message types in this range are allocated through an in [IANA], Message types in this range are allocated through an
IETF Consensus action. IETF Consensus action.
- Message Types 0x3E00 - 0x3EFF. Message types in this range are - Message Types 0x3E00 - 0x3EFF. Message types in this range are
reserved for Vendor Private extensions and are the responsibil- reserved for Vendor-Private extensions and are the
ity of the individual vendors (see Section "LDP Vendor-private responsibility of the individual vendors (see Section "LDP
Messages"). IANA management of this range of the Message Type Vendor-Private Messages"). IANA management of this range of
Name Space is unnecessary. the Message Type Name Space is unnecessary.
- Message Types 0x3F00 - 0x3FFF. Message types in this range are - Message Types 0x3F00 - 0x3FFF. Message types in this range are
reserved for Experimental extensions and are the responsibility reserved for Experimental extensions and are the responsibility
of the individual experimenters (see Sections "LDP Experimental of the individual experimenters (see Sections "LDP Experimental
Extensions" and "Experiment ID Name Space"). IANA management Extensions" and "Experiment ID Name Space"). IANA management
of this range of the Message Type Name Space is unnecessary; of this range of the Message Type Name Space is unnecessary;
however, IANA is responsible for managing part of the Experi- however, IANA is responsible for managing part of the
ment ID Name Space (see below). Experiment ID Name Space (see below).
4.2. TLV Type Name Space 4.2. TLV Type Name Space
LDP divides the name space for TLV types into three ranges. The fol- LDP divides the name space for TLV types into three ranges. The
lowing are the guidelines for managing these ranges: following are the guidelines for managing these ranges:
- TLV Types 0x0000 - 0x3DFF. TLV types in this range are part of - TLV Types 0x0000 - 0x3DFF. TLV types in this range are part of
the LDP base protocol. Following the policies outlined in the LDP base protocol. Following the policies outlined in
[IANA], TLV types in this range are allocated through an IETF [IANA], TLV types in this range are allocated through an IETF
Consensus action. Consensus action.
- TLV Types 0x3E00 - 0x3EFF. TLV types in this range are - TLV Types 0x3E00 - 0x3EFF. TLV types in this range are
reserved for Vendor Private extensions and are the responsibil- reserved for Vendor-Private extensions and are the
ity of the individual vendors (see Section "LDP Vendor-private responsibility of the individual vendors (see Section "LDP
TLVs"). IANA management of this range of the TLV Type Name Vendor-Private TLVs"). IANA management of this range of the
Space is unnecessary. TLV Type Name Space is unnecessary.
- TLV Types 0x3F00 - 0x3FFF. TLV types in this range are - TLV Types 0x3F00 - 0x3FFF. TLV types in this range are
reserved for Experimental extensions and are the responsibility reserved for Experimental extensions and are the responsibility
of the individual experimenters (see Sections "LDP Experimental of the individual experimenters (see Sections "LDP Experimental
Extensions" and "Experiment ID Name Space"). IANA management Extensions" and "Experiment ID Name Space"). IANA management
of this range of the TLV Name Space is unnecessary; however, of this range of the TLV Name Space is unnecessary; however,
IANA is responsible for managing part of the Experiment ID Name IANA is responsible for managing part of the Experiment ID Name
Space (see below). Space (see below).
4.3. FEC Type Name Space 4.3. FEC Type Name Space
skipping to change at page 88, line 40 skipping to change at page 86, line 22
The range for Status Codes is 0x00000000 - 0x3FFFFFFF. The range for Status Codes is 0x00000000 - 0x3FFFFFFF.
Following the policies outlined in [IANA], Status Codes in the range Following the policies outlined in [IANA], Status Codes in the range
0x00000000 - 0x1FFFFFFF are allocated through an IETF Consensus 0x00000000 - 0x1FFFFFFF are allocated through an IETF Consensus
action, codes in the range 0x20000000 - 0x3EFFFFFF are allocated as action, codes in the range 0x20000000 - 0x3EFFFFFF are allocated as
First Come First Served, and codes in the range 0x3F000000 - First Come First Served, and codes in the range 0x3F000000 -
0x3FFFFFFF are reserved for Private Use. 0x3FFFFFFF are reserved for Private Use.
4.5. Experiment ID Name Space 4.5. Experiment ID Name Space
The range for Experiment Ids is 0x00000000 - 0xffffffff. The range for Experiment IDs is 0x00000000 - 0xffffffff.
Following the policies outlined in [IANA], Experiment Ids in the Following the policies outlined in [IANA], Experiment IDs in the
range 0x00000000 - 0xefffffff are allocated as First Come First range 0x00000000 - 0xefffffff are allocated as First Come First
Served and Experiment Ids in the range 0xf0000000 - 0xffffffff are Served and Experiment IDs in the range 0xf0000000 - 0xffffffff are
reserved for Private Use. reserved for Private Use.
5. Security Considerations 5. Security Considerations
This section identifies threats to which LDP may be vulnerable and This section identifies threats to which LDP may be vulnerable and
discusses means by which those threats might be mitigated. discusses means by which those threats might be mitigated.
5.1. Spoofing 5.1. Spoofing
There are two types of LDP communication that could be the target of There are two types of LDP communication that could be the target of
a spoofing attack. a spoofing attack.
1. Discovery exchanges carried by UDP. 1. Discovery exchanges carried by UDP
LSRs indicate their willingness to establish and maintain LDP ses- LSRs indicate their willingness to establish and maintain LDP
sions by periodically sending Hello messages. Receipt of a Hello sessions by periodically sending Hello messages. Receipt of a
serves to create a new "Hello adjacency", if one does not already Hello serves to create a new "Hello adjacency", if one does not
exist, or to refresh an existing one. Spoofing a Hello packet for already exist, or to refresh an existing one. Spoofing a Hello
an existing adjacency can cause the adjacency to time out and that packet for an existing adjacency can cause the adjacency to time
can result in termination of the associated session. This can out and that can result in termination of the associated session.
occur when the spoofed Hello specifies a small Hold Time, causing This can occur when the spoofed Hello specifies a small Hold Time,
the receiver to expect Hellos within this interval, while the true causing the receiver to expect Hellos within this interval, while
neighbor continues sending Hellos at the lower, previously agreed the true neighbor continues sending Hellos at the lower,
to, frequency. previously agreed to, frequency.
LSRs directly connected at the link level exchange Basic Hello LSRs directly connected at the link level exchange Basic Hello
messages over the link. The threat of spoofed Basic Hellos can be messages over the link. The threat of spoofed Basic Hellos can be
reduced by: reduced by:
o Accepting Basic Hellos only on interfaces to which LSRs that o Accepting Basic Hellos only on interfaces to which LSRs that
can be trusted are directly connected. can be trusted are directly connected.
o Ignoring Basic Hellos not addressed to the All Routers on o Ignoring Basic Hellos not addressed to the All Routers on
this Subnet multicast group. this Subnet multicast group.
LSRs not directly connected at the link level may use Extended LSRs not directly connected at the link level may use Extended
Hello messages to indicate willingness to establish an LDP ses- Hello messages to indicate willingness to establish an LDP
sion. An LSR can reduce the threat of spoofed Extended Hellos by session. An LSR can reduce the threat of spoofed Extended Hellos
filtering them and accepting only those originating at sources by filtering them and accepting only those originating at sources
permitted by an access list. permitted by an access list.
2. Session communication carried by TCP. 2. Session communication carried by TCP
LDP specifies use of the TCP MD5 Signature Option to provide for LDP specifies use of the TCP MD5 Signature Option to provide for
the authenticity and integrity of session messages. the authenticity and integrity of session messages.
[RFC2385] asserts that MD5 authentication is now considered by [RFC2385] asserts that MD5 authentication is now considered by
some to be too weak for this application. It also points out that some to be too weak for this application. It also points out that
a similar TCP option with a stronger hashing algorithm (it cites a similar TCP option with a stronger hashing algorithm (it cites
SHA-1 as an example) could be deployed. To our knowledge no such SHA-1 as an example) could be deployed. To our knowledge, no such
TCP option has been defined and deployed. However, we note that TCP option has been defined and deployed. However, we note that
LDP can use whatever TCP message digest techniques are available, LDP can use whatever TCP message digest techniques are available,
and when one stronger than MD5 is specified and implemented, and when one stronger than MD5 is specified and implemented,
upgrading LDP to use it would be relatively straightforward. upgrading LDP to use it would be relatively straightforward.
5.2. Privacy 5.2. Privacy
LDP provides no mechanism for protecting the privacy of label distri- LDP provides no mechanism for protecting the privacy of label
bution. distribution.
The security requirements of label distribution protocols are essen- The security requirements of label distribution protocols are
tially identical to those of the protocols which distribute routing essentially identical to those of the protocols that distribute
information. By providing a mechanism to ensure the authenticity and routing information. By providing a mechanism to ensure the
integrity of its messages LDP provides a level of security which is authenticity and integrity of its messages, LDP provides a level of
at least as good as, though no better than, that which can be pro- security that is at least as good as, though no better than, that
vided by the routing protocols themselves. The more general issue of which can be provided by the routing protocols themselves. The more
whether privacy should be required for routing protocols is beyond general issue of whether privacy should be required for routing
the scope of this document. protocols is beyond the scope of this document.
One might argue that label distribution requires privacy to address One might argue that label distribution requires privacy to address
the threat of label spoofing. However, that privacy would not pro- the threat of label spoofing. However, that privacy would not
tect against label spoofing attacks since data packets carry labels protect against label spoofing attacks since data packets carry
in the clear. Furthermore, label spoofing attacks can be made with- labels in the clear. Furthermore, label spoofing attacks can be made
out knowledge of the FEC bound to a label. without knowledge of the FEC bound to a label.
To avoid label spoofing attacks, it is necessary to ensure that To avoid label spoofing attacks, it is necessary to ensure that
labeled data packets are labeled by trusted LSRs and that the labels labeled data packets are labeled by trusted LSRs and that the labels
placed on the packets are properly learned by the labeling LSRs. placed on the packets are properly learned by the labeling LSRs.
5.3. Denial of Service 5.3. Denial of Service
LDP provides two potential targets for denial of service (DoS) LDP provides two potential targets for Denial of Service (DoS)
attacks: attacks:
1. Well known UDP Port for LDP Discovery 1. Well-known UDP Port for LDP Discovery
An LSR administrator can address the threat of DoS attacks via An LSR administrator can address the threat of DoS attacks via
Basic Hellos by ensuring that the LSR is directly connected only Basic Hellos by ensuring that the LSR is directly connected only
to peers which can be trusted to not initiate such an attack. to peers that can be trusted to not initiate such an attack.
Interfaces to peers interior to the administrator's domain should Interfaces to peers interior to the administrator's domain should
not represent a threat since interior peers are under the adminis- not represent a threat since interior peers are under the
trator's control. Interfaces to peers exterior to the domain rep- administrator's control. Interfaces to peers exterior to the
resent a potential threat since exterior peers are not. An admin- domain represent a potential threat since exterior peers are not.
istrator can reduce that threat by connecting the LSR only to An administrator can reduce that threat by connecting the LSR only
exterior peers that can be trusted to not initiate a Basic Hello to exterior peers that can be trusted to not initiate a Basic
attack. Hello attack.
DoS attacks via Extended Hellos are potentially a more serious DoS attacks via Extended Hellos are potentially a more serious
threat. This threat can be addressed by filtering Extended Hellos threat. This threat can be addressed by filtering Extended Hellos
using access lists that define addresses with which extended dis- using access lists that define addresses with which Extended
covery is permitted. However, performing the filtering requires Discovery is permitted. However, performing the filtering
LSR resource. requires LSR resource.
In an environment where a trusted MPLS cloud can be identified, In an environment where a trusted MPLS cloud can be identified,
LSRs at the edge of the cloud can be used to protect interior LSRs LSRs at the edge of the cloud can be used to protect interior LSRs
against DoS attacks via Extended Hellos by filtering out Extended against DoS attacks via Extended Hellos by filtering out Extended
Hellos originating outside of the trusted MPLS cloud, accepting Hellos originating outside of the trusted MPLS cloud, accepting
only those originating at addresses permitted by access lists. only those originating at addresses permitted by access lists.
This filtering protects LSRs in the interior of the cloud but con- This filtering protects LSRs in the interior of the cloud but
sumes resources at the edges. consumes resources at the edges.
2. Well known TCP port for LDP Session Establishment 2. Well-known TCP port for LDP Session Establishment
Like other control plane protocols that use TCP, LDP may be the Like other control plane protocols that use TCP, LDP may be the
target of DoS attacks, such a SYN attacks. LDP is no more or less target of DoS attacks, such as SYN attacks. LDP is no more or
vulnerable to such attacks than other control plane protocols that less vulnerable to such attacks than other control plane protocols
use TCP. that use TCP.
The threat of such attacks can be mitigated somewhat by the fol- The threat of such attacks can be mitigated somewhat by the
lowing: following:
o An LSR SHOULD avoid promiscuous TCP listens for LDP session o An LSR SHOULD avoid promiscuous TCP listens for LDP session
establishment. It SHOULD use only listens that are specific establishment. It SHOULD use only listens that are specific
to discovered peers. This enables it to drop attack packets to discovered peers. This enables it to drop attack packets
early in their processing since they are less likely to early in their processing since they are less likely to
match existing or in-progress connections. match existing or in-progress connections.
o The use of the MD5 option helps somewhat since it prevents a o The use of the MD5 option helps somewhat since it prevents a
SYN from being accepted unless the MD5 segment checksum is SYN from being accepted unless the MD5 segment checksum is
valid. However, the receiver must compute the checksum valid. However, the receiver must compute the checksum
before it can decide to discard an otherwise acceptable SYN before it can decide to discard an otherwise acceptable SYN
segment. segment.
o The use of access list mechanisms applied at the boundary of o The use of access list mechanisms applied at the boundary of
the MPLS cloud in a manner similar to that suggested above the MPLS cloud in a manner similar to that suggested above
for Extended Hellos can protect the interior against attacks for Extended Hellos can protect the interior against attacks
originating from outside the cloud. originating from outside the cloud.
6. Areas for Future Study 6. Areas for Future Study
The following topics not addressed in this version of LDP are possi- The following topics not addressed in this version of LDP are
ble areas for future study: possible areas for future study:
- Section 2.16 of the MPLS architecture [RFC3031] requires that - Section 2.16 of the MPLS architecture [RFC3031] requires that
the initial label distribution protocol negotiation between the initial label distribution protocol negotiation between
peer LSRs enable each LSR to determine whether its peer is peer LSRs enable each LSR to determine whether its peer is
capable of popping the label stack. This version of LDP capable of popping the label stack. This version of LDP
assumes that LSRs support label popping for all link types assumes that LSRs support label popping for all link types
except ATM and Frame Relay. A future version may specify means except ATM and Frame Relay. A future version may specify means
to make this determination part of the session initiation nego- to make this determination part of the session initiation
tiation. negotiation.
- LDP support for CoS (class of service) is not specified in this - LDP support for CoS (Class of Service) is not specified in this
version. CoS support may be addressed in a future version. version. CoS support may be addressed in a future version.
- LDP support for multicast is not specified in this version. - LDP support for multicast is not specified in this version.
Multicast support may be addressed in a future version. Multicast support may be addressed in a future version.
- LDP support for multipath label switching is not specified in - LDP support for multipath label switching is not specified in
this version. Multipath support may be addressed in a future this version. Multipath support may be addressed in a future
version. version.
- LDP support for signalling the maximum transmission unit is not - LDP support for signaling the maximum transmission unit is not
specified in this version. It is discussed in the experimental specified in this version. It is discussed in the experimental
document [LDP-MTU]. document [LDP-MTU].
- The current specification does not address basic peer discovery - The current specification does not address basic peer discovery
on non-broadcast multi access (NBMA) media. The solution avail- on Non-Broadcast Multi-Access (NBMA) media. The solution
able in the current specification is to use extended peer dis- available in the current specification is to use extended peer
covery in such setups. The issue of defining a mechanism seman- discovery in such setups. The issue of defining a mechanism
tically similar to basic discovery (1 hop limit, bind the hello semantically similar to Basic Discovery (1 hop limit, bind the
adjacency to an interface) that uses a preconfigured neighbor hello adjacency to an interface) that uses preconfigured
addresses, is left for further study. neighbor addresses is left for further study.
- The current specification does not support shutting down an - The current specification does not support shutting down an
adjacency. The motivation for doing it, and the mechanisms for adjacency. The motivation for doing it and the mechanisms for
achieving it are left for further study. achieving it are left for further study.
- The current specification does not include a method for secur- - The current specification does not include a method for
ing Hello messages, to detect spoofing of Hellos. The scenarios securing Hello messages, to detect spoofing of Hellos. The
where this is necessary, as well as the mechanism for achieving scenarios where this is necessary, as well as the mechanism for
it are left for future study. achieving it are left for future study.
- The current specification does not have the ability to detect a - The current specification does not have the ability to detect a
stateless fast control plane restart. The method for achieving stateless fast control plane restart. The method for achieving
this, possibly through an "incarnation/instance" number carried this, possibly through an "incarnation/instance" number carried
in the Hello message is left for future study. in the Hello message, is left for future study.
- The current specification does not support an "end of LIB" mes- - The current specification does not support an "end of LIB"
sage, analogous to BGP's end of RIB message which an LDP LSR message, analogous to BGP's "end of RIB" message that an LDP
(operating in DU mode) would use following session establish- LSR (operating in DU mode) would use following session
ment. The discussion on the need for such a mechanism and its establishment. The discussion on the need for such a mechanism
implementation are left for future study. and its implementation is left for future study.
- The current specification does not deal with situations where - The current specification does not deal with situations where
different LSRs advertise the same address. Such situations different LSRs advertise the same address. Such situations
typically occur as the result of configuration errors, and the typically occur as the result of configuration errors, and the
goal in this case is to provide the LSRs advertising the same goal in this case is to provide the LSRs advertising the same
address with enough information to enable operators to take address with enough information to enable operators to take
corrective action. The specification of this mechanism is left corrective action. The specification of this mechanism is left
for a separate document. for a separate document.
7. Changes from RFC3036 7. Changes from RFC3036
skipping to change at page 93, line 23 skipping to change at page 90, line 40
different LSRs advertise the same address. Such situations different LSRs advertise the same address. Such situations
typically occur as the result of configuration errors, and the typically occur as the result of configuration errors, and the
goal in this case is to provide the LSRs advertising the same goal in this case is to provide the LSRs advertising the same
address with enough information to enable operators to take address with enough information to enable operators to take
corrective action. The specification of this mechanism is left corrective action. The specification of this mechanism is left
for a separate document. for a separate document.
7. Changes from RFC3036 7. Changes from RFC3036
Here is a list of changes from RFC3036 Here is a list of changes from RFC3036
1. Removed the Host Address FEC and references to it, since it is 1. Removed the Host Address FEC and references to it, since it is
not used by any implementation. not used by any implementation.
2. Split the reference list into normative and non-normative ref-
erences 2. Split the reference list into normative and informative
3. Removed "MPLS using ATM VP Switching" from the list of norma- references
tive references, and references to it.
3. Removed "MPLS using ATM VP Switching" from the list of
normative references, and references to it.
4. Removed reference to RFC 1700 and replaced it with a link to 4. Removed reference to RFC 1700 and replaced it with a link to
http://www.iana.org/assignments/address-family-numbers. http://www.iana.org/assignments/address-family-numbers.
5. Removed reference to RFC 1771 and replaced it with a reference 5. Removed reference to RFC 1771 and replaced it with a reference
to RFC 4271. to RFC 4271.
6. Clarified the use of the F bit.
7. Added option to allow split horizon when doing ordered control. 6. Clarified the use of the F-bit.
7. Added option to allow split horizon when doing Ordered
Control.
8. Clarified the processing of messages with the U-bit set during 8. Clarified the processing of messages with the U-bit set during
the session initialization procedures the session initialization procedures
9. Clarified the processing of the E-bit during session initial-
ization procedures. 9. Clarified the processing of the E-bit during session
10. Added text explaining that the shutdown message in the state initialization procedures.
transition diagram is implemented as as a notification message
with a status TLV indicating a fatal error. 10. Added text explaining that the Shutdown message in the state
transition diagram is implemented as a notification message
with a Status TLV indicating a fatal error.
11. Added case for TLV length too short in the specification for 11. Added case for TLV length too short in the specification for
handling malformed TLVs. handling malformed TLVs.
12. Explained the security threat posed by hello spoofing. 12. Explained the security threat posed by hello spoofing.
13. Added reference to 4271 and 4278 and text for standards matu-
rity variance with regards to the MD5 option. 13. Added reference to 4271 and 4278 and text for standards
maturity variance with regards to the MD5 option.
14. Added text from 3031 explaining the handling of implicit NULL 14. Added text from 3031 explaining the handling of implicit NULL
label. label.
15. Included the encoding of DLCIs to remove normative reference to 15. Included the encoding of DLCIs to remove normative reference
3034. to 3034.
16. Moved references to 3031, 3032 and 3034 to informative.
17. In the section describing handling of unknown TLV, removed ref- 16. Moved references to 3031, 3032, and 3034 to informative.
erence to inexistent section (errata in original document).
17. In the section describing handling of unknown TLV, removed
reference to inexistent section (errata in original document).
18. Added text clarifying how to achieve interoperability when 18. Added text clarifying how to achieve interoperability when
sending vendor-private TLVs and messages. sending vendor-private TLVs and messages.
19. In the "receive label request" procedures, if a loop is 19. In the "receive label request" procedures, if a loop is
detected, changed the procedure to send a notification before detected, changed the procedure to send a notification before
aborting the rest of the processing. aborting the rest of the processing.
20. In "receive label release" procedures, clarified the behavior 20. In "receive label release" procedures, clarified the behavior
for merge-capable LSRs. for merge-capable LSRs.
21. In "receive label release" procedures, clarified the behavior 21. In "receive label release" procedures, clarified the behavior
for receipt of an unknown FEC. for receipt of an unknown FEC.
22. In note 4 of "Detect Change in FEC Next Hop", modified the text
to reference the correct set of conditions for sending a label 22. In note 4 of "Detect Change in FEC Next Hop", modified the
request procedure (typo in the original document). text to reference the correct set of conditions for sending a
label request procedure (typo in the original document).
23. In the procedures for "LSR decides to no longer label switch a 23. In the procedures for "LSR decides to no longer label switch a
FEC", clarified the fact that the label must not be reused FEC", clarified the fact that the label must not be reused
until a label release is received. until a label release is received.
24. In the routine "Prepare_Label_Mapping_Attributes" added a note
regarding the treatment of unknown TLVs according to their U 24. In the routine "Prepare_Label_Mapping_Attributes", added a
and F bits. note regarding the treatment of unknown TLVs according to
25. In the address message processing procedures, clarified the their U and F-bits.
behavior for the case where an LSR receives re-advertisement of
an address previously advertised it, or withdrawal of an 25. In the Address message processing procedures, clarified the
behavior for the case where an LSR receives re-advertisement
of an address previously advertised it, or withdrawal of an
address from an LSR that has not previously advertised that address from an LSR that has not previously advertised that
address. address.
26. In the routine "Receive Label Mapping" clarified the meaning of
PrevAdvLabel when no label advertisement message has been sent 26. In the routine "Receive Label Mapping", clarified the meaning
previously. of PrevAdvLabel when no label advertisement message has been
sent previously.
27. In the "Receive Label Mapping" procedures, if a loop is 27. In the "Receive Label Mapping" procedures, if a loop is
detected, modified the procedure to send a notification before detected, modified the procedure to send a notification before
aborting the rest of the processing. aborting the rest of the processing.
28. In the "Receive Label Mapping" procedures, corrected step 28. In the "Receive Label Mapping" procedures, corrected step
LMp.10 to handle label mapping messages for additional (non- LMp.10 to handle label mapping messages for additional (non-
merged) LSPs for the FEC. merged) LSPs for the FEC.
29. In the "Receive Label Mapping" procedures, clarified behavior 29. In the "Receive Label Mapping" procedures, clarified behavior
when receiving a duplicate label for the same FEC. when receiving a duplicate label for the same FEC.
30. In the routine "Receive Label Abort Request" clarified the
30. In the routine "Receive Label Abort Request", clarified the
behavior for non-merging LSRs. behavior for non-merging LSRs.
31. Added the following items to the section discussing areas for 31. Added the following items to the section discussing areas for
future study: future study:
o extensions for communicating the maximum transmission unit o extensions for communicating the maximum transmission unit
o basic peer discovery on NBMA media o basic peer discovery on NBMA media
o option of shutting down an adjacency o option of shutting down an adjacency
o mechanisms for securing Hello messages o mechanisms for securing Hello messages
o detection of a stateless fast control plane restart o detection of a stateless fast control plane restart
o support of "end of LIB" message o support of "end of LIB" message
o mechanisms for dealing with the case where different LSRs o mechanisms for dealing with the case where different LSRs
advertise the same address. advertise the same address
8. Acknowledgments 8. Acknowledgments
This document was originally published as RFC 3036 in January 2001. This document is produced as part of advancing the LDP specification
It was produced by the MPLS working of the IETF and was jointly to draft standard status. This document was originally published as
authored by Loa Andersson, Paul Doolan, Nancy Feldman, Andre Fredette RFC 3036 in January 2001. It was produced by the MPLS Working Group
and Bob Thomas. of the IETF and was jointly authored by Loa Andersson, Paul Doolan,
Nancy Feldman, Andre Fredette, and Bob Thomas.
The ideas and text in RFC3036 were collected from a number of The ideas and text in RFC3036 were collected from a number of
sources. We would like to thank Rick Boivie, Ross Callon, Alex sources. We would like to thank Rick Boivie, Ross Callon, Alex
Conta, Eric Gray, Yoshihiro Ohba, Eric Rosen, Bernard Suter, Yakov Conta, Eric Gray, Yoshihiro Ohba, Eric Rosen, Bernard Suter, Yakov
Rekhter, and Arun Viswanathan for their input for RFC3036. Rekhter, and Arun Viswanathan for their input for RFC3036.
The editors would like to thank Eric Gray, David Black and Sam Hart- The editors would like to thank Eric Gray, David Black, and Sam
man for their input to and review of the current document. Hartman for their input to and review of the current document.
In addition, the editors would like to thank the members of the mpls In addition, the editors would like to thank the members of the MPLS
working group for their ideas and the support they have given to this Working Group for their ideas and the support they have given to this
document, and in particular to Eric Rosen, Luca Martini, Markus Jork, document, and in particular, to Eric Rosen, Luca Martini, Markus
Mark Duffy, Vach Kompella, Kishore Tiruveedhula. Rama Ramakrishnan, Jork, Mark Duffy, Vach Kompella, Kishore Tiruveedhula, Rama
Nick Weeds, Adrian Farrel and Andy Malis. Ramakrishnan, Nick Weeds, Adrian Farrel, and Andy Malis.
9. References 9. References
9.1. Normative references 9.1. Normative References
[IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC 1321, [IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing
April 1992. an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
[RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM Adap- [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC
tation Layer 5", RFC 1483, July 1993. 1321, April 1992.
[ASSIGNED_AF] http://www.iana.org/assignments/address-family-numbers [ASSIGNED_AF] http://www.iana.org/assignments/address-family-numbers
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP
MD5 Signature Option", RFC 2385, August 1998. MD5 Signature Option", RFC 2385, August 1998.
[RFC3035] Davie, B., Lawrence, J., McCloghrie, K., Rekhter, Y., [RFC3035] Davie, B., Lawrence, J., McCloghrie, K., Rosen, E.,
Rosen, E., Swallow, G. and P. Doolan, "MPLS using LDP and Swallow, G., Rekhter, Y., and P. Doolan, "MPLS using
ATM VC Switching", RFC 3035, January 2001. LDP and ATM VC Switching", RFC 3035, January 2001.
[RFC3037] Thomas, B. and E. Gray, "LDP Applicability", RFC 3037, [RFC3037] Thomas, B. and E. Gray, "LDP Applicability", RFC 3037,
January 2001. January 2001.
9.2. Non-normative references 9.2. Informative References
[CRLDP] L. Andersson, A. Fredette, B. Jamoussi, R. Callon, P.
Doolan, N. Feldman, E. Gray, J. Halpern, J. Heinanen T.
E. Kilty, A. G. Malis, M. Girish, K. Sundell, P. Vaana-
nen, T. Worster, L. Wu, R. Dantu, "Constraint-Based LSP
Setup using LDP", RFC 3212, January 2002
[DIFFSERV] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
and W. Weiss, "An Architecture for Differentiated Ser-
vices", RFC 2475, December 1998.
[LDP-MTU] Black, B. and Kompella, K. "Maximum Transmission Unit
Signalling Extensions for the Label Distribution Proto-
col", draft-ietf-mpls-ldp-mtu-extensions-03.txt, April
2004.
[RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S. and S. [CRLDP] Jamoussi, B., Ed., Andersson, L., Callon, R., Dantu,
R., Wu, L., Doolan, P., Worster, T., Feldman, N.,
Fredette, A., Girish, M., Gray, E., Heinanen, J.,
Kilty, T., and A. Malis, "Constraint-Based LSP Setup
using LDP", RFC 3212, January 2002.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 [LDP-MTU] Black, B. and K. Kompella, "Maximum Transmission Unit
Functional Specification", RFC 2205, September 1997. Signalling Extensions for the Label Distribution
Protocol", RFC 3988, January 2005.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
1998.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J. [RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and
McManus, "Requirements for Traffic Engineering over J. McManus, "Requirements for Traffic Engineering Over
MPLS", RFC 2702, September 1999. MPLS", RFC 2702, September 1999.
[RFC3031] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol [RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
Label Switching Architecture", RFC 3031, January 2001. "Multiprotocol Label Switching Architecture", RFC 3031,
[RFC3032] Rosen, E., Rekhter, Y., Tappan, D., Farinacci, D.,
Fedorkow, G., Li, T. and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
[RFC3034] Conta, A., Doolan, P. and A. Malis, "Use of Label Switch-
ing on Frame Relay Networks Specification", RFC 3034,
January 2001. January 2001.
[RFC4271] Rekhter, Y., Li, T. and Hares, S. "A Border Gateway Pro- [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
tocol 4 (BGP-4)", RFC 4271, January 2006. Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
[RFC4278] Bellovin, S., Zinin, A., "Standards Maturity Variance
Regarding the TCP MD5 Signature Option (RFC 2385) and the
BGP-4 Specification", RFC 4278, January 2006.
10. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any assur-
ances of licenses to be made available, or the result of an attempt
made to obtain a general license or permission for the use of such
proprietary rights by implementers or users of this specification can