draft-ietf-mpls-ldp-11.txt   rfc3036.txt 
Network Working Group Loa Andersson
Internet Draft Nortel Networks Inc.
Expiration Date: February 2001
Paul Doolan
Ennovate Networks
Nancy Feldman Network Working Group L. Andersson
IBM Corp Request for Comments: 3036 Nortel Networks Inc.
Category: Standards Track P. Doolan
Andre Fredette Ennovate Networks
PhotonEx Corp N. Feldman
IBM Corp
Bob Thomas A. Fredette
Cisco Systems, Inc. PhotonEx Corp
B. Thomas
August 2000 Cisco Systems, Inc.
January 2001
LDP Specification LDP Specification
draft-ietf-mpls-ldp-11.txt
Status of this Memo Status of this Memo
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Abstract Abstract
The architecture for Multi Protocol Label Switching (MPLS) is The architecture for Multi Protocol Label Switching (MPLS) is
described in [ARCH]. A fundamental concept in MPLS is that two Label described in RFC 3031. A fundamental concept in MPLS is that two
Switching Routers (LSRs) must agree on the meaning of the labels used Label Switching Routers (LSRs) must agree on the meaning of the
to forward traffic between and through them. This common labels used to forward traffic between and through them. This common
understanding is achieved by using a set of procedures, called a understanding is achieved by using a set of procedures, called 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 [LDPAPPLIC]. paths.
Table of Contents Table of Contents
1 LDP Overview ....................................... 7 1 LDP Overview ....................................... 5
1.1 LDP Peers .......................................... 7 1.1 LDP Peers .......................................... 6
1.2 LDP Message Exchange ............................... 8 1.2 LDP Message Exchange ............................... 6
1.3 LDP Message Structure .............................. 8 1.3 LDP Message Structure .............................. 7
1.4 LDP Error Handling ................................. 9 1.4 LDP Error Handling ................................. 7
1.5 LDP Extensibility and Future Compatibility ......... 9 1.5 LDP Extensibility and Future Compatibility ......... 7
1.6 Specification Language ............................. 9 1.6 Specification Language ............................. 7
2 LDP Operation ...................................... 9 2 LDP Operation ...................................... 8
2.1 FECs ............................................... 9 2.1 FECs ............................................... 8
2.2 Label Spaces, Identifiers, Sessions and Transport .. 11 2.2 Label Spaces, Identifiers, Sessions and Transport .. 9
2.2.1 Label Spaces ....................................... 11 2.2.1 Label Spaces ....................................... 9
2.2.2 LDP Identifiers .................................... 12 2.2.2 LDP Identifiers .................................... 10
2.2.3 LDP Sessions ....................................... 12 2.2.3 LDP Sessions ....................................... 10
2.2.4 LDP Transport ...................................... 12 2.2.4 LDP Transport ...................................... 11
2.3 LDP Sessions between non-Directly Connected LSRs ... 13 2.3 LDP Sessions between non-Directly Connected LSRs ... 11
2.4 LDP Discovery ..................................... 13 2.4 LDP Discovery ..................................... 11
2.4.1 Basic Discovery Mechanism .......................... 13 2.4.1 Basic Discovery Mechanism .......................... 12
2.4.2 Extended Discovery Mechanism ....................... 14 2.4.2 Extended Discovery Mechanism ....................... 12
2.5 Establishing and Maintaining LDP Sessions .......... 15 2.5 Establishing and Maintaining LDP Sessions .......... 13
2.5.1 LDP Session Establishment .......................... 15 2.5.1 LDP Session Establishment .......................... 13
2.5.2 Transport Connection Establishment ................. 15 2.5.2 Transport Connection Establishment ................. 13
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 ....................... 17
2.5.5 Maintaining Hello Adjacencies ...................... 22 2.5.5 Maintaining Hello Adjacencies ...................... 20
2.5.6 Maintaining LDP Sessions ........................... 22 2.5.6 Maintaining LDP Sessions ........................... 20
2.6 Label Distribution and Management .................. 23 2.6 Label Distribution and Management .................. 21
2.6.1 Label Distribution Control Mode .................... 23 2.6.1 Label Distribution Control Mode .................... 21
2.6.1.1 Independent Label Distribution Control ............. 23 2.6.1.1 Independent Label Distribution Control ............. 21
2.6.1.2 Ordered Label Distribution Control ................. 23 2.6.1.2 Ordered Label Distribution Control ................. 21
2.6.2 Label Retention Mode ............................... 24 2.6.2 Label Retention Mode ............................... 22
2.6.2.1 Conservative Label Retention Mode .................. 24 2.6.2.1 Conservative Label Retention Mode .................. 22
2.6.2.2 Liberal Label Retention Mode ....................... 25 2.6.2.2 Liberal Label Retention Mode ....................... 22
2.6.3 Label Advertisement Mode ........................... 25 2.6.3 Label Advertisement Mode ........................... 23
2.7 LDP Identifiers and Next Hop Addresses ............. 25 2.7 LDP Identifiers and Next Hop Addresses ............. 23
2.8 Loop Detection ..................................... 26 2.8 Loop Detection ..................................... 24
2.8.1 Label Request Message .............................. 27 2.8.1 Label Request Message .............................. 24
2.8.2 Label Mapping Message .............................. 28 2.8.2 Label Mapping Message .............................. 26
2.8.3 Discussion ......................................... 30 2.8.3 Discussion ......................................... 27
2.9 Authenticity and Integrity of LDP Messages ......... 30 2.9 Authenticity and Integrity of LDP Messages ......... 28
2.9.1 TCP MD5 Signature Option ........................... 31 2.9.1 TCP MD5 Signature Option ........................... 28
2.9.2 LDP Use of TCP MD5 Signature Option ................ 32 2.9.2 LDP Use of TCP MD5 Signature Option ................ 30
2.10 Label Distribution for Explicitly Routed LSPs ...... 33 2.10 Label Distribution for Explicitly Routed LSPs ...... 30
3 Protocol Specification ............................. 33 3 Protocol Specification ............................. 31
3.1 LDP PDUs ........................................... 33 3.1 LDP PDUs ........................................... 31
3.2 LDP Procedures ..................................... 34 3.2 LDP Procedures ..................................... 32
3.3 Type-Length-Value Encoding ......................... 35 3.3 Type-Length-Value Encoding ......................... 32
3.4 TLV Encodings for Commonly Used Parameters ......... 36 3.4 TLV Encodings for Commonly Used Parameters ......... 34
3.4.1 FEC TLV ............................................ 36 3.4.1 FEC TLV ............................................ 34
3.4.1.1 FEC Procedures ..................................... 39 3.4.1.1 FEC Procedures ..................................... 37
3.4.2 Label TLVs ......................................... 39 3.4.2 Label TLVs ......................................... 37
3.4.2.1 Generic Label TLV .................................. 39 3.4.2.1 Generic Label TLV .................................. 37
3.4.2.2 ATM Label TLV ...................................... 40 3.4.2.2 ATM Label TLV ...................................... 38
3.4.2.3 Frame Relay Label TLV .............................. 40 3.4.2.3 Frame Relay Label TLV .............................. 38
3.4.3 Address List TLV ................................... 41 3.4.3 Address List TLV ................................... 39
3.4.4 Hop Count TLV ...................................... 42 3.4.4 Hop Count TLV ...................................... 40
3.4.4.1 Hop Count Procedures ............................... 42 3.4.4.1 Hop Count Procedures ............................... 40
3.4.5 Path Vector TLV .................................... 44 3.4.5 Path Vector TLV .................................... 41
3.4.5.1 Path Vector Procedures ............................. 44 3.4.5.1 Path Vector Procedures ............................. 42
3.4.5.1.1 Label Request Path Vector .......................... 44 3.4.5.1.1 Label Request Path Vector .......................... 42
3.4.5.1.2 Label Mapping Path Vector .......................... 45 3.4.5.1.2 Label Mapping Path Vector .......................... 43
3.4.6 Status TLV ......................................... 46 3.4.6 Status TLV ......................................... 43
3.5 LDP Messages ....................................... 47 3.5 LDP Messages ....................................... 45
3.5.1 Notification Message ............................... 50 3.5.1 Notification Message ............................... 47
3.5.1.1 Notification Message Procedures .................... 51 3.5.1.1 Notification Message Procedures .................... 48
3.5.1.2 Events Signaled by Notification Messages ........... 51 3.5.1.2 Events Signaled by Notification Messages ........... 49
3.5.1.2.1 Malformed PDU or Message ........................... 51 3.5.1.2.1 Malformed PDU or Message ........................... 49
3.5.1.2.2 Unknown or Malformed TLV ........................... 52 3.5.1.2.2 Unknown or Malformed TLV ........................... 50
3.5.1.2.3 Session KeepAlive Timer Expiration ................. 53 3.5.1.2.3 Session KeepAlive Timer Expiration ................. 50
3.5.1.2.4 Unilateral Session Shutdown ........................ 53 3.5.1.2.4 Unilateral Session Shutdown ........................ 51
3.5.1.2.5 Initialization Message Events ...................... 53 3.5.1.2.5 Initialization Message Events ...................... 51
3.5.1.2.6 Events Resulting From Other Messages ............... 53 3.5.1.2.6 Events Resulting From Other Messages ............... 51
3.5.1.2.7 Internal Errors .................................... 54 3.5.1.2.7 Internal Errors .................................... 51
3.5.1.2.8 Miscellaneous Events ............................... 54 3.5.1.2.8 Miscellaneous Events ............................... 51
3.5.2 Hello Message ...................................... 54 3.5.2 Hello Message ...................................... 51
3.5.2.1 Hello Message Procedures ........................... 56 3.5.2.1 Hello Message Procedures ........................... 54
3.5.3 Initialization Message ............................. 58 3.5.3 Initialization Message ............................. 55
3.5.3.1 Initialization Message Procedures .................. 66 3.5.3.1 Initialization Message Procedures .................. 63
3.5.4 KeepAlive Message .................................. 66 3.5.4 KeepAlive Message .................................. 63
3.5.4.1 KeepAlive Message Procedures ....................... 66 3.5.4.1 KeepAlive Message Procedures ....................... 63
3.5.5 Address Message .................................... 67 3.5.5 Address Message .................................... 64
3.5.5.1 Address Message Procedures ......................... 67 3.5.5.1 Address Message Procedures ......................... 64
3.5.6 Address Withdraw Message ........................... 68 3.5.6 Address Withdraw Message ........................... 65
3.5.6.1 Address Withdraw Message Procedures ................ 69 3.5.6.1 Address Withdraw Message Procedures ................ 66
3.5.7 Label Mapping Message .............................. 69 3.5.7 Label Mapping Message .............................. 66
3.5.7.1 Label Mapping Message Procedures ................... 70 3.5.7.1 Label Mapping Message Procedures ................... 67
3.5.7.1.1 Independent Control Mapping ........................ 70 3.5.7.1.1 Independent Control Mapping ........................ 67
3.5.7.1.2 Ordered Control Mapping ............................ 71 3.5.7.1.2 Ordered Control Mapping ............................ 68
3.5.7.1.3 Downstream on Demand Label Advertisement ........... 71 3.5.7.1.3 Downstream on Demand Label Advertisement ........... 68
3.5.7.1.4 Downstream Unsolicited Label Advertisement ......... 72 3.5.7.1.4 Downstream Unsolicited Label Advertisement ......... 69
3.5.8 Label Request Message .............................. 73 3.5.8 Label Request Message .............................. 69
3.5.8.1 Label Request Message Procedures ................... 74 3.5.8.1 Label Request Message Procedures ................... 70
3.5.9 Label Abort Request Message ........................ 75 3.5.9 Label Abort Request Message ........................ 72
3.5.9.1 Label Abort Request Message Procedures ............. 76 3.5.9.1 Label Abort Request Message Procedures ............. 73
3.5.10 Label Withdraw Message ............................. 77 3.5.10 Label Withdraw Message ............................. 74
3.5.10.1 Label Withdraw Message Procedures .................. 78 3.5.10.1 Label Withdraw Message Procedures .................. 75
3.5.11 Label Release Message .............................. 79 3.5.11 Label Release Message .............................. 76
3.5.11.1 Label Release Message Procedures ................... 80 3.5.11.1 Label Release Message Procedures ................... 77
3.6 Messages and TLVs for Extensibility ................ 81 3.6 Messages and TLVs for Extensibility ................ 78
3.6.1 LDP Vendor-private Extensions ...................... 81 3.6.1 LDP Vendor-private Extensions ...................... 78
3.6.1.1 LDP Vendor-private TLVs ............................ 81 3.6.1.1 LDP Vendor-private TLVs ............................ 78
3.6.1.2 LDP Vendor-private Messages ........................ 82 3.6.1.2 LDP Vendor-private Messages ........................ 80
3.6.2 LDP Experimental Extensions ........................ 84 3.6.2 LDP Experimental Extensions ........................ 81
3.7 Message Summary .................................... 84 3.7 Message Summary .................................... 81
3.8 TLV Summary ........................................ 85 3.8 TLV Summary ........................................ 82
3.9 Status Code Summary ................................ 86 3.9 Status Code Summary ................................ 83
3.10 Well-known Numbers ................................. 87 3.10 Well-known Numbers ................................. 84
3.10.1 UDP and TCP Ports .................................. 87 3.10.1 UDP and TCP Ports .................................. 84
3.10.2 Implicit NULL Label ................................ 87 3.10.2 Implicit NULL Label ................................ 84
4 IANA Considerations ................................ 87 4 IANA Considerations ................................ 84
4.1 Message Type Name Space ............................ 88 4.1 Message Type Name Space ............................ 84
4.2 TLV Type Name Space ................................ 88 4.2 TLV Type Name Space ................................ 85
4.3 FEC Type Name Space ................................ 89 4.3 FEC Type Name Space ................................ 85
4.4 Status Code Name Space ............................. 89 4.4 Status Code Name Space ............................. 86
4.5 Experiment ID Name Space ........................... 89 4.5 Experiment ID Name Space ........................... 86
5 Security Considerations ............................ 89 5 Security Considerations ............................ 86
5.1 Spoofing ........................................... 89 5.1 Spoofing ........................................... 86
5.2 Privacy ............................................ 90 5.2 Privacy ............................................ 87
5.3 Denial of Service .................................. 91 5.3 Denial of Service .................................. 87
6 Areas for Future Study ............................. 92 6 Areas for Future Study ............................. 89
7 Intellectual Property Considerations ............... 93 7 Intellectual Property Considerations ............... 89
8 Acknowledgments .................................... 93 8 Acknowledgments .................................... 89
9 References ......................................... 93 9 References ......................................... 89
10 Author Information ................................. 95 10 Authors' Addresses ................................. 92
Appendix A LDP Label Distribution Procedures .................. 93
Appendix A LDP Label Distribution Procedures .................. 96 A.1 Handling Label Distribution Events ................. 95
A.1 Handling Label Distribution Events ................. 98 A.1.1 Receive Label Request .............................. 96
A.1.1 Receive Label Request .............................. 99 A.1.2 Receive Label Mapping .............................. 99
A.1.2 Receive Label Mapping .............................. 102 A.1.3 Receive Label Abort Request ........................ 105
A.1.3 Receive Label Abort Request ........................ 108 A.1.4 Receive Label Release .............................. 107
A.1.4 Receive Label Release .............................. 110 A.1.5 Receive Label Withdraw ............................. 109
A.1.5 Receive Label Withdraw ............................. 112 A.1.6 Recognize New FEC .................................. 110
A.1.6 Recognize New FEC .................................. 113 A.1.7 Detect Change in FEC Next Hop ...................... 113
A.1.7 Detect Change in FEC Next Hop ...................... 116 A.1.8 Receive Notification / Label Request Aborted ....... 116
A.1.8 Receive Notification / Label Request Aborted ....... 119 A.1.9 Receive Notification / No Label Resources .......... 116
A.1.9 Receive Notification / No Label Resources .......... 119 A.1.10 Receive Notification / No Route .................... 117
A.1.10 Receive Notification / No Route .................... 120 A.1.11 Receive Notification / Loop Detected ............... 118
A.1.11 Receive Notification / Loop Detected ............... 121 A.1.12 Receive Notification / Label Resources Available ... 118
A.1.12 Receive Notification / Label Resources Available ... 122 A.1.13 Detect local label resources have become available . 119
A.1.13 Detect local label resources have become available . 122 A.1.14 LSR decides to no longer label switch a FEC ........ 120
A.1.14 LSR decides to no longer label switch a FEC ........ 123 A.1.15 Timeout of deferred label request .................. 121
A.1.15 Timeout of deferred label request .................. 124 A.2 Common Label Distribution Procedures ............... 121
A.2 Common Label Distribution Procedures ............... 125 A.2.1 Send_Label ......................................... 121
A.2.1 Send_Label ......................................... 125 A.2.2 Send_Label_Request ................................. 123
A.2.2 Send_Label_Request ................................. 126 A.2.3 Send_Label_Withdraw ................................ 124
A.2.3 Send_Label_Withdraw ................................ 128 A.2.4 Send_Notification .................................. 125
A.2.4 Send_Notification .................................. 128 A.2.5 Send_Message ....................................... 125
A.2.5 Send_Message ....................................... 129 A.2.6 Check_Received_Attributes .......................... 126
A.2.6 Check_Received_Attributes .......................... 129 A.2.7 Prepare_Label_Request_Attributes ................... 127
A.2.7 Prepare_Label_Request_Attributes ................... 131 A.2.8 Prepare_Label_Mapping_Attributes ................... 129
A.2.8 Prepare_Label_Mapping_Attributes ................... 132 Full Copyright Statement ...................................... 132
1. LDP Overview 1. LDP Overview
The MPLS architecture [ARCH] defines a label distribution protocol as The MPLS architecture [RFC3031] defines a label distribution protocol
a set of procedures by which one Label Switched Router (LSR) informs as a set of procedures by which one Label Switched Router (LSR)
another of the meaning of labels used to forward traffic between and informs another of the meaning of labels used to forward traffic
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 protocol. In fact, a number of different label distribution
protocols are being standardized. Existing protocols have been protocols are being standardized. Existing protocols have been
extended so that label distribution can be piggybacked on them. New extended so that label distribution can be piggybacked on them. New
protocols have also been defined for the explicit purpose of protocols have also been defined for the explicit purpose of
distributing labels. The MPLS architecture discusses some of the distributing labels. The MPLS architecture discusses some of the
considerations when choosing a label distribution protocol for use in considerations when choosing a label distribution protocol for use in
particular MPLS applications such as Traffic Engineering [TE]. particular MPLS applications such as Traffic Engineering [RFC2702].
The Label Distribution Protocol (LDP) defined in this document is a The Label Distribution Protocol (LDP) defined in this document is a
new protocol defined for distributing labels. It is the set of new protocol defined for distributing labels. It is the set of
procedures and messages by which Label Switched Routers (LSRs) procedures and messages by which Label Switched Routers (LSRs)
establish Label Switched Paths (LSPs) through a network by mapping establish Label Switched Paths (LSPs) through a network by mapping
network-layer routing information directly to data-link layer network-layer routing information directly to data-link layer
switched paths. These LSPs may have an endpoint at a directly switched paths. These LSPs may have an endpoint at a directly
attached neighbor (comparable to IP hop-by-hop forwarding), or may attached neighbor (comparable to IP hop-by-hop forwarding), or may
have an endpoint at a network egress node, enabling switching via all have an endpoint at a network egress node, enabling switching via all
intermediary nodes. intermediary nodes.
LDP associates a Forwarding Equivalence Class (FEC) [ARCH] with each LDP associates a Forwarding Equivalence Class (FEC) [RFC3031] with
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 packets are "mapped" to that LSP. LSPs are extended through a
network as each LSR "splices" incoming labels for a FEC to the network as each LSR "splices" incoming labels for a FEC to the
outgoing 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
[LDPAPPLIC]. [RFC3037].
This document assumes familiarity with the MPLS architecture [ARCH]. This document assumes familiarity with the MPLS architecture
Note that [ARCH] includes a glossary of MPLS terminology, such as [RFC3031]. Note that [RFC3031] includes a glossary of MPLS
ingress, label switched path, etc. 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 which 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 of
there being an "LDP Session" between them. A single LDP session there being an "LDP Session" between them. A single LDP session
allows each peer to learn the other's label mappings; i.e., the allows each peer to learn the other's label mappings; i.e., the
protocol is bi-directional. protocol is bi-directional.
1.2. LDP Message Exchange 1.2. LDP Message Exchange
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(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
backwards compatible, some prior planning can ease the introduction backwards compatible, some prior planning can ease the introduction
of new capabilities. This specification defines rules for handling of new capabilities. This specification defines rules for handling
unknown message types and unknown TLVs for this purpose. unknown message types and unknown TLVs for this purpose.
1.6. Specification Language 1.6. Specification Language
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 which may be mapped to
that LSP. that LSP.
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say that a particular packet matches a particular LSP if and only if say that a particular packet matches a particular LSP if and only if
that LSP has an Address Prefix FEC element which matches the packet's that LSP has an Address Prefix FEC element which matches the packet's
destination address. With respect to a particular packet and a destination address. With respect to a particular packet and a
particular LSP, we refer to any Address Prefix FEC element which particular LSP, we refer to any Address Prefix FEC element which
matches the 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 there is exactly one LSP which has a Host Address FEC element - If there is exactly one LSP which has a Host Address FEC
that is identical to the packet's destination address, then the element that is identical to the packet's destination address,
packet is mapped to that LSP. then the packet is mapped to that LSP.
- If there are multiple LSPs, each containing a Host Address FEC - If there are multiple LSPs, each containing a Host Address FEC
element that is identical to the packet's destination address, element that is identical to the packet's destination address,
then the packet is mapped to one of those LSPs. The procedure then the packet is mapped to one of those LSPs. The procedure
for selecting one of those LSPs is beyond the scope of this for selecting one of those LSPs is beyond the scope of this
document. document.
- 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 router, and there is an LSP which has an Address Prefix FEC
element which is an address of that router, then the packet is element which is an address of that router, then the packet is
mapped to that LSP. The procedure for obtaining this knowledge mapped to that LSP. The procedure for obtaining this knowledge
is beyond the scope of this document. is beyond the scope of this document.
The procedure for determining that a packet must traverse a The procedure for determining that a packet must traverse a
particular egress router is beyond the scope of this document. (As particular egress router is beyond the scope of this document. (As
an example, if one is running a link state routing algorithm, it may an example, if one is running a link state routing algorithm, it may
be possible to obtain this information from the link state data base. be possible to obtain this information from the link state data base.
As another example, if one is running BGP, it may be possible to As another example, if one is running BGP, it may be possible to
obtain this information from the BGP next hop attribute of the obtain this information from the BGP next hop attribute of the
packet's route.) packet's route.)
It is worth pointing out a few consequences of these rules: It is worth pointing out a few consequences of these rules:
- A packet may be sent on the LSP whose Address Prefix FEC element - A packet may be sent on the LSP whose Address Prefix FEC
is the address of the packet's egress router ONLY if there is no element is the address of the packet's egress router ONLY if
LSP matching the packet's destination address. there is no LSP matching the packet's destination address.
- A packet may match two LSPs, one with a Host Address FEC element - A packet may match two LSPs, one with a Host Address FEC
and one with an Address Prefix FEC element. In this case, the element and one with an Address Prefix FEC element. In this
packet is always assigned to the former. case, the packet is always assigned to the former.
- A packet which does not match a particular Host Address FEC - A packet which does not match a particular Host Address FEC
element may not be sent on the corresponding LSP, even if the element may not be sent on the corresponding LSP, even if the
Host Address FEC element identifies the packet's egress router. Host Address FEC element identifies the packet's egress router.
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 labels. An example of such an interface is a label-controlled
interface that uses VCIs as labels, or a Frame Relay interface ATM interface that uses VCIs as labels, or a Frame Relay
that uses DLCIs as labels. interface that uses DLCIs 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.
Note that an LSR that manages and advertises multiple label spaces Note that an LSR that manages and advertises multiple label spaces
uses a different LDP Identifier for each such label space. uses a different LDP Identifier for each such label space.
A situation where an LSR would need to advertise more than one label A situation where an LSR would need to advertise more than one label
space to a peer and hence use more than one LDP Identifier occurs space to a peer and hence use more than one LDP Identifier occurs
when the LSR has two links to the peer and both are ATM (and use per when the LSR has two links to the peer and both are ATM (and use per
interface labels). Another situation would be where the LSR had two interface labels). Another situation would be where the LSR had two
skipping to change at page 13, line 39 skipping to change at page 11, line 46
label 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 LDP discovery is a mechanism that enables an LSR to discover
potential LDP peers. Discovery makes it unnecessary to explicitly potential LDP peers. Discovery makes it unnecessary to explicitly
configure 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
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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 1. If LSR1 does not already have an LDP session for the exchange
of label spaces LSR1:a and LSR2:b it attempts to open a TCP of label spaces LSR1:a and LSR2:b it attempts to open a TCP
connection 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 Hello's 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 - Let U1 be the abstract unsigned integer obtained by treating
treating A1 as a sequence of bytes, where the byte which A1 as a sequence of bytes, where the byte which appears
appears earliest in the message is the most significant earliest in the message is the most significant byte of the
byte of the integer and the byte which appears latest in integer and the byte which appears latest in the message is
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 3. If LSR1 is active, it attempts to establish the LDP TCP
connection by connecting to the well-known LDP port at address connection by connecting to the well-known LDP port at address
A2. If LSR1 is passive, it waits for LSR2 to establish the LDP A2. If LSR1 is passive, it waits for LSR2 to establish the LDP
TCP 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 the address, either explicitly by including it in an optional
Transport Address TLV or implicitly by omitting the TLV and using it Transport Address TLV or implicitly by omitting the TLV and using it
as the Hello source address. as the Hello source address.
skipping to change at page 17, line 27 skipping to change at page 15, line 31
the connection. The Initialization message carries both the LDP the connection. The Initialization message carries both the LDP
Identifier for the sender's (active LSR's) label space and the LDP Identifier for the sender's (active LSR's) label space and the LDP
Identifier 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 LSR can match the label space to be advertised by the peer (as
determined from the LDP Identifier in the PDU header for the determined from the LDP Identifier in the PDU header for the
Initialization message) with a Hello adjacency previously created Initialization message) with a Hello adjacency previously created
when Hellos 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 b. If there is a matching Hello adjacency, the adjacency
specifies 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 an Initialization message of its own to propose the
parameters it wishes to use and a KeepAlive message to parameters it wishes to use and a KeepAlive message to
signal acceptance of LSR2's parameters. If the parameters signal acceptance of LSR2's parameters. If the parameters
are not 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 d. If LSR1 receives a KeepAlive in response to its
Initialization message, the session is operational from Initialization message, the session is operational from
LSR1's point 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 rejected its proposed session and LSR1 closes the TCP
connection. 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 rejected its proposed session and LSR1 closes the TCP
connection. 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 replies with a KeepAlive message. If the session parameters
parameters are unacceptable, LSR1 sends a Session are unacceptable, LSR1 sends a Session Rejected/Parameters
Rejected/Parameters Error Notification message and closes Error Notification message and closes the connection.
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.
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 Notification messages. Error 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 being NAK'd. It is also recommended that an LSR detecting are being NAK'd. It is also recommended that an LSR detecting
such a situation take action to notify an operator. such a situation take action to notify an operator.
The session establishment setup attempt following a NAK'd The session establishment setup attempt following a NAK'd
Initialization message must be delayed no less than 15 seconds, Initialization message must be delayed no less than 15 seconds,
and subsequent delays must grow to a maximum delay of no less and subsequent delays must grow to a maximum delay of no less than
than 2 minutes. The specific session establishment action that 2 minutes. The specific session establishment action that must be
must be delayed is the attempt to open the session transport delayed is the attempt to open the session transport connection by
connection 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
After such a configuration action there is no further need to such a configuration action there is no further need to throttle
throttle subsequent session establishment attempts (until their subsequent session establishment attempts (until their
initialization messages are NAK'd). initialization messages are NAK'd).
Due to the asymmetric nature of session establishment, Due to the asymmetric nature of session establishment,
reconfiguration of the passive LSR will go unnoticed by the reconfiguration of the passive LSR will go unnoticed by the active
active LSR without some further action. Section "Hello Message" LSR without some further action. Section "Hello Message"
describes an optional mechanism an LSR can use to signal describes an optional mechanism an LSR can use to signal potential
potential LDP peers that it has been reconfigured. LDP peers 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. table and as a state transition diagram.
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)
Receive acceptable OPENREC Receive acceptable OPENREC
Initialization msg Initialization msg
(Passive Role ) (Passive Role )
Action: Transmit Initialization Action: Transmit Initialization
msg and KeepAlive msg msg and KeepAlive msg
Receive Any other LDP msg NON EXISTENT Receive Any other LDP msg NON EXISTENT
Action: Transmit Error Notification msg Action: Transmit Error Notification msg
(NAK) and close transport connection (NAK) and close transport connection
OPENREC Receive KeepAlive msg OPERATIONAL OPENREC Receive KeepAlive msg OPERATIONAL
Receive Any other LDP msg NON EXISTENT Receive Any other LDP msg NON EXISTENT
Action: Transmit Error Notification msg Action: Transmit Error Notification msg
(NAK) and close transport connection (NAK) and close transport connection
OPENSENT Receive acceptable OPENREC OPENSENT Receive acceptable OPENREC
Initialization msg Initialization msg
Action: Transmit KeepAlive msg Action: Transmit KeepAlive msg
Receive Any other LDP msg NON EXISTENT Receive Any other LDP msg NON EXISTENT
Action: Transmit Error Notification msg Action: Transmit Error Notification msg
(NAK) and close transport connection (NAK) and close transport connection
OPERATIONAL Receive Shutdown msg NON EXISTENT OPERATIONAL Receive Shutdown msg NON EXISTENT
Action: Transmit Shutdown msg and Action: Transmit Shutdown msg and
close transport connection close transport connection
Receive other LDP msgs OPERATIONAL Receive other LDP msgs OPERATIONAL
Timeout NON EXISTENT Timeout NON EXISTENT
Action: Transmit Shutdown msg and Action: Transmit Shutdown msg and
close transport connection close transport connection
Session Initialization State Transition Diagram Session Initialization State Transition Diagram
+------------+ +------------+
| | | |
+------------>|NON EXISTENT|<--------------------+ +------------>|NON EXISTENT|<--------------------+
| | | | | | | |
| +------------+ | | +------------+ |
| Session | ^ | | Session | ^ |
| connection | | | | connection | | |
| established | | Rx any LDP msg except | | established | | Rx any LDP msg except |
| V | Init msg or Timeout | | V | Init msg or Timeout |
| +-----------+ | | +-----------+ |
Rx Any other | | | | Rx Any other | | | |
msg or | |INITIALIZED| | msg or | |INITIALIZED| |
Timeout / | +---| |-+ | Timeout / | +---| |-+ |
Tx NAK msg | | +-----------+ | | Tx NAK msg | | +-----------+ | |
| | (Passive Role) | (Active Role) | | | (Passive Role) | (Active Role) |
| | Rx Acceptable | Tx Init msg | | | Rx Acceptable | Tx Init msg |
| | Init msg / | | | | Init msg / | |
| | Tx Init msg | | | | Tx Init msg | |
| | Tx KeepAlive | | | | Tx KeepAlive | |
| V msg V | | V msg V |
| +-------+ +--------+ | | +-------+ +--------+ |
| | | | | | | | | | | |
+---|OPENREC| |OPENSENT|----------------->| +---|OPENREC| |OPENSENT|----------------->|
+---| | | | Rx Any other msg | +---| | | | Rx Any other msg |
| +-------+ +--------+ or Timeout | | +-------+ +--------+ or Timeout |
Rx KeepAlive | ^ | Tx NAK msg | Rx KeepAlive | ^ | Tx NAK msg |
msg | | | | msg | | | |
| | | Rx Acceptable | | | | Rx Acceptable |
| | | Init msg / | | | | Init msg / |
| +----------------+ Tx KeepAlive msg | | +----------------+ Tx KeepAlive msg |
| | | |
| +-----------+ | | +-----------+ |
+----->| | | +----->| | |
|OPERATIONAL| | |OPERATIONAL| |
| |---------------------------->+ | |---------------------------->+
+-----------+ Rx Shutdown msg +-----------+ Rx Shutdown msg
All other | ^ or Timeout / All other | ^ or Timeout /
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 example, multiple PPP links between a pair of routers. In this
situation the Hellos an LSR sends on each such link carry the same situation the Hellos an LSR sends on each such link carry the same
LDP Identifier. LDP Identifier.
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it terminates the LDP session by closing the transport connection. 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 LSR may send any protocol message to meet this requirement. In
circumstances 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 [ARCH] allows an LSR to distribute a FEC label The MPLS architecture [RF3031] allows an LSR to distribute a FEC
binding in response to an explicit request from another LSR. This is label binding in response to an explicit request from another LSR.
known as Downstream On Demand label distribution. It also allows an This is known as Downstream On Demand label distribution. It also
LSR to distribute label bindings to LSRs that have not explicitly allows an LSR to distribute label bindings to LSRs that have not
requested them. [ARCH] calls this method of label distribution explicitly requested them. [RFC3031] calls this method of label
Unsolicited Downstream; this document uses the term Downstream distribution Unsolicited Downstream; this document uses the term
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 in order to avoid situations where one peer using Downstream
Unsolicited 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
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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 2. The next hop router for the FEC is outside of the Label
Switching Network. Switching Network.
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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 2. The next hop router for the FEC is outside of the Label
Switching Network. Switching Network.
3. FEC elements are reachable by crossing a routing domain 3. FEC elements are reachable by crossing a routing domain
boundary, such as another area for OSPF summary networks, or boundary, such as another area for OSPF summary networks, or
another autonomous system for OSPF AS externals and BGP routes another autonomous system for OSPF AS externals and BGP routes
[rfc1583] [rfc1771]. [RFC2328] [RFC1771].
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 [ARCH] introduces the notion of label retention The MPLS architecture [RFC3031] introduces the notion of label
mode which specifies whether an LSR maintains a label binding for a retention mode which specifies whether an LSR maintains a label
FEC learned from a neighbor that is not its next hop for the FEC. binding for a FEC learned from a neighbor that is not its next hop
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 In Downstream Unsolicited advertisement mode, label mapping
advertisements for all routes may be received from all peer LSRs. advertisements for all routes may be received from all peer LSRs.
When using conservative label retention, advertised label mappings When using conservative label retention, advertised label mappings
are retained only if they will be used to forward packets (i.e., if are retained only if they will be used to forward packets (i.e., if
they are received from a valid next hop according to routing). If they are received from a valid next hop according to routing). If
operating in Downstream on Demand mode, an LSR will request label operating in Downstream on Demand mode, an LSR will request label
mappings only from the next hop LSR according to routing. Since mappings only from the next hop LSR according to routing. Since
Downstream on Demand mode is primarily used when label conservation Downstream on Demand mode is primarily used when label conservation
is desired (e.g., an ATM switch with limited cross connect space), it is desired (e.g., an ATM switch with limited cross connect space), it
is typically 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 that are required for the forwarding of data are allocated and
maintained. This is particularly important in LSRs where the label maintained. This is particularly important in LSRs where the label
space is inherently limited, such as in an ATM switch. A space is inherently limited, such as in an ATM switch. A
disadvantage of the conservative mode is that if routing changes the disadvantage of the conservative mode is that if routing changes the
next hop for a given destination, a new label must be obtained from next hop for a given destination, a new label must be obtained from
skipping to change at page 26, line 24 skipping to change at page 24, line 19
2.8. Loop Detection 2.8. Loop Detection
Loop detection is a configurable option which provides a mechanism Loop detection is a configurable option which provides a mechanism
for finding looping LSPs and for preventing Label Request messages for finding looping LSPs and for preventing Label Request messages
from looping in the presence of non-merge capable LSRs. from 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 propagates a message containing a Path Vector TLV it adds its
Vector list. An LSR that receives a message with a Path Vector LSR Id to the Path Vector list. An LSR that receives a message
that 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 containing message has traversed. When an LSR propagates a
containing a Hop Count TLV it increments the count. An LSR that message containing a Hop Count TLV it increments the count. An
detects a Hop Count has reached a configured maximum value LSR that detects a Hop Count has reached a configured maximum
behaves as if the containing message has traversed a loop. By value behaves as if the containing message has traversed a
convention a count of 0 is interpreted to mean the hop count is loop. By convention a count of 0 is interpreted to mean the
unknown. Incrementing an unknown hop count value results in an hop count is unknown. Incrementing an unknown hop count value
unknown hop count value (0). results in an unknown hop count value (0).
The following paragraphs describes LDP loop detection procedures. The following paragraphs describes LDP loop detection procedures.
For these paragraphs, and only these paragraphs, "MUST" is redfined For these paragraphs, and only these paragraphs, "MUST" is redefined
to mean "MUST if configured for loop detection". The paragraphs to mean "MUST if configured for loop detection". The paragraphs
specify messages that must carry Path Vector and Hop Count TLVs. specify messages that must carry Path Vector and Hop Count TLVs.
Note that the Hop Count TLV and its procedures are used without the Note that the Hop Count TLV and its procedures are used without the
Path Vector TLV in situations when loop detection is not configured Path Vector TLV in situations when loop detection is not configured
(see [ATM] and [FR]). (see [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 The rules that govern use of the Hop Count 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:
- 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, then - If R is sending the Label Request because it is a FEC ingress,
if R is non-merge capable, it MUST include a Path Vector TLV of then if R is non-merge capable, it MUST include a Path Vector TLV
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 a - If R is sending the Label Request as a result of having received 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 the R MUST add its own LSR Id to the Path Vector, and MUST pass the
resulting Path Vector to its next hop along with the Label resulting Path Vector to its next hop along with the Label
Request message. If the Label Request contains no Path Vector Request message. If the Label Request contains no Path Vector
TLV, R MUST include a Path Vector TLV of length 1 containing TLV, R MUST include a Path Vector TLV of length 1 containing
its own LSR Id. its own LSR Id.
Note that if R receives a Label Request message for a particular FEC, Note that if R receives a Label Request message for a particular FEC,
and R has previously sent a Label Request message for that FEC to its and R has previously sent a Label Request message for that FEC to its
next hop and has not yet received a reply, and if R intends to merge next hop and has not yet received a reply, and if R intends to merge
skipping to change at page 28, line 21 skipping to change at page 26, line 17
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 messages sent by an LSR R when Loop Detection is enabled are the
following: 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 Label - If the Label Mapping message is not being sent to propagate a
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 messages sent by LSR R when Loop Detection is enabled are the
following: 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
Path Vector TLV. Path Vector TLV.
o If the received message contains an unknown hop count, then R o If the received message contains an unknown hop count, then R
MUST include a Path Vector TLV. MUST include a Path Vector TLV.
o If R has previously sent a Label Mapping message to the o If R has previously sent a Label Mapping message to the
upstream peer, then it MUST include a Path Vector TLV if the upstream peer, then it MUST include a Path Vector TLV if the
received message reports an LSP hop count increase, a change in received message reports an LSP hop count increase, a change in
hop count from unknown to known, or a change from known to hop count from unknown to known, or a change from known to
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
Mapping message, R computes it as follows: Label 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 include a received message upstream, the Label Mapping message MUST include
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 Hop If R receives a Label Mapping message from its next hop with a Hop
Count TLV which exceeds the configured maximum value, or with a Path Count TLV which exceeds the configured maximum value, or with a Path
Vector TLV containing its own LSR Id or which exceeds the maximum Vector TLV containing its own LSR Id or which exceeds the maximum
allowable length, then R detects that the corresponding LSP contains allowable length, then R detects that the corresponding LSP contains
a loop. a loop.
When R detects a loop, it MUST stop using the label for forwarding, When R detects a loop, it MUST stop using the label for forwarding,
drop the Label Mapping message, and signal Loop Detected status to drop the Label Mapping message, and signal Loop Detected status to
the source of the Label Mapping message. the source of the Label Mapping message.
skipping to change at page 30, line 43 skipping to change at page 28, line 33
number 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 This section specifies a mechanism to protect against the
introduction of spoofed TCP segments into LDP session connection introduction of spoofed TCP segments into LDP session connection
streams. The use of this mechanism MUST be supported as a streams. The use of this mechanism MUST be supported as a
configurable option. configurable option.
The mechanism is based on use of the TCP MD5 Signature Option The mechanism is based on use of the TCP MD5 Signature Option
specified in [rfc2385] for use by BGP. See [rfc1321] for a specified in [RFC2385] for use by BGP. See [RFC1321] for a
specification of the MD5 hash function. specification of the MD5 hash function.
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 summarizes 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
skipping to change at page 32, line 25 skipping to change at page 30, line 13
limited option space. limited option space.
This does not prevent the deployment of another similar option This does not prevent the deployment of another similar option
which uses another hashing algorithm (like SHA-1). Also, if which uses another hashing algorithm (like SHA-1). Also, if
most implementations pad the 18 byte option as defined to 20 most implementations pad the 18 byte option as defined to 20
bytes anyway, it would be just as well to define a new option bytes anyway, it would be just as well to define a new option
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 - Use of the MD5 Signature Option for LDP TCP connections is a
configurable 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 - When the LSR receives a TCP segment with an MD5 digest, it
validates the segment by calculating the MD5 digest (using its validates the segment by calculating the MD5 digest (using its
own record of the password) and compares the computed digest with own record of the password) and compares the computed digest
the received digest. If the comparison fails, the segment is with the received digest. If the comparison fails, the segment
dropped 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 LDP TCP connections only with LSRs for which a password has
configured. been configured.
2.10. Label Distribution for Explicitly Routed LSPs 2.10. Label Distribution for Explicitly Routed LSPs
Traffic Engineering [TE] 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 Previous sections that describe LDP operation have discussed
scenarios that involve the exchange of messages among LDP peers. scenarios that involve the exchange of messages among LDP peers.
skipping to change at page 34, line 4 skipping to change at page 31, line 36
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 Two octet unsigned integer containing the version number of the
protocol. This version of the specification specifies LDP protocol protocol. This version of the specification specifies LDP protocol
version 1. version 1.
PDU Length PDU Length
Two octet integer specifying the total length of this PDU in Two octet integer specifying the total length of this PDU in
octets, 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 The maximum allowable PDU Length is negotiable when an LDP session
is initialized. Prior to completion of the negotiation the maximum is initialized. Prior to completion of the negotiation the maximum
allowable length is 4096 bytes. allowable length is 4096 bytes.
LDP Identifier LDP Identifier
Six octet field that uniquely identifies the label space of the Six octet field that uniquely identifies the label space of the
sending LSR for which this PDU applies. The first four octets sending LSR for which this PDU applies. The first four octets
identify the LSR and must be a globally unique value. It should be identify the LSR and must be a globally unique value. It should be
a 32-bit router Id assigned to the LSR and also used to identify it a 32-bit router Id assigned to the LSR and also used to identify it
in loop detection Path Vectors. The last two octets identify a in loop detection Path Vectors. The last two octets identify a
label space within the LSR. For a platform-wide label space, these label space within the LSR. For a platform-wide label space, these
should both be zero. 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 describe fully, coherently and unambiguously as a collection of
separate 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
skipping to change at page 35, line 29 skipping to change at page 33, line 19
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| 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 and (=0), a notification must be returned to the message originator
the entire message must be ignored; if U is set (=1), the unknown and the entire message must be ignored; if U is set (=1), the
TLV is silently ignored and the rest of the message is processed as unknown TLV is silently ignored and the rest of the message is
if the unknown TLV did not exist. The sections following that processed as if the unknown TLV did not exist. The sections
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 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. The sections following that forwarded with the containing message. The sections following
define TLVs specify a value for the F-bit. that define TLVs specify a value for the F-bit.
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 appearing in an LDP PDU could be encoded as a TLV. This
specification does not use the TLV scheme to its full generality. It specification does not use the TLV scheme to its full generality. It
skipping to change at page 36, line 46 skipping to change at page 34, line 35
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
There are several parameters used by more than one LDP message. The There are several parameters used by more than one LDP message. The
TLV encodings for these commonly used parameters are specified in TLV encodings for these commonly used parameters are specified in
this section. this section.
3.4.1. FEC TLV 3.4.1. FEC TLV
Labels are bound to Forwarding Equivalence Classes (FECs). a FEC is Labels are bound to Forwarding Equivalence Classes (FECs). A FEC is
a list of one or more FEC elements. The FEC TLV encodes FEC items. a list of one or more FEC elements. The FEC TLV encodes FEC items.
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| FEC (0x0100) | Length | |0|0| FEC (0x0100) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element 1 | | FEC Element 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element n | | FEC Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
FEC Element 1 to FEC Element n FEC Element 1 to FEC Element n
There are several types of FEC elements; see Section "FECs". The There are several types of FEC elements; see Section "FECs". The
FEC element encoding depends on the type of FEC element. FEC element encoding depends on the type of FEC element.
A FEC Element value is encoded as a 1 octet field that specifies A FEC Element value is encoded as a 1 octet field that specifies
the element type, and a variable length field that is the type- the element type, and a variable length field that is the type-
dependent element value. Note that while the representation of the dependent element value. Note that while the representation of
FEC element value is type-dependent, the FEC element encoding the FEC element value is type-dependent, the FEC element encoding
itself is one where standard LDP TLV encoding is not used. itself is one where standard LDP TLV encoding is not used.
The FEC Element value encoding is: The FEC Element value encoding is:
FEC Element Type Value FEC Element Type Value
type name type name
Wildcard 0x01 No value; i.e., 0 value octets; Wildcard 0x01 No value; i.e., 0 value octets;
see below. see below.
Prefix 0x02 See below. Prefix 0x02 See below.
Host Address 0x03 Full host address; see below. Host Address 0x03 Full host address; 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 Messages. To be used only in the Label Withdraw and Label Release
Indicates the withdraw/release is to be applied to all FECs Messages. Indicates the withdraw/release is to be applied to
associated with the label within the following label TLV. Must all FECs associated with the label within the following label
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 Two octet quantity containing a value from ADDRESS FAMILY
NUMBERS in [rfc1700] that encodes the address family for the NUMBERS in [RFC1700] that encodes the address family for the
address prefix in the Prefix field. 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 the
address prefix that follows. A length of zero indicates a address prefix that follows. A length of zero indicates a
prefix that matches all addresses (the default destination); in prefix that matches all addresses (the default destination); in
this case the Prefix itself is zero octets). 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.
Host Address FEC Element encoding: Host Address FEC Element 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Host Addr (3) | Address Family | Host Addr Len | | Host Addr (3) | Address Family | Host Addr Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Host Addr | | Host Addr |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Family Address Family
Two octet quantity containing a value from ADDRESS FAMILY Two octet quantity containing a value from ADDRESS FAMILY
NUMBERS in [rfc1700] that encodes the address family for the NUMBERS in [RFC1700] that encodes the address family for the
address prefix in the Prefix field. address prefix in the Prefix field.
Host Addr Len Host Addr Len
Length of the Host address in octets. Length of the Host address in octets.
Host Addr Host Addr
An address encoded according to the Address Family field. An address encoded according to the Address Family field.
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
TLV, abort processing the message containing the TLV, and send an TLV, abort processing the message containing the TLV, and send an
"Unsupported Address Family" Notification message to its LDP peer "Unsupported Address Family" Notification message to its LDP peer
signaling an error. signaling an error.
skipping to change at page 39, line 42 skipping to change at page 37, line 41
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| Generic Label (0x0200) | Length | |0|0| Generic Label (0x0200) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Label Label
This is a 20-bit label value as specified in [ENCAP] represented as This is a 20-bit label value as specified in [RFC3032] represented
a 20-bit number in a 4 octet field. as a 20-bit number in a 4 octet field.
3.4.2.2. ATM Label TLV 3.4.2.2. ATM Label TLV
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 and This field is reserved. It must be set to zero on transmission
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 VCI Two-bit switching indicator. If V-bits is 00, both the VPI and
are significant. If V-bits is 01, only the VPI field is VCI are significant. If V-bits is 01, only the VPI field is
significant. 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
field, then this field must be ignored by the receiver and set to 0 field, then this field must be ignored by the receiver and set to
by the sender. 0 by the sender.
3.4.2.3. Frame Relay Label TLV 3.4.2.3. Frame Relay Label TLV
An LSR uses Frame Relay Label TLVs to encode labels for use on Frame An LSR uses Frame Relay Label TLVs to encode labels for use on Frame
Relay links. Relay 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| 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 and This field is reserved. It must be set to zero on transmission
must be ignored on receipt. and must be ignored on receipt.
Len Len
This field specifies the number of bits of the DLCI. The following This field specifies the number of bits of the DLCI. The
values are supported: following values are supported:
0 = 10 bits DLCI 0 = 10 bits DLCI
2 = 23 bits DLCI 2 = 23 bits DLCI
Len values 1 and 3 are reserved. Len values 1 and 3 are reserved.
DLCI DLCI
The Data Link Connection Identifier. Refer to [FR] for the label The Data Link Connection Identifier. Refer to [RFC3034] for the
values and formats. label values and formats.
3.4.3. Address List TLV 3.4.3. Address List TLV
The Address List TLV appears in Address and Address Withdraw The Address List TLV appears in Address and Address Withdraw
messages. 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
skipping to change at page 41, line 42 skipping to change at page 39, line 42
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family | | | Address Family | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| Addresses | | Addresses |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Family Address Family
Two octet quantity containing a value from ADDRESS FAMILY NUMBERS Two octet quantity containing a value from ADDRESS FAMILY NUMBERS
in [rfc1700] that encodes the addresses contained in the Addresses in [RFC1700] that encodes the addresses contained in the Addresses
field. field.
Addresses Addresses
A list of addresses from the specified Address Family. The A list of addresses from the specified Address Family. The
encoding of the individual addresses depends on the Address Family. encoding of the individual addresses depends on the Address Family.
The following address encodings are defined by this version of the The following address encodings are defined by this version of the
protocol: protocol:
Address Family Address Encoding Address Family Address Encoding
IPv4 4 octet full IPv4 address IPv4 4 octet full IPv4 address
IPv6 16 octet full IPv6 address
3.4.4. Hop Count TLV 3.4.4. Hop Count TLV
The Hop Count TLV appears as an optional field in messages that set The Hop Count TLV appears as an optional field in messages that set
up LSPs. It calculates the number of LSR hops along an LSP as the up LSPs. It calculates the number of LSR hops along an LSP as the
LSP is being setup. LSP is being setup.
Note that setup procedures for LSPs that traverse ATM and Frame Relay Note that setup procedures for LSPs that traverse ATM and Frame Relay
links require use of the Hop Count TLV (see [ATM] and [FR]). links require use of the Hop Count TLV (see [RFC3035] and [RFC3034]).
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| 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 must determine a hop count to include continue the LSP setup, it must must determine a hop count to include
in the propagated message as follows: in 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;
- If the message is a Label Mapping message, R determines the hop - If the message is a Label Mapping message, R determines the hop
count as follows: count 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' and the upstream peer is within that not perform 'TTL-decrement' and the upstream peer is within
domain, R must reset the hop count to 1 before propagating the that domain, R must reset the hop count to 1 before propagating
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 overhead when independent control is used. When a new LSP is
skipping to change at page 44, line 31 skipping to change at page 42, line 25
| 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 the traversed. Each LSR Id is the first four octets (router-id) of
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.
skipping to change at page 46, line 27 skipping to change at page 44, line 20
|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 Fatal error bit. If set (=1), this is a fatal error
notification. 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 any, to the LSR for the next-hop or previous-hop for the LSP, if
associated with the event being signaled. If clear (=0), the any, associated with the event being signaled. If clear (=0),
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 which specifies the status information.
This specification defines Status Codes (32-bit unsigned integers This specification defines Status Codes (32-bit unsigned integers
with the above encoding). 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 which If non-zero, 32-bit value that identifies the peer message to
the Status TLV refers. If zero, no specific peer message is being which the Status TLV refers. If zero, no specific peer message is
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 Note that use of the Status TLV is not limited to Notification
messages. A message other than a Notification message may carry a messages. A message other than a Notification message may carry a
Status TLV as an Optional Parameter. When a message other than a Status TLV as an Optional Parameter. When a message other than a
Notification 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 TLV be set to 1 to indicate that the receiver should silently discard the
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 48, line 24 skipping to change at page 46, 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 response to this message. An LSR sending a notification message in
to this message should include this Message Id in the Status TLV response to this message should include this Message Id in the
carried by the notification message; see Section "Notification Status TLV carried by the notification message; see Section
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 parameters For messages that have required parameters, the required
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 parameters For messages that have optional parameters, the optional
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. LDP message.
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"
Hello "Hello Message" Hello "Hello Message"
Initialization "Initialization Message" Initialization "Initialization Message"
KeepAlive "KeepAlive Message" KeepAlive "KeepAlive Message"
Address "Address Message" Address "Address Message"
Address Withdraw "Address Withdraw Message" Address Withdraw "Address Withdraw Message"
Label Mapping "Label Mapping Message" Label Mapping "Label Mapping Message"
Label Request "Label Request Message" Label Request "Label Request Message"
Label Abort Request "Label Abort Request Message" Label Abort Request "Label Abort Request Message"
Label Withdraw "Label Withdraw Message" Label Withdraw "Label Withdraw Message"
Label Release "Label Release Message" Label Release "Label Release Message"
The sections that follow specify the encodings and procedures for The sections that follow specify the encodings and procedures for
these messages. these messages.
Some of the above messages are related to one another, for example Some of the above messages are related to one another, for example
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
skipping to change at page 50, line 27 skipping to change at page 47, line 51
|0| Notification (0x0001) | Message Length | |0| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) | | Status (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.
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 The 4 octet value is an Extended Status Code that encodes
additional information that supplements the status information additional information that supplements the status information
contained 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 that sent it. The value of this TLV is the PDU header and LSR that sent it. The value of this TLV is the PDU header and
as much PDU data following the header as appropriate for the as much PDU data following the header as appropriate for the
condition being signaled by the Notification message. condition 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 LSR that sent it. The value of this TLV is the message the LSR that sent it. The value of this TLV is the message
type and length fields and as much message data following the type and length fields and as much message data following the
type and length fields as appropriate for the condition being type and length fields as appropriate for the condition being
signaled by the Notification message. signaled by 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 advisory or error information it sends the peer a Notification
skipping to change at page 52, line 8 skipping to change at page 49, line 27
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 An LDP PDU received on a TCP connection for an LDP session is
malformed if: malformed if:
- The LDP Identifier in the PDU header is unknown to the receiver, - The LDP Identifier in the PDU header is unknown to the
or it is known but is not the LDP Identifier associated by the receiver, or it is known but is not the LDP Identifier
receiver with the LDP peer for this LDP session. This is a fatal associated by the receiver with the LDP peer for this LDP
error signaled by the Bad LDP Identifier Status Code. session. This is a fatal error signaled by the Bad LDP
Identifier Status Code.
- The LDP protocol version is not supported by the receiver, or it - The LDP protocol version is not supported by the receiver, or
is supported but is not the version negotiated for the session it is supported but is not the version negotiated for the
during session establishment. This is a fatal error signaled by session during session establishment. This is a fatal error
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 PDU Length Status Code. Section "Initialization Message" Bad PDU Length Status Code. Section "Initialization Message"
describes how the maximum PDU length for a session is determined. describes how the maximum PDU length for a session is
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 Code. is a fatal error signaled by the Bad Message Length Status
Code.
- The message is missing one or more Mandatory Parameters. This is - The message is missing one or more Mandatory Parameters. This
a non-fatal error signalled by the Missing Message Parameters is a non-fatal error signalled by the Missing Message
Status Code. Parameters 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 error
signaled by the Unknown TLV Status Code. 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. Section "Unknown TLV in Known Message Type" silently dropped. Section "Unknown TLV in Known Message Type"
elaborates on this behavior. elaborates on this behavior.
- The TLV Value is malformed. This occurs when the receiver - The TLV Value is malformed. This occurs when the receiver
handles the TLV but cannot decode the TLV Value. This is handles the TLV but cannot decode the TLV Value. This is
interpreted as indicative of a bug in either the sending or interpreted as indicative of a bug in either the sending or
receiving 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
skipping to change at page 54, line 40 skipping to change at page 52, line 18
|0| Hello (0x0100) | Message Length | |0| Hello (0x0100) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Hello Parameters TLV | | Common Hello Parameters 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.
Common Hello Parameters TLV Common Hello Parameters TLV
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 Hellos Hello hold time in seconds. An LSR maintains a record of
received from potential peers (see Section "Hello Message Hellos received from potential peers (see Section "Hello
Procedures"). Hello Hold Time specifies the time the sending LSR Message Procedures"). Hello Hold Time specifies the time the
will maintain its record of Hellos from the receiving LSR without sending LSR will maintain its record of Hellos from the
receipt of another Hello. receiving LSR without receipt of another Hello.
A pair of LSRs negotiates the hold times they use for Hellos from A pair of LSRs negotiates the hold times they use for Hellos
each other. Each proposes a hold time. The hold time used is from each other. Each proposes a hold time. The hold time
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 Link A value of 0 means use the default, which is 15 seconds for
Hellos and 45 seconds for Targeted Hellos. A value of 0xffff Link Hellos and 45 seconds for Targeted Hellos. A value of
means infinite. 0xffff means infinite.
T, Targeted Hello T, Targeted Hello
A value of 1 specifies that this Hello is a Targeted Hello. A A value of 1 specifies that this Hello is a Targeted Hello. A
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, the An LSR initiating Extended Discovery sets R to 1. If R is 1,
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 this request. If not, it ignores the request. If so, it
initiates 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 contains 0 or more parameters, each
encoded as a TLV. The optional parameters defined by this encoded as a TLV. The optional parameters defined by this
version of the protocol are version of the protocol are
Optional Parameter Type Length Value
IPv4 Transport Address 0x0401 4 See below Optional Parameter Type Length Value
Configuration 0x0402 4 See below
Sequence Number
IPv6 Transport Address 0x0403 16 See below
IPv4 Transport Address IPv4 Transport Address 0x0401 4 See below
Configuration 0x0402 4 See below
Sequence Number
IPv6 Transport Address 0x0403 16 See below
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 is not present the IPv4 source address for the UDP packet
carrying 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 the receiving LSR to detect configuration changes on the
sending 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 is not present the IPv6 source address for the UDP packet
carrying 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
skipping to change at page 57, line 8 skipping to change at page 54, line 26
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 for determining whether a Hello is acceptable are
implementation 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 Hello, it follows the procedures of Section "LDP Session
Establishment". 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
- 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 the sending LSR to signal configuration changes to the
receiving LSR. When a receiving LSR playing the active role in receiving LSR. When a receiving LSR playing the active role in
LDP session establishment detects a change in the sending LSR LDP session establishment detects a change in the sending LSR
configuration, 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 any, associated with the sending LSR (see Section "Session
Initialization"). 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
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|0| Initialization (0x0200) | Message Length | |0| Initialization (0x0200) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Session Parameters TLV | | Common Session Parameters 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.
Common Session Parameters TLV Common Session Parameters TLV
Specifies values proposed by the sending LSR for parameters that Specifies values proposed by the sending LSR for parameters that
must be negotiated for every LDP session. must be negotiated for every LDP session.
The encoding for the Common Session Parameters TLV is: The encoding for the Common Session 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 Sess Parms (0x0500)| Length | |0|0| Common Sess Parms (0x0500)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Version | KeepAlive Time | | Protocol Version | KeepAlive Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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 protocol. This version of the specification specifies LDP
protocol 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 Downstream Unsolicited advertisement; a value of 1 means
Downstream On Demand. Downstream On Demand.
If one LSR proposes Downstream Unsolicited and the other If one LSR proposes Downstream Unsolicited and the other
proposes Downstream on Demand, the rules for resolving this proposes Downstream on Demand, the rules for resolving this
difference 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 label-controlled Frame Relay link, then Downstream on Demand
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 is
unacceptable to an LSR, it must send a Session unacceptable to an LSR, it must send a Session
Rejected/Parameters Advertisement Mode Notification message in Rejected/Parameters Advertisement Mode Notification message in
response to the Initialization message and not establish the response to the Initialization message and not establish the
session. 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 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 detection is disabled (D = 0). If the loop detection
procedures would require the LSR to send a path vector that procedures would require the LSR to send a path vector that
exceeds this limit, the LSR will behave as if a loop had been exceeds this limit, the LSR will behave as if a loop had been
detected 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 of a peer's path vector limit will not change an LSR's
behavior, it does enable the LSR to alert an operator to a behavior, it does enable the LSR to alert an operator to a
possible 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.
The receiving LSR MUST calculate the maximum PDU length for the The receiving LSR MUST calculate the maximum PDU length for the
session by using the smaller of its and its peer's proposals session by using the smaller of its and its peer's proposals
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 one of its Hello adjacencies; see Section "Hello Message
Procedures". 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
ATM Session Parameters 0x0501 var See below ATM Session Parameters 0x0501 var See below
Frame Relay Session 0x0502 var See below Frame Relay Session 0x0502 var See below
Parameters Parameters
ATM Session Parameters ATM Session Parameters
Used when an LDP session manages label exchange for an ATM link Used when an LDP session manages label exchange for an ATM link
to specify ATM-specific session parameters. to specify ATM-specific session parameters.
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 Sess Parms (0x0501) | Length | |0|0| ATM Sess Parms (0x0501) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M | N |D| Reserved | | M | N |D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ATM Label Range Component 1 | | ATM Label Range Component 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ATM Label Range Component N | | ATM Label Range Component N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M, ATM Merge Capabilities M, ATM Merge Capabilities
Specifies the merge capabilities of an ATM switch. The Specifies the merge capabilities of an ATM switch. The
following values are supported in this version of the following values are supported in this version of the
specification: specification:
Value Meaning Value Meaning
0 Merge not supported 0 Merge not supported
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 - The interoperability of VP-merge-capable switches with non-
non-VP-merge-capable switches is a subject for future VP-merge-capable switches is a subject for future study.
study. When the LSRs differ on the use of VP-merge, the When the LSRs differ on the use of VP-merge, the session is
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 (see [ATM-VP]). LSR domain (see [ATM-VP]).
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 VPI) a given VCI may appear in a label mapping for one
direction on the link only. When either or both of the peers direction on the link only. When either or both of the peers
specifies unidirectional VC capability, both LSRs use specifies unidirectional VC capability, both LSRs use
unidirectional VC label assignment for the link as follows. unidirectional VC label assignment for the link as follows.
The LSRs compare their LDP Identifiers as unsigned integers. The LSRs compare their LDP Identifiers as unsigned integers.
The LSR with the larger LDP Identifier may assign only odd- The LSR with the larger LDP Identifier may assign only odd-
numbered VCIs in the VPI/VCI range as labels. The system with numbered VCIs in the VPI/VCI range as labels. The system with
the smaller LDP Identifier may assign only even-numbered VCIs the smaller LDP Identifier may assign only even-numbered VCIs
in the VPI/VCI range 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 which 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 received range and its own supported label range. The
intersection is the range in which the LSR may allocate and intersection is the range in which the LSR may allocate and
accept labels. LSRs MUST NOT establish a session with accept labels. LSRs MUST NOT establish a session with
neighbors for which the intersection of ranges is NULL. In neighbors for which the intersection of ranges is NULL. In
this case, the LSR must send a Session Rejected/Parameters this case, the LSR must send a Session Rejected/Parameters
Label Range Notification message in response to the Label Range Notification message in response to the
Initialization message and 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 This field is reserved. It must be set to zero on
transmission 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 originating Virtual Path Identifiers that is supported on the
switch. If the VPI is less than 12-bits it should be right originating switch. If the VPI is less than 12-bits it
justified in this field and preceding bits should be set to should be right justified in this field and preceding bits
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 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.
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 originating Virtual Path Identifiers that is supported on the
switch. If the VPI is less than 12-bits it should be right originating switch. If the VPI is less than 12-bits it
justified in this field and preceding bits should be set to should be right justified in this field and preceding bits
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, When peer LSRs are connected indirectly by means of an ATM VP, the
the sending LSR should set the Minimum and Maximum VPI fields to sending LSR should set the Minimum and Maximum VPI fields to 0,
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.
See [ATM-VP] for specification of the fields for ATM Label Range See [ATM-VP] for specification of the fields for ATM Label Range
Components to be used with VP merge LSRs. Components to be used with VP merge LSRs.
Frame Relay Session Parameters Frame Relay Session Parameters
Used when an LDP session manages label exchange for a Frame Relay Used when an LDP session manages label exchange for a Frame
link to specify Frame Relay-specific session parameters. Relay link to specify Frame Relay-specific session parameters.
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| FR Sess Parms (0x0502) | Length | |0|0| FR Sess Parms (0x0502) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M | N |D| Reserved | | M | N |D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Relay Label Range Component 1 | | Frame Relay Label Range Component 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 following values are supported in this version of the
specification: 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 N, Number of label range components
Specifies the number of Frame Relay Label Range Components Specifies the number of Frame Relay Label Range Components
included in the TLV. 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 link directions independently. A value of 1 specifies
unidirectional VC capability, meaning a given DLCI may appear unidirectional VC capability, meaning a given DLCI may appear
in a label mapping for one direction on the link only. When in a label mapping for one direction on the link only. When
either or both of the peers specifies unidirectional VC either or both of the peers specifies unidirectional VC
capability, both LSRs use unidirectional VC label assignment capability, both LSRs use unidirectional VC label assignment
for the link as follows. The LSRs compare their LDP for the link as follows. The LSRs compare their LDP
Identifiers as unsigned integers. The LSR with the larger LDP Identifiers as unsigned integers. The LSR with the larger LDP
Identifier may assign only odd-numbered DLCIs in the range as Identifier may assign only odd-numbered DLCIs in the range as
labels. The system with the smaller LDP Identifier may assign labels. The system with the smaller LDP Identifier may assign
only even-numbered 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 which 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 received range and its own supported label range. The
intersection is the range in which the LSR may allocate and intersection is the range in which the LSR may allocate and
accept labels. LSRs MUST NOT establish a session with accept labels. LSRs MUST NOT establish a session with
neighbors for which the intersection of ranges is NULL. In neighbors for which the intersection of ranges is NULL. In
this case, the LSR must send a Session Rejected/Parameters this case, the LSR must send a Session Rejected/Parameters
Label Range Notification message in response to the Label Range Notification message in response to the
Initialization message and 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 This field is reserved. It must be set to zero on
transmission and ignored on receipt. transmission 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 Link Connection Identifiers (DLCIs) that is supported on Data Link Connection Identifiers (DLCIs) that is supported
the originating switch. The DLCI should be right justified on the originating switch. The DLCI should be right
in this field and unused bits should be set to 0. justified in this 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 Link Connection Identifiers (DLCIs) that is supported on Data Link Connection Identifiers (DLCIs) that is supported
the originating switch. The DLCI should be right justified on the originating switch. The DLCI should be right
in this field and unused bits should be set to 0. justified in this 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. which 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 "Session Initialization" for general procedures for handling the
Initialization Message. Initialization Message.
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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
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| 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 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 Section LSR. The encoding for the Address List TLV is specified in Section
"Address List TLV". "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 message uses the addresses it
learns to maintain a database for mapping between peer LDP learns to maintain a database for mapping between peer LDP
Identifiers and next hop addresses; see Section "LDP Identifiers and Identifiers and next hop addresses; see Section "LDP Identifiers and
Next Hop Addresses". Next Hop Addresses".
When a new LDP session is initialized and before sending Label When a new LDP session is initialized and before sending Label
Mapping or Label Request messages an LSR should advertise its Mapping or Label Request messages an LSR should advertise its
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| 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 LSR. The list of interface addresses being withdrawn by the sending
The encoding for the Address list TLV is specified in Section LSR. The encoding for the Address list TLV is specified in
"Address List TLV". Section "Address List TLV".
Optional Parameters Optional Parameters
No optional parameters are defined for the Address Withdraw No optional parameters are defined for the Address Withdraw
message. 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 An LSR sends a Label Mapping message to an LDP peer to advertise
FEC-label bindings to the peer. FEC-label bindings to the peer.
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| 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 Specifies the FEC component of the FEC-Label mapping being
advertised. See Section "FEC TLV" for encoding. advertised. See Section "FEC TLV" for encoding.
Label TLV Label TLV
Specifies the Label component of the FEC-Label mapping. See Specifies the Label component of the FEC-Label mapping. See
Section "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 message it must include the Request Message Id optional
parameter. The value of this optional parameter is the Message parameter. The value of this optional parameter is the Message
Id of 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 LSP being setup by the Label Message. Section "Hop Count
Procedures" 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 Specifies the LSRs along the LSP being setup by the Label
Message. Section "Path Vector Procedures" describes how to Message. Section "Path Vector Procedures" describes how to
handle 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
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|0| Label Request (0x0401) | Message Length | |0| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC 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
The FEC for which a label is being requested. See Section "FEC The FEC for which a label is being requested. See Section "FEC
TLV" for encoding. 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
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 setup by the Label Request Message. Section "Hop
Count Procedures" describes how to handle this TLV. Count 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 setup by the Label
Request Message. Section "Path Vector Procedures" describes Request Message. Section "Path Vector Procedures" describes
how to handle this TLV. how to handle 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 An LSR may transmit a Request message under any of the following
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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 which
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 Resources until it receives a Notification message with the Label
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:
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| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Request Message ID TLV | | Label Request Message ID 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
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 message. No optional parameters are defined for the Label Abort Req
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 An LSR Ru may send a Label Abort Request message to abort an
outstanding Label Request message for FEC sent to LSR Rd in the outstanding Label Request message for FEC sent to LSR Rd in the
following 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 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
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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 message - A Label Mapping message in response to the Label Request
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 period elapses with no reply from the peer the LSR may reuse the
Message Id of the Label Request message; if it does so, it should Message Id of the Label Request message; if it does so, it should
also discard any record of the outstanding Label Request and Label also discard any record of the outstanding Label Request and Label
Abort 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
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| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 Identifies the FEC for which the FEC-label mapping is being
withdrawn. 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 An LSR transmits a Label Withdraw message under the following
conditions: 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.
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| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 Identifies the FEC for which the FEC-label mapping is being
released. released.
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 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 is no
longer needs a label previously received from or requested of that longer needs a label previously received from or requested of that
peer. peer.
An LSR must transmit a Label Release message under any of the An LSR must transmit a Label Release message under any of the
following conditions: following conditions:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 and (=0), a notification must be returned to the message originator
the entire message must be ignored; if U is set (=1), the unknown and the entire message must be ignored; if U is set (=1), the
TLV is silently ignored and the rest of the message is processed as unknown TLV is silently ignored and the rest of the message is
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 The determination as to whether a vendor-private message is
understood is based on the Type and the mandatory Vendor ID field. understood is based on the Type and the mandatory Vendor ID field.
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 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 and Vendor Id field specify how the Data field is to be
interpreted. interpreted.
Length Length
Specifies the cumulative length in octets of the Vendor ID and Data Specifies the cumulative length in octets of the Vendor ID and
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 |
skipping to change at page 83, line 27 skipping to change at page 80, line 32
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| 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 The determination as to whether a vendor-private message is
understood is based on the Msg Type and the Vendor ID parameter. understood is based on the Msg Type and the Vendor ID parameter.
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, Vendor Specifies the cumulative length in octets of the Message ID,
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 response to this message. An LSR sending a notification message in
to this message will include this Message Id in the notification response to this message will include this Message Id in the
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 experimental - The Type range 0x3F00 through 0x3FFF is reserved for
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 with place of a Vendor ID field. The Experiment ID field is used
the Type or Message Type field to specify the interpretation of with the Type or Message Type field to specify the
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
Notification 0x0001 "Notification Message" Notification 0x0001 "Notification Message"
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
FEC 0x0100 "FEC TLV"
Address List 0x0101 "Address List TLV"
Hop Count 0x0103 "Hop Count TLV"
Path Vector 0x0104 "Path Vector TLV"
Generic Label 0x0200 "Generic Label TLV"
ATM Label 0x0201 "ATM Label TLV"
Frame Relay Label 0x0202 "Frame Relay Label TLV"
Status 0x0300 "Status TLV"
Extended Status 0x0301 "Notification Message"
Returned PDU 0x0302 "Notification Message"
Returned Message 0x0303 "Notification Message"
Common Hello 0x0400 "Hello Message"
Parameters
IPv4 Transport Address 0x0401 "Hello Message"
Configuration 0x0402 "Hello Message"
Sequence Number
IPv6 Transport Address 0x0403 "Hello Message"
Common Session 0x0500 "Initialization Message"
Parameters
ATM Session Parameters 0x0501 "Initialization Message"
Frame Relay Session 0x0502 "Initialization Message"
Parameters
Label Request 0x0600 "Label Mapping Message" FEC 0x0100 "FEC TLV"
Message ID Address List 0x0101 "Address List TLV"
Vendor-Private 0x3E00- "LDP Vendor-private Extensions" Hop Count 0x0103 "Hop Count TLV"
0x3EFF Path Vector 0x0104 "Path Vector TLV"
Experimental 0x3F00- "LDP Experimental Extensions" Generic Label 0x0200 "Generic Label TLV"
0x3FFF ATM Label 0x0201 "ATM Label TLV"
Frame Relay Label 0x0202 "Frame Relay Label TLV"
Status 0x0300 "Status TLV"
Extended Status 0x0301 "Notification Message"
Returned PDU 0x0302 "Notification Message"
Returned Message 0x0303 "Notification Message"
Common Hello 0x0400 "Hello Message"
Parameters
IPv4 Transport Address 0x0401 "Hello Message"
Configuration 0x0402 "Hello Message"
Sequence Number
IPv6 Transport Address 0x0403 "Hello Message"
Common Session 0x0500 "Initialization Message"
Parameters
ATM Session Parameters 0x0501 "Initialization Message"
Frame Relay Session 0x0502 "Initialization Message"
Parameters
Label Request 0x0600 "Label Mapping Message"
Message ID
Vendor-Private 0x3E00- "LDP Vendor-private Extensions"
0x3EFF
Experimental 0x3F00- "LDP Experimental Extensions"
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
"Status Data" column is the value of the 30-bit Status Data field in "Status Data" column is the value of the 30-bit Status Data field in
the Status Code TLV. the Status Code TLV.
Note that the setting of the Status Code F-bit is at the discretion Note that the setting of the Status Code F-bit is at the discretion
of the LSR originating the Status TLV. of the LSR originating the Status TLV.
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 ..."
Expired
Label Request Aborted 0 0x00000015 "Label Request Abort ..."
Missing Message 0 0x00000016 "Events Signaled by ..."
Parameters
Unsupported Address 0 0x00000017 "FEC Procedures"
Family "Address Message Proc ..."
KeepAlive Timer 1 0x00000014 "Events Signaled by ..." Session Rejected/ 1 0x00000018 "Session Initialization"
Expired Bad KeepAlive Time
Label Request Aborted 0 0x00000015 "Label Request Abort ..." Internal Error 1 0x00000019 "Events Signaled by ..."
Missing Message 0 0x00000016 "Events Signaled by ..."
Parameters
Unsupported Address 0 0x00000017 "FEC Procedures"
Family "Address Message Proc ..."
Session Rejected/ 1 0x00000018 "Session Initialization"
Bad KeepAlive Time
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 (see [ARCH]) is represented as a Generic The Implicit NULL label (see [RFC3031]) is represented as a Generic
Label TLV with a Label field value as specified by [ENCAP]. Label TLV with a Label field value as specified by [RFC3032].
4. IANA Considerations 4. IANA Considerations
LDP defines the following name spaces which require management: LDP defines the following name spaces which 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 responsibility reserved for Vendor Private extensions and are the
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 of Extensions" and "Experiment ID Name Space"). IANA management
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 Experiment however, IANA is responsible for managing part of the
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 LDP divides the name space for TLV types into three ranges. The
following 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 reserved - TLV Types 0x3E00 - 0x3EFF. TLV types in this range are
for Vendor Private extensions and are the responsibility of the reserved for Vendor Private extensions and are the
individual vendors (see Section "LDP Vendor-private TLVs"). IANA responsibility of the individual vendors (see Section "LDP
management of this range of the TLV Type Name Space is Vendor-private TLVs"). IANA management of this range of the
unnecessary. TLV Type Name Space is unnecessary.
- TLV Types 0x3F00 - 0x3FFF. TLV types in this range are reserved - TLV Types 0x3F00 - 0x3FFF. TLV types in this range are
for Experimental extensions and are the responsibility of the reserved for Experimental extensions and are the responsibility
individual experimenters (see Sections "LDP Experimental of the individual experimenters (see Sections "LDP Experimental
Extensions" and "Experiment ID Name Space"). IANA management of Extensions" and "Experiment ID Name Space"). IANA management
this range of the TLV Name Space is unnecessary; however, IANA is of this range of the TLV Name Space is unnecessary; however,
responsible for managing part of the Experiment ID Name Space IANA is responsible for managing part of the Experiment ID Name
(see below). Space (see below).
4.3. FEC Type Name Space 4.3. FEC Type Name Space
The range for FEC types is 0 - 255. The range for FEC types is 0 - 255.
Following the policies outlined in [IANA], FEC types in the range 0 - Following the policies outlined in [IANA], FEC types in the range 0 -
127 are allocated through an IETF Consensus action, types in the 127 are allocated through an IETF Consensus action, types in the
range 128 - 191 are allocated as First Come First Served, and types range 128 - 191 are allocated as First Come First Served, and types
in the range 192 - 255 are reserved for Private Use. in the range 192 - 255 are reserved for Private Use.
skipping to change at page 89, line 43 skipping to change at page 86, line 34
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 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 messages over the link. The threat of spoofed Basic Hellos can be
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 Hello messages to indicate willingness to establish an LDP
session. An LSR can reduce the threat of spoofed Extended Hellos session. An LSR can reduce the threat of spoofed Extended Hellos
by 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 some to be too weak for this application. It also points out that
that a similar TCP option with a stronger hashing algorithm (it a similar TCP option with a stronger hashing algorithm (it cites
cites SHA-1 as an example) could be deployed. To our knowledge SHA-1 as an example) could be deployed. To our knowledge no such
no such TCP option has been defined and deployed. However, we TCP option has been defined and deployed. However, we note that
note that LDP can use whatever TCP message digest techniques are LDP can use whatever TCP message digest techniques are available,
available, and when one stronger than MD5 is specified and and when one stronger than MD5 is specified and implemented,
implemented, upgrading LDP to use it would be relatively upgrading LDP to use it would be relatively straightforward.
straightforward.
5.2. Privacy 5.2. Privacy
LDP provides no mechanism for protecting the privacy of label LDP provides no mechanism for protecting the privacy of label
distribution. distribution.
The security requirements of label distribution protocols are The security requirements of label distribution protocols are
essentially identical to those of the protocols which distribute essentially identical to those of the protocols which distribute
routing information. By providing a mechanism to ensure the routing information. By providing a mechanism to ensure the
authenticity and integrity of its messages LDP provides a level of authenticity and integrity of its messages LDP provides a level of
security which is at least as good as, though no better than, that security which is at least as good as, though no better than, that
which can be provided by the routing protocols themselves. The more which can be provided by the routing protocols themselves. The more
general issue of whether privacy should be required for routing general issue of whether privacy should be required for routing
protocols is beyond 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 the threat of label spoofing. However, that privacy would not
protect against label spoofing attacks since data packets carry protect against label spoofing attacks since data packets carry
labels in the clear. Furthermoe, label spoofing attacks can be made labels in the clear. Furthermore, label spoofing attacks can be made
without 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 adminstrator 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 which can be trusted to not initiate such an attack.
Interfaces to peers interior to the administrator's domain should
not represent a threat since interior peers are under the
administrator's control. Interfaces to peers exterior to the
domain represent a potential threat since exterior peers are not.
An adminstrator can reduce that threat by connecting the LSR only
to exterior peers that can be trusted to not initiate a Basic
Hello attack.
DoS attacks via Extended Hellos are potentially a more serious Interfaces to peers interior to the administrator's domain should
threat. This threat can be addressed by filtering Extended not represent a threat since interior peers are under the
Hellos using access lists that define addresses with which administrator's control. Interfaces to peers exterior to the
extended discovery is permitted. However, performing the domain represent a potential threat since exterior peers are not.
filering requires LSR resource. An administrator can reduce that threat by connecting the LSR only
to exterior peers that can be trusted to not initiate a Basic
Hello attack.
In an environment where a trusted MPLS cloud can be identified, DoS attacks via Extended Hellos are potentially a more serious
LSRs at the edge of the cloud can be used to protect interior threat. This threat can be addressed by filtering Extended Hellos
LSRs against DoS attacks via Extended Hellos by filtering out using access lists that define addresses with which extended
Extended Hellos originating outside of the trusted MPLS cloud, discovery is permitted. However, performing the filtering
accepting only those originating at addresses permitted by access requires LSR resource.
lists. This filtering protects LSRs in the interior of the cloud
but consumes resoures at the edges.
2. Well known TCP port for LDP Session Establishment 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
against DoS attacks via Extended Hellos by filtering out Extended
Hellos originating outside of the trusted MPLS cloud, accepting
only those originating at addresses permitted by access lists.
This filtering protects LSRs in the interior of the cloud but
consumes resources at the edges.
Like other control plane protocols that use TCP, LDP may be the 2. Well known TCP port for LDP Session Establishment
target of DoS attacks, such a SYN attacks. LDP is no more or
less vulnerable to such attacks than other control plane
protocols that use TCP.
The threat of such attacks can be mitigated somewhat by the Like other control plane protocols that use TCP, LDP may be the
following: target of DoS attacks, such a SYN attacks. LDP is no more or less
vulnerable to such attacks than other control plane protocols that
use TCP.
o An LSR should avoid promiscuous TCP listens for LDP session The threat of such attacks can be mitigated somewhat by the
establishment. It should use only listens that are specific following:
to discovered peers. This enables it to drop attack packets
early in their processing since they are less likely to match
existing or in-progress connections.
o The use of the MD5 option helps somewhat since it prevents a o An LSR should avoid promiscuous TCP listens for LDP session
SYN from being accepted unless the MD5 segment checksum is establishment. It should use only listens that are specific
valid. However, the receiver must compute the checksum to discovered peers. This enables it to drop attack packets
before it can decide to discard an otherwise acceptable SYN early in their processing since they are less likely to
segment. match existing or in-progress connections.
o The use of access list mechanisms applied at the boundary of o The use of the MD5 option helps somewhat since it prevents a
the MPLS cloud in a manner similar to that suggested above SYN from being accepted unless the MD5 segment checksum is
for Extended Hellos can protect the interior against attacks valid. However, the receiver must compute the checksum
originating from outside the cloud. before it can decide to discard an otherwise acceptable SYN
segment.
o The use of access list mechanisms applied at the boundary of
the MPLS cloud in a manner similar to that suggested above
for Extended Hellos can protect the interior against attacks
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 The following topics not addressed in this version of LDP are
possible areas for future study: possible areas for future study:
- Section 2.16 of the MPLS architecture [ARCH] requires that the - Section 2.16 of the MPLS architecture [RFC3031] requires that
initial label distribution protocol negotiation between peer LSRs the initial label distribution protocol negotiation between
enable each LSR to determine whether its peer is capable of peer LSRs enable each LSR to determine whether its peer is
popping the label stack. This version of LDP assumes that LSRs capable of popping the label stack. This version of LDP
support label popping for all link types except ATM and Frame assumes that LSRs support label popping for all link types
Relay. A future version may specify means to make this except ATM and Frame Relay. A future version may specify means
determination part of the session initiation negotiation. to make this determination part of the session initiation
negotiation.
- LDP support for CoS is not specified in this version. CoS - LDP support for CoS is not specified in this version. CoS
support may be addressed in a future version. 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.
7. Intellectual Property Considerations 7. Intellectual Property Considerations
The IETF has been notified of intellectual property rights claimed in The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this regard to some or all of the specification contained in this
document. For more information consult the online list of claimed document. For more information consult the online list of claimed
rights. rights.
8. Acknowledgments 8. Acknowledgments
The ideas and text in this document have been collected from a number The ideas and text in this document have been collected from a number
of sources. We would like to thank Rick Boivie, Ross Callon, Alex of 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. Rekhter, and Arun Viswanathan.
9. References 9. References
[ARCH] E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label [ATM-VP] N. Feldman, B. Jamoussi, S. Komandur, A, Viswanathan, T
Switching Architecture", Work in Progress, July 1998. Worster, "MPLS using ATM VP Switching", Work in Progress.
[ATM] B. Davie, J. Lawrence, K. McCloghrie, Y. Rekhter, E. Rosen, G. [CRLDP] L. Andersson, A. Fredette, B. Jamoussi, R. Callon, P.
Swallow, P. Doolan, "Use of Label Switching With ATM", Work in Doolan, N. Feldman, E. Gray, J. Halpern, J. Heinanen T.
Progress, September, 1998. E. Kilty, A. G. Malis, M. Girish, K. Sundell, P.
Vaananen, T. Worster, L. Wu, R. Dantu, "Constraint-Based
LSP Setup using LDP", Work in Progress.
[ATM-VP] N. Feldman, B. Jamoussi, S. Komandur, A, Viswanathan, T [DIFFSERV] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
Worster, "MPLS using ATM VP Switching", Work in Progress, February, and W. Weiss, "An Architecture for Differentiated
1999. Services", RFC 2475, December 1998.
[CRLDP] L. Andersson, A. Fredette, B. Jamoussi, R. Callon, P. Doolan, [IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing an
N. Feldman, E. Gray, J. Halpern, J. Heinanen T. E. Kilty, A. G. IANA Considerations Section in RFCs", BCP 26, RFC 2434,
Malis, M. Girish, K. Sundell, P. Vaananen, T. Worster, L. Wu, R. October 1998.
Dantu, "Constraint-Based LSP Setup using LDP", Work in Progress,
January, 1999.
[DIFFSERV] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC 1321,
Weiss, "An Architecture for Differentiated Services", Work in April 1992.
Progress, October, 1998.
[ENCAP] E. Rosen, Y. Rekhter, D. Tappan, D. Farinacci, G. Fedorkow, [RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM
T. Li, A. Conta, "MPLS Label Stack Encoding", Work in Progress, July, Adaptation Layer 5", RFC 1483, July 1993.
1998.
[FR] A. Conta, P. Doolan, A. Malis, "Use of Label Switching on Frame [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
Relay Networks", Work in Progress, October, 1998.
[IANA] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA [RFC1700] Reynolds, J. and J. Postel, "ASSIGNED NUMBERS", STD 2,
Considerations Section in RFCs", RFC 2434, October 1998. RFC 1700, October 1994.
[LDPAPPLIC] B. Thomas, E. Gray, "LDP Applicability", Work in [RFC1771] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
Progress, June 2000. (BGP-4)", RFC 1771, March 1995.
[LSPTUN] D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow, Vijay [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Srinivasan, "Extensions to RSVP for LSP Tunnels", Work in Progress, Requirement Levels", BCP 14, RFC 2119, March 1997.
November 1998.
[rfc1321] R. Rivest, "The MD5 Message-Digest Algorithm," RFC 1321, [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
April 1992. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[rfc1483] J. Heinanen, "Multiprotocol Encapsulation over ATM [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP
Adaptation Layer 5", RFC 1483, Telecom Finland, July 1993. MD5 Signature Option", RFC 2385, August 1998.
[rfc1583] J. Moy, "OSPF Version 2", RFC 1583, Proteon Inc, March [RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J.
1994. McManus, "Requirements for Traffic Engineering over
MPLS", RFC 2702, September 1999.
[rfc1700] J. Reynolds, J.Postel, "ASSIGNED NUMBERS", October 1994. [RFC3031] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[rfc1771] Y. Rekhter, T. Li, "A Border Gateway Protocol 4 (BGP-4)", [RFC3032] Rosen, E., Rekhter, Y., Tappan, D., Farinacci, D.,
RFC 1771, March 1995. Fedorkow, G., Li, T. and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
[rfc2119] S. Bradner, "Key words for use in RFCs to Indicate [RFC3034] Conta, A., Doolan, P. and A. Malis, "Use of Label
Requirement Levels", RFC 2119, March 1997. Switching on Frame Relay Networks Specification", RFC
3034, January 2001.
[rfc2205] R. Braden, L. Zhang, S. Berson, S. Herzog, S. Jamin, [RFC3035] Davie, B., Lawrence, J., McCloghrie, K., Rekhter, Y.,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Rosen, E., Swallow, G. and P. Doolan, "MPLS using LDP and
Specification", RFC 2205, September 1997. ATM VC Switching", RFC 3035, January 2001.
[rfc2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 [RFC3037] Thomas, B. and E. Gray, "LDP Applicability", RFC 3037,
Signature Option", RFC 2385, August 1998. January 2001.
[TE] D. Awduche, J. Malcolm, J Agogbua, M. O'Dell, J. McManus, " 10. Authors' Addresses
Requirements for Traffic Engineering over MPLS", Work in Progress,
October 1998.
10. Author Information Loa Andersson
Nortel Networks Inc
St Eriksgatan 115, PO Box 6701
113 85 Stockholm
Sweden
Loa Andersson Andre Fredette Phone: +46 8 5088 36 34
Nortel Networks Inc PhotonEx Corporation
St Eriksgatan 115, PO Box 6701 8C Preston Court
113 85 Stockholm Bedford, MA 01730
Sweden Phone: 781-301-4655
Phone: +46 8 5088 36 34 email: fredette@photonex.com
Mobile: +46 70 522 78 34 Mobile: +46 70 522 78 34
email: loa.andersson@nortelnetworks.com EMail: loa.andersson@nortelnetworks.com
Paul Doolan Bob Thomas Paul Doolan
Ennovate Networks Cisco Systems, Inc. Ennovate Networks
330 Codman Hill Rd 250 Apollo Dr. 60 Codman Hill Rd
Marlborough MA 01719 Chelmsford, MA 01824 Marlborough MA 01719
Phone: 978-263-2002 Phone: 978-244-8078
email: pdoolan@ennovatenetworks.com email: rhthomas@cisco.com Phone: 978-263-2002
EMail: pdoolan@ennovatenetworks.com
Nancy Feldman Nancy Feldman
IBM Corp. IBM Research
17 Skyline Drive 30 Saw Mill River Road
Hawthorne NY 10532 Hawthorne, NY 10532
Phone: 914-784-3254 Phone: 914-784-3254
email: nkf@us.ibm.com EMail: nkf@us.ibm.com
Andre Fredette
PhotonEx Corporation
8C Preston Court
Bedford, MA 01730
Phone: 781-301-4655
EMail: fredette@photonex.com
Bob Thomas
Cisco Systems, Inc.
250 Apollo Dr.
Chelmsford, MA 01824
Phone: 978-244-8078
EMail: rhthomas@cisco.com
Appendix A. LDP Label Distribution Procedures Appendix A. LDP Label Distribution Procedures
This section specifies label distribution behavior in terms of LSR This section specifies label distribution behavior in terms of LSR
response to the following events: response to the following events:
- Receive Label Request Message; - Receive Label Request Message;
- Receive Label Mapping Message; - Receive Label Mapping Message;
- Receive Label Abort Request Message; - Receive Label Abort Request Message;
- Receive Label Release Message; - Receive Label Release Message;
- Receive Label Withdraw Message; - Receive Label Withdraw Message;
- Recognize new FEC; - Recognize new FEC;
- Detect change in FEC next hop; - Detect change in FEC next hop;
- Receive Notification Message / Label Request Aborted; - Receive Notification Message / Label Request Aborted;
- Receive Notification Message / No Label Resources; - Receive Notification Message / No Label Resources;
- Receive Notification Message / No Route; - Receive Notification Message / No Route;
- Receive Notification Message / Loop Detected; - Receive Notification Message / Loop Detected;
- Receive Notification Message / Label Resources Available; - Receive Notification Message / Label Resources Available;
- Detect local label resources have become available; - Detect local label resources have become available;
- LSR decides to no longer label switch a FEC; - LSR decides to no longer label switch a FEC;
- Timeout of deferred label request. - Timeout of deferred label request.
The specification of LSR behavior in response to an event has three The specification of LSR behavior in response to an event has three
parts: parts:
1. Summary. Prose that describes LSR response to the event in 1. Summary. Prose that describes LSR response to the event in
overview. overview.
2. Context. A list of elements referred to by the Algorithm part 2. Context. A list of elements referred to by the Algorithm part
of the specification. (See 3.) of the specification. (See 3.)
3. Algorithm. An algorithm for LSR response to the event. 3. Algorithm. An algorithm for LSR response to the event.
The Summary may omit details of the LSR response, such as bookkeeping The Summary may omit details of the LSR response, such as bookkeeping
action or behavior dependent on the LSR label advertisement mode, action or behavior dependent on the LSR label advertisement mode,
control mode, or label retention mode in use. The intent is that the control mode, or label retention mode in use. The intent is that the
Algorithm fully and unambiguously specify the LSR response. Algorithm fully and unambiguously specify the LSR response.
The algorithms in this section use procedures defined in the MPLS The algorithms in this section use procedures defined in the MPLS
architecture specification [ARCH] for hop-by-hop routed traffic. architecture specification [RFC3031] for hop-by-hop routed traffic.
These procedures are: These procedures are:
- Label Distribution procedure, which is performed by a downstream - Label Distribution procedure, which is performed by a
LSR to determine when to distribute a label for a FEC to LDP downstream LSR to determine when to distribute a label for a
peers. The architecture defines four Label Distribution FEC to LDP peers. The architecture defines four Label
procedures: Distribution procedures:
. Downstream Unsolicited Independent Control, called . Downstream Unsolicited Independent Control, called
PushUnconditional in [ARCH]. PushUnconditional in [RFC3031].
. Downstream Unsolicited Ordered Control, called . Downstream Unsolicited Ordered Control, called
PushConditional in [ARCH]. PushConditional in [RFC3031].
. Downstream On Demand Independent Control, called . Downstream On Demand Independent Control, called
PulledUnconditional in [ARCH]. PulledUnconditional in [RFC3031].
. Downstream On Demand Ordered Control, called . Downstream On Demand Ordered Control, called
PulledConditional in [ARCH]. PulledConditional in [RFC3031].
- Label Withdrawal procedure, which is performed by a downstream - Label Withdrawal procedure, which is performed by a downstream
LSR to determine when to withdraw a FEC label mapping previously LSR to determine when to withdraw a FEC label mapping
distributed to LDP peers. The architecture defines a single Label previously distributed to LDP peers. The architecture defines
Withdrawal procedure. Whenever an LSR breaks the binding between a single Label Withdrawal procedure. Whenever an LSR breaks
a label and a FEC, it must withdraw the FEC label mapping from the binding between a label and a FEC, it must withdraw the FEC
all LDP peers to which it has previously sent the mapping. label mapping from all LDP peers to which it has previously
sent the mapping.
- Label Request procedure, which is performed by an upstream LSR to - Label Request procedure, which is performed by an upstream LSR
determine when to explicitly request that a downstream LSR bind a to determine when to explicitly request that a downstream LSR
label to a FEC and send it the corresponding label mapping. The bind a label to a FEC and send it the corresponding label
architecture defines three Label Request procedures: mapping. The architecture defines three Label Request
procedures:
. Request Never. The LSR never requests a label. . Request Never. The LSR never requests a label.
. Request When Needed. The LSR requests a label whenever it . Request When Needed. The LSR requests a label whenever
needs one. it needs one.
. Request On Request. This procedure is used by non-label . Request On Request. This procedure is used by
merging LSRs. The LSR requests a label when it receives a non-label merging LSRs. The LSR requests a label
request for one, in addition to whenever it needs one. when it receives a request for one, in addition
to whenever it needs one.
- Label Release procedure, which is performed by an upstream LSR to - Label Release procedure, which is performed by an upstream LSR
determine when to release a previously received label mapping for to determine when to release a previously received label
a FEC. The architecture defines two Label Release procedures: mapping for a FEC. The architecture defines two Label Release
procedures:
. Conservative label retention, called Release On Change in . Conservative label retention, called Release On Change in
[ARCH]. [RFC3031].
. Liberal label retention, called No Release On Change in . Liberal label retention, called No Release On Change in
[ARCH]. [RFC3031].
- Label Use procedure, which is performed by an LSR to determine - Label Use procedure, which is performed by an LSR to determine
when to start using a FEC label for forwarding/switching. The when to start using a FEC label for forwarding/switching. The
architecture defines three Label Use procedures: architecture defines three Label Use procedures:
. Use Immediate. The LSR immediately uses a label received from . Use Immediate. The LSR immediately uses a label received
a FEC next hop for forwarding/switching. from a FEC next hop for forwarding/switching.
. Use If Loop Free. The LSR uses a FEC label received from a . Use If Loop Free. The LSR uses a FEC label received from a
FEC next hop for forwarding/switching only if it has FEC next hop for forwarding/switching only if it has
determined that by doing so it will not cause a forwarding determined that by doing so it will not cause a forwarding
loop. loop.
. Use If Loop Not Detected. This procedure is the same as Use . Use If Loop Not Detected. This procedure is the same as Use
Immediate unless the LSR has detected a loop in the FEC LSP. Immediate unless the LSR has detected a loop in the FEC LSP.
Use of the FEC label for forwarding/switching will continue Use of the FEC label for forwarding/switching will continue
until the next hop for the FEC changes or the loop is no until the next hop for the FEC changes or the loop is no
longer detected. longer detected.
This version of LDP does not include a loop prevention mechanism; This version of LDP does not include a loop prevention
therefore, the procedures below do not make use of the Use If mechanism; therefore, the procedures below do not make use of
Loop Free procedure. the Use If Loop Free procedure.
- Label No Route procedure (called Label Not Available procedure in - Label No Route procedure (called Label Not Available procedure
[ARCH]), which is performed by an upstream LSR to determine how in [RFC3031]), which is performed by an upstream LSR to
to respond to a No Route notification from a downstream LSR in determine how to respond to a No Route notification from a
response to a request for a FEC label mapping. The architecture downstream LSR in response to a request for a FEC label
specification defines two Label No Route procedures: mapping. The architecture specification defines two Label No
Route procedures:
. Request Retry. The LSR should issue the label request at a . Request Retry. The LSR should issue the label request at a
later time. later time.
. No Request Retry. The LSR should assume the downstream LSR . No Request Retry. The LSR should assume the downstream LSR
will provide a label mapping when the downstream LSR has a will provide a label mapping when the downstream LSR has a
next hop and it should not reissue the request. next hop and it should not reissue the request.
A.1. Handling Label Distribution Events A.1. Handling Label Distribution Events
This section defines LDP label distribution procedures by specifying This section defines LDP label distribution procedures by specifying
an algorithm for each label distribution event. The requirement on an algorithm for each label distribution event. The requirement on
an LDP implementation is that its event handling must have the effect an LDP implementation is that its event handling must have the effect
specified by the algorithms. That is, an implementation need not specified by the algorithms. That is, an implementation need not
follow exactly the steps specified by the algorithms as long as the follow exactly the steps specified by the algorithms as long as the
effect is identical. effect is identical.
skipping to change at page 99, line 11 skipping to change at page 96, line 19
follows this. follows this.
An implementation would use data structures to store information An implementation would use data structures to store information
about protocol activity. This appendix specifies the information to about protocol activity. This appendix specifies the information to
be stored in sufficient detail to describe the algorithms, and be stored in sufficient detail to describe the algorithms, and
assumes the ability to retrieve the information as needed. It does assumes the ability to retrieve the information as needed. It does
not specify the details of the data structures. not specify the details of the data structures.
A.1.1. Receive Label Request A.1.1. Receive Label Request
Summary: Summary:
The response by an LSR to receipt of a FEC label request from an
LDP peer may involve one or more of the following actions:
- Transmission of a notification message to the requesting LSR The response by an LSR to receipt of a FEC label request from an
indicating why a label mapping for the FEC cannot be provided; LDP peer may involve one or more of the following actions:
- Transmission of a FEC label mapping to the requesting LSR; - Transmission of a notification message to the requesting LSR
indicating why a label mapping for the FEC cannot be provided;
- Transmission of a FEC label request to the FEC next hop; - Transmission of a FEC label mapping to the requesting LSR;
- Installation of labels for forwarding/switching use by the LSR. - Transmission of a FEC label request to the FEC next hop;
Context: - Installation of labels for forwarding/switching use by the LSR.
- LSR. The LSR handling the event. Context:
- MsgSource. The LDP peer that sent the message. - LSR. The LSR handling the event.
- FEC. The FEC specified in the message. - MsgSource. The LDP peer that sent the message.
- RAttributes. Attributes received with the message. E.g., Hop - FEC. The FEC specified in the message.
Count Path Vector.
- SAttributes. Attributes to be included in Label Request message, - RAttributes. Attributes received with the message. E.g., Hop
if any, propagated to FEC Next Hop. Count, Path Vector.
- StoredHopCount. The hop count, if any, previously recorded for - SAttributes. Attributes to be included in Label Request
the FEC. message, if any, propagated to FEC Next Hop.
Algorithm: - StoredHopCount. The hop count, if any, previously recorded for
the FEC.
LRq.1 Execute procedure Check_Received_Attributes (MsgSource, Algorithm:
LabelRequest, RAttributes).
If Loop Detected, goto LRq.13.
LRq.2 Is there a Next Hop for FEC? LRq.1 Execute procedure Check_Received_Attributes (MsgSource,
If not, goto LRq.5. LabelRequest, RAttributes).
If Loop Detected, goto LRq.13.
LRq.3 Is MsgSource the Next Hop? LRq.2 Is there a Next Hop for FEC?
Ifnot, goto LRq.6. If not, goto LRq.5.
LRq.4 Execute procedure Send_Notification (MsgSource, Loop LRq.3 Is MsgSource the Next Hop?
Detected). Ifnot, goto LRq.6.
Goto LRq.13
LRq.5 Execute procedure Send_Notification (MsgSource, No Route). LRq.4 Execute procedure Send_Notification (MsgSource, Loop
Goto LRq.13. Detected).
Goto LRq.13
LRq.6 Has LSR previously received a label request for FEC from LRq.5 Execute procedure Send_Notification (MsgSource, No Route).
MsgSource? Goto LRq.13.
If not, goto LRq.8. (See Note 1.)
LRq.7 Is the label request a duplicate request? LRq.6 Has LSR previously received a label request for FEC from
If so, Goto LRq.13. (See Note 2.) MsgSource?
If not, goto LRq.8. (See Note 1.)
LRq.8 Record label request for FEC received from MsgSource and mark LRq.7 Is the label request a duplicate request?
it pending. If so, Goto LRq.13. (See Note 2.)
LRq.9 Perform LSR Label Distribution procedure: LRq.8 Record label request for FEC received from MsgSource and
mark it pending.
For Downstream Unsolicited Independent Control OR LRq.9 Perform LSR Label Distribution procedure:
For Downstream On Demand Independent Control
1. Has LSR previously received and retained a label For Downstream Unsolicited Independent Control OR
mapping for FEC from Next Hop?. For Downstream On Demand Independent Control
Is so, set Propagating to IsPropagating.
If not, set Propagating to NotPropagating.
2. Execute procedure 1. Has LSR previously received and retained a label
Prepare_Label_Mapping_Attributes(MsgSource, FEC, mapping for FEC from Next Hop?.
RAttributes, SAttributes, Propagating, Is so, set Propagating to IsPropagating.
StoredHopCount). If not, set Propagating to NotPropagating.
3. Execute procedure Send_Label (MsgSource, FEC, 2. Execute procedure
SAttributes). Prepare_Label_Mapping_Attributes(MsgSource, FEC,
RAttributes, SAttributes, Propagating,
StoredHopCount).
4. Is LSR egress for FEC? OR 3. Execute procedure Send_Label (MsgSource, FEC,
Has LSR previously received and retained a label SAttributes).
mapping for FEC from Next Hop?
If so, goto LRq.11. If not, goto LRq.10.
For Downstream Unsolicited Ordered Control OR 4. Is LSR egress for FEC? OR
For Downstream On Demand Ordered Control Has LSR previously received and retained a label
mapping for FEC from Next Hop?
If so, goto LRq.11.
If not, goto LRq.10.
1. Is LSR egress for FEC? OR For Downstream Unsolicited Ordered Control OR
Has LSR previously received and retained a label For Downstream On Demand Ordered Control
mapping for FEC from Next Hop? (See Note 3.)
If not, goto LRq.10.
2. Execute procedure 1. Is LSR egress for FEC? OR
Prepare_Label_Mapping_Attributes(MsgSource, FEC, Has LSR previously received and retained a label
RAttributes, SAttributes, IsPropagating, mapping for FEC from Next Hop? (See Note 3.)
StoredHopCount) If not, goto LRq.10.
3. Execute procedure Send_Label (MsgSource, FEC, 2. Execute procedure
SAttributes). Prepare_Label_Mapping_Attributes(MsgSource, FEC,
Goto LRq.11. RAttributes, SAttributes, IsPropagating,
StoredHopCount)
LRq.10 Perform LSR Label Request procedure: 3. Execute procedure Send_Label (MsgSource, FEC,
SAttributes).
Goto LRq.11.
For Request Never LRq.10 Perform LSR Label Request procedure:
1. Goto LRq.13. For Request Never
For Request When Needed OR 1. Goto LRq.13.
For Request On Request
1. Execute procedure Prepare_Label_Request_Attributes For Request When Needed OR
(Next Hop, FEC, RAttributes, SAttributes); For Request On Request
2. Execute procedure Send_Label_Request (Next Hop, FEC, 1. Execute procedure Prepare_Label_Request_Attributes
SAttributes). (Next Hop, FEC, RAttributes, SAttributes);
Goto LRq.13.
LRq.11 Has LSR successfully sent a label for FEC to MsgSource? 2. Execute procedure Send_Label_Request (Next Hop, FEC,
If not, goto LRq.13. (See Note 4.) SAttributes).
Goto LRq.13.
LRq.12 Perform LSR Label Use procedure. LRq.11 Has LSR successfully sent a label for FEC to MsgSource?
If not, goto LRq.13. (See Note 4.)
For Use Immediate OR LRq.12 Perform LSR Label Use procedure.
For Use If Loop Not Detected
1. Install label sent to MsgSource and label from Next For Use Immediate OR
Hop (if LSR is not egress) for forwarding/switching For Use If Loop Not Detected
use. 1. Install label sent to MsgSource and label from Next
Hop (if LSR is not egress) for forwarding/switching
use.
LRq.13 DONE LRq.13 DONE
Notes: Notes:
1. In the case where MsgSource is a non-label merging LSR it will 1. In the case where MsgSource is a non-label merging LSR it will
send a label request for each upstream LDP peer that has send a label request for each upstream LDP peer that has
requested a label for FEC from it. The LSR must be able to requested a label for FEC from it. The LSR must be able to
distinguish such requests from a non-label merging MsgSource distinguish such requests from a non-label merging MsgSource
from duplicate label requests. from duplicate label requests.
The LSR uses the message ID of received Label Request messages The LSR uses the message ID of received Label Request messages
to detect duplicate requests. This means that an LSR (the to detect duplicate requests. This means that an LSR (the
upstream peer) may not reuse the message ID used for a Label upstream peer) may not reuse the message ID used for a Label
Request until the Label Request transaction has completed. Request until the Label Request transaction has completed.
2. When an LSR sends a label request to a peer it records that the 2. When an LSR sends a label request to a peer it records that the
request has been sent and marks it as outstanding. As long as request has been sent and marks it as outstanding. As long as
the request is marked outstanding the LSR should not send the request is marked outstanding the LSR should not send
another request for the same label to the peer. Such a second another request for the same label to the peer. Such a second
request would be a duplicate. The Send_Label_Request procedure request would be a duplicate. The Send_Label_Request procedure
described below obeys this rule. described below obeys this rule.
A duplicate label request is considered a protocol error and A duplicate label request is considered a protocol error and
should be dropped by the receiving LSR (perhaps with a suitable should be dropped by the receiving LSR (perhaps with a suitable
notification returned to MsgSource). notification returned to MsgSource).
3. If LSR is not merge-capable, this test will fail. 3. If LSR is not merge-capable, this test will fail.
4. The Send_Label procedure may fail due to lack of label 4. The Send_Label procedure may fail due to lack of label
resources, in which case the LSR should not perform the Label resources, in which case the LSR should not perform the Label
Use procedure. Use procedure.
A.1.2. Receive Label Mapping A.1.2. Receive Label Mapping
Summary: Summary:
The response by an LSR to receipt of a FEC label mapping from an The response by an LSR to receipt of a FEC label mapping from an
LDP peer may involve one or more of the following actions: LDP peer may involve one or more of the following actions:
- Transmission of a label release message for the FEC label to the - Transmission of a label release message for the FEC label to
LDP peer; the LDP peer;
- Transmission of label mapping messages for the FEC to one or more - Transmission of label mapping messages for the FEC to one or
LDP peers, more LDP peers,
- Installation of the newly learned label for forwarding/switching - Installation of the newly learned label for
use by the LSR. forwarding/switching use by the LSR.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- MsgSource. The LDP peer that sent the message. - MsgSource. The LDP peer that sent the message.
- FEC. The FEC specified in the message. - FEC. The FEC specified in the message.
- Label. The label specified in the message. - Label. The label specified in the message.
- PrevAdvLabel. The label for FEC, if any, previously advertised to - PrevAdvLabel. The label for FEC, if any, previously advertised
an upstream peer. to an upstream peer.
- StoredHopCount. The hop count previously recorded for the FEC. - StoredHopCount. The hop count previously recorded for the FEC.
- RAttributes. Attributes received with the message. E.g., Hop - RAttributes. Attributes received with the message. E.g., Hop
Count, Path Vector. Count, Path Vector.
- SAttributes to be included in Label Mapping message, if any, - SAttributes to be included in Label Mapping message, if any,
propagated to upstream peers. propagated to upstream peers.
Algorithm: Algorithm:
LMp.1 Does the received label mapping match an outstanding label LMp.1 Does the received label mapping match an outstanding
request for FEC previously sent to MsgSource. label request for FEC previously sent to MsgSource.
If not, goto LMp.3. If not, goto LMp.3.
LMp.2 Delete record of outstanding FEC label request. LMp.2 Delete record of outstanding FEC label request.
LMp.3 Execute procedure Check_Received_Attributes (MsgSource, LMp.3 Execute procedure Check_Received_Attributes (MsgSource,
LabelMapping, RAttributes). LabelMapping, RAttributes).
If No Loop Detected, goto LMp.9. If No Loop Detected, goto LMp.9.
LMp.4 Does the LSR have a previously received label mapping for FEC LMp.4 Does the LSR have a previously received label mapping for
from MsgSource? (See Note 1.) FEC from MsgSource? (See Note 1.)
If not, goto LMp.8. (See Note 2.) If not, goto LMp.8. (See Note 2.)
LMp.5 Does the label previously received from MsgSource match Label LMp.5 Does the label previously received from MsgSource match
(i.e., the label received in the message)? (See Note 3.) Label (i.e., the label received in the message)?
If not, goto LMp.8. (See Note 4.) (See Note 3.)
If not, goto LMp.8. (See Note 4.)
LMp.6 Delete matching label mapping for FEC previously received LMp.6 Delete matching label mapping for FEC previously
from MsgSource. received from MsgSource.
LMp.7 Remove Label from forwarding/switching use. (See Note 5.) LMp.7 Remove Label from forwarding/switching use. (See Note 5.)
Goto LMp.33. Goto LMp.33.
LMp.8 Execute procedure Send_Message (MsgSource, Label Release, LMp.8 Execute procedure Send_Message (MsgSource, Label Release,
FEC, Label, Loop Detected Status code). Goto LMp.33. FEC, Label, Loop Detected Status code). Goto LMp.33.
LMp.9 Does LSR have a previously received label mapping for FEC LMp.9 Does LSR have a previously received label mapping for FEC
from MsgSource for the LSP in question? (See Note 6.) from MsgSource for the LSP in question? (See Note 6.)
If not, goto LMp.11. If not, goto LMp.11.
LMp.10 Does the label previously received from MsgSource match Label LMp.10 Does the label previously received from MsgSource match
(i.e., the label received in the message)? (See Note 3.) Label (i.e., the label received in the message)?
If not, goto LMp.32. (See Note 4.) (See Note 3.)
If not, goto LMp.32. (See Note 4.)
LMp.11 Determine the Next Hop for FEC. LMp.11 Determine the Next Hop for FEC.
LMp.12 Is MsgSource the Next Hop for FEC? LMp.12 Is MsgSource the Next Hop for FEC?
If so, goto LMp.14. If so, goto LMp.14.
LMp.13 Perform LSR Label Release procedure: LMp.13 Perform LSR Label Release procedure:
For Conservative Label retention: For Conservative Label retention:
1. Goto LMp.32. 1. Goto LMp.32.
For Liberal Label retention: For Liberal Label retention:
1. Record label mapping for FEC with Label and 1. Record label mapping for FEC with Label and
RAttributes has been received from MsgSource. RAttributes has been received from MsgSource.
Goto LMp.33. Goto LMp.33.
LMp.14 Is LSR an ingress for FEC? LMp.14 Is LSR an ingress for FEC?
If not, goto LMp.16. If not, goto LMp.16.
LMp.15 Install Label for forwarding/switching use. LMp.15 Install Label for forwarding/switching use.
LMp.16 Record label mapping for FEC with Label and RAttributes has LMp.16 Record label mapping for FEC with Label and RAttributes
been received from MsgSource. has been received from MsgSource.
LMp.17 Iterate through LMp.31 for each Peer. (See Note 7). LMp.17 Iterate through LMp.31 for each Peer. (See Note 7).
LMp.18 Has LSR previously sent a label mapping for FEC to Peer for LMp.18 Has LSR previously sent a label mapping for FEC to Peer
the LSP in question? (See Note 8.) for the LSP in question? (See Note 8.)
If so, goto LMp.22. If so, goto LMp.22.
LMp.19 Is the Downstream Unsolicited Ordered Control Label LMp.19 Is the Downstream Unsolicited Ordered Control Label
Distribution procedure being used by LSR? If not, goto Distribution procedure being used by LSR? If not, goto
LMp.28. LMp.28.
LMp.20 Execute procedure Prepare_Label_Mapping_Attributes(Peer, FEC, LMp.20 Execute procedure Prepare_Label_Mapping_Attributes(Peer,
RAttributes, SAttributes, IsPropagating, StoredHopCount). FEC, RAttributes, SAttributes, IsPropagating,
StoredHopCount).
LMp.21 Execute procedure Send_Message (Peer, Label Mapping, FEC, LMp.21 Execute procedure Send_Message (Peer, Label Mapping, FEC,
PrevAdvLabel, SAttributes). PrevAdvLabel, SAttributes).
Goto LMp.28 Goto LMp.28
LMp.22 Iterate through LMp.27 for each label mapping for FEC LMp.22 Iterate through LMp.27 for each label mapping for FEC
previously sent to Peer. previously sent to Peer.
LMp.23 Are RAttributes in the received label mapping consistent with LMp.23 Are RAttributes in the received label mapping consistent
those previously sent to Peer? with those previously sent to Peer?
If so, continue iteration from LMp.22 for next label mapping. If so, continue iteration from LMp.22 for next label
(See Note 9.) mapping. (See Note 9.)
LMp.24 Execute procedure Prepare_Label_Mapping_Attributes(Peer, FEC, LMp.24 Execute procedure Prepare_Label_Mapping_Attributes(Peer,
RAttributes, SAttributes, IsPropagating, StoredHopCount). FEC, RAttributes, SAttributes, IsPropagating,
StoredHopCount).
LMp.25 Execute procedure Send_Message (Peer, Label Mapping, FEC, LMp.25 Execute procedure Send_Message (Peer, Label Mapping, FEC,
PrevAdvLabel, SAttributes). (See Note 10.) PrevAdvLabel, SAttributes). (See Note 10.)
LMp.26 Update record of label mapping for FEC previously sent to LMp.26 Update record of label mapping for FEC previously sent to
Peer to include the new attributes sent. Peer to include the new attributes sent.
LMp.27 End iteration from LMp.22. LMp.27 End iteration from LMp.22.
LMp.28 Does LSR have any label requests for FEC from Peer marked as LMp.28 Does LSR have any label requests for FEC from Peer marked
pending? as pending?
If not, goto LMp.30. If not, goto LMp.30.
LMp.29 Perform LSR Label Distribution procedure: LMp.29 Perform LSR Label Distribution procedure:
For Downstream Unsolicited Independent Control OR For Downstream Unsolicited Independent Control OR
For Downstream Unsolicited Ordered Control For Downstream Unsolicited Ordered Control
1. Execute procedure 1. Execute procedure
Prepare_Label_Mapping_Attributes(Peer, FEC, Prepare_Label_Mapping_Attributes(Peer, FEC,
RAttributes, SAttributes, IsPropagating, RAttributes, SAttributes, IsPropagating,
UnknownHopCount). UnknownHopCount).
2. Execute procedure Send_Label (Peer, FEC, 2. Execute procedure Send_Label (Peer, FEC, SAttributes).
SAttributes). If the procedure fails, continue iteration for
If the procedure fails, continue iteration for next next Peer at LMp.17.
Peer at LMp.17.
3. If no pending requests exist for Peer goto LMp.30. 3. If no pending requests exist for Peer goto LMp.30.
(See Note 11.) (See Note 11.)
For Downstream On Demand Independent Control OR For Downstream On Demand Independent Control OR
For Downstream On Demand Ordered Control For Downstream On Demand Ordered Control
1. Iterate through Step 5 for each pending label request 1. Iterate through Step 5 for each pending label
for FEC from Peer marked as pending. request for FEC from Peer marked as pending.
2. Execute procedure 2. Execute procedure
Prepare_Label_Mapping_Attributes(Peer, FEC, Prepare_Label_Mapping_Attributes(Peer, FEC,
RAttributes, SAttributes, IsPropagating, RAttributes, SAttributes, IsPropagating,
UnknownHopCount) UnknownHopCount)
3. Execute procedure Send_Label (Peer, FEC, 3. Execute procedure Send_Label (Peer, FEC,
SAttributes). SAttributes).
If the procedure fails, continue iteration for next If the procedure fails, continue iteration for next
Peer at LMp.17. Peer at LMp.17.
4. Delete record of pending request. 4. Delete record of pending request.
5. End iteration from Step 1. 5. End iteration from Step 1.
6. Goto LMp.30. 6. Goto LMp.30.
LMp.30 Perform LSR Label Use procedure: LMp.30 Perform LSR Label Use procedure:
For Use Immediate OR For Use Immediate OR
For Use If Loop Not Detected For Use If Loop Not Detected
1. Iterate through Step 3 for each label mapping for FEC 1. Iterate through Step 3 for each label mapping for
previously sent to Peer. FEC previously sent to Peer.
2. Install label received and label sent to Peer for 2. Install label received and label sent to Peer for
forwarding/switching use. forwarding/switching use.
3. End iteration from Step 1. 3. End iteration from Step 1.
4. Goto LMp.31. 4. Goto LMp.31.
LMp.31 End iteration from LMp.17. LMp.31 End iteration from LMp.17.
Go to LMp.33. Go to LMp.33.
LMp.32 Execute procedure Send_Message (MsgSource, Label Release, LMp.32 Execute procedure Send_Message (MsgSource, Label Release,
FEC, Label). FEC, Label).
LMp.33 DONE. LMp.33 DONE.
Notes: Notes:
1. If the LSR is merging there should be at most 1 received 1. If the LSR is merging there should be at most 1 received
mapping for the FEC for the LSP in question. In the non-merging mapping for the FEC for the LSP in question. In the non-
case there could be multiple received mappings for the FEC for merging case there could be multiple received mappings for the
the LSP in question. FEC for the LSP in question.
2. If LSR has detected a loop and it has not previously received a 2. If LSR has detected a loop and it has not previously received
label mapping from MsgSource for the FEC, it simply releases a label mapping from MsgSource for the FEC, it simply releases
the label. the label.
3. Does the Label received in the message match any of the 1 or 3. Does the Label received in the message match any of the 1 or
more label mappings identified in the previous step (LMp.4 or more label mappings identified in the previous step (LMp.4 or
LMp.9)? LMp.9)?
4. An unsolicited mapping with a different label from the same 4. An unsolicited mapping with a different label from the same
peer would be an attempt to establish multipath label peer would be an attempt to establish multipath label
switching, which is not supported in this version of LDP. switching, which is not supported in this version of LDP.
5. If Label is not in forwarding/switching use, LMp.7 has no 5. If Label is not in forwarding/switching use, LMp.7 has no
effect. effect.
6. If the received label mapping message matched an outstanding 6. If the received label mapping message matched an outstanding
label request in LMp.1, then (by definition) LSR has not label request in LMp.1, then (by definition) LSR has not
previously received a label mapping for FEC for the LSP in previously received a label mapping for FEC for the LSP in
question. If the LSR is merging upstream labels for the LSP in question. If the LSR is merging upstream labels for the LSP
question, there should be at most 1 received mapping. In the in question, there should be at most 1 received mapping. In
non-merging case, there could be multiple received label the non-merging case, there could be multiple received label
mappings for the same FEC, one for each resulting LSP. mappings for the same FEC, one for each resulting LSP.
7. The LMp.17 iteration includes MsgSource in order to handle the 7. The LMp.17 iteration includes MsgSource in order to handle the
case where LSR is operating in Downstream Unsolicited ordered case where LSR is operating in Downstream Unsolicited ordered
control mode. Ordered control prevents LSR from advertising a control mode. Ordered control prevents LSR from advertising a
label for FEC until it has received a label mapping from its label for FEC until it has received a label mapping from its
next hop (MsgSource) for FEC. next hop (MsgSource) for FEC.
8. If LSR is merging the LSP it may have previously sent label 8. If LSR is merging the LSP it may have previously sent label
mappings for the FEC LSP to one or more peers. If LSR is not mappings for the FEC LSP to one or more peers. If LSR is not
merging, it may have sent a label mapping for the LSP in merging, it may have sent a label mapping for the LSP in
question to at most one LSR. question to at most one LSR.
9. The loop detection Path Vector attribute is considered in this 9. The loop detection Path Vector attribute is considered in this
check. If the received RAttributes include a Path Vector and check. If the received RAttributes include a Path Vector and
no Path Vector had been previously sent to the Peer, or if the no Path Vector had been previously sent to the Peer, or if the
received Path Vector is inconsistent with the Path Vector received Path Vector is inconsistent with the Path Vector
previously sent to the Peer, then the attributes are considered previously sent to the Peer, then the attributes are
to be inconsistent. Note that an LSR is not required to store considered to be inconsistent. Note that an LSR is not
a received Path Vector after it propagates the Path Vector in a required to store a received Path Vector after it propagates
mapping message. If an LSR does not store the Path Vector, it the Path Vector in a mapping message. If an LSR does not
has no way to check the consistency of a newly received Path store the Path Vector, it has no way to check the consistency
Vector. This means that whenever such an LSR receives a of a newly received Path Vector. This means that whenever
mapping message carrying a Path Vector it must always propagate such an LSR receives a mapping message carrying a Path Vector
the Path Vector. it must always propagate the Path Vector.
10. LMp.22 through LMp.27 deal with a situation that can arise when 10. LMp.22 through LMp.27 deal with a situation that can arise
the LSR is using independent control and it receives a mapping when the LSR is using independent control and it receives a
from the downstream peer after it has sent a mapping to an mapping from the downstream peer after it has sent a mapping
upstream peer. In this situation the LSR needs to propagate any to an upstream peer. In this situation the LSR needs to
changed attributes, such as Hop Count, upstream. If Loop propagate any changed attributes, such as Hop Count, upstream.
Detection is configured on, the propagated attributes must If Loop Detection is configured on, the propagated attributes
include the Path Vector must include the Path Vector
11. An LSR operating in Downstream Unsolicited mode must process 11. An LSR operating in Downstream Unsolicited mode must process
any Label Request messages it receives. If there are pending any Label Request messages it receives. If there are pending
label requests, fall through into the Downstream on Demand label requests, fall through into the Downstream on Demand
procedures in order to satisfy the pending requests. procedures in order to satisfy the pending requests.
A.1.3. Receive Label Abort Request A.1.3. Receive Label Abort Request
Summary: Summary:
When an LSR receives a label abort request message from a peer, it When an LSR receives a label abort request message from a peer, it
checks whether it has already responded to the label request in checks whether it has already responded to the label request in
question. If it has, it silently ignores the message. If it has question. If it has, it silently ignores the message. If it has
not, it sends the peer a Label Request Aborted Notification. In not, it sends the peer a Label Request Aborted Notification. In
addition, if it has a label request outstanding for the LSP in addition, if it has a label request outstanding for the LSP in
question to a downstream peer, it sends a Label Abort Request to question to a downstream peer, it sends a Label Abort Request to
the downstream peer to abort the LSP. the downstream peer to abort the LSP.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- MsgSource. The LDP peer that sent the message. - MsgSource. The LDP peer that sent the message.
- FEC. The FEC specified in the message. - FEC. The FEC specified in the message.
- RequestMessageID. The message ID of the label request message to - RequestMessageID. The message ID of the label request message
be aborted. to be aborted.
- Next Hop. The next hop for the FEC. - Next Hop. The next hop for the FEC.
Algorithm: Algorithm:
LAbR.1 Does the message match a previously received label request LAbR.1 Does the message match a previously received label request
message from MsgSource? (See Note 1.) message from MsgSource? (See Note 1.)
If not, goto LAbR.12. If not, goto LAbR.12.
LAbR.2 Has LSR responded to the previously received label request? LAbR.2 Has LSR responded to the previously received label
If so, goto LAbR.12. request?
If so, goto LAbR.12.
LAbR.3 Execute procedure Send_Message(MsgSource, Notification, Label LAbR.3 Execute procedure Send_Message(MsgSource, Notification,
Request Aborted, TLV), where TLV is the Label Request Message Label Request Aborted, TLV), where TLV is the Label
ID TLV received in the label abort request message. Request Message ID TLV received in the label abort
request message.
LAbR.4 Does LSR have a label request message outstanding for FEC? LAbR.4 Does LSR have a label request message outstanding for
If so, goto LAbR.7 FEC?
If so, goto LAbR.7
LAbR.5 Does LSR have a label mapping for FEC? LAbR.5 Does LSR have a label mapping for FEC?
If not, goto LAbR.11 If not, goto LAbR.11
LAbR.6 Generate Event: Received Label Release Message for FEC from LAbR.6 Generate Event: Received Label Release Message for FEC
MsgSource. (See Note 2.) from MsgSource. (See Note 2.)
Goto LAbR.11. Goto LAbR.11.
LAbR.7 Is LSR merging the LSP for FEC? LAbR.7 Is LSR merging the LSP for FEC?
If not, goto LAbR.9. If not, goto LAbR.9.
LAbR.8 Are there upstream peers other than MsgSource that have LAbR.8 Are there upstream peers other than MsgSource that have
requested a label for FEC? requested a label for FEC?
If so, goto LAbR.11. If so, goto LAbR.11.
LAbR.9 Execute procedure Send_Message (Next Hop, Label Abort LAbR.9 Execute procedure Send_Message (Next Hop, Label Abort
Request, FEC, TLV), where TLV is a Label Request Message ID Request, FEC, TLV), where TLV is a Label Request Message
TLV containing the Message ID used by the LSR in the ID TLV containing the Message ID used by the LSR in the
outstanding Label Request message. outstanding Label Request message.
LAbR.10 Record that a label abort request for FEC is pending. LAbR.10 Record that a label abort request for FEC is pending.
LAbR.11 Delete record of label request for FEC from MsgSource. LAbR.11 Delete record of label request for FEC from MsgSource.
LAbR.12 DONE LAbR.12 DONE
Notes: Notes:
1. LSR uses FEC and the Label Request Message ID TLV carried by 1. LSR uses FEC and the Label Request Message ID TLV carried by
the label abort request to locate its record (if any) for the the label abort request to locate its record (if any) for the
previously received label request from MsgSource. previously received label request from MsgSource.
2. If LSR has received a label mapping from NextHop, it should 2. If LSR has received a label mapping from NextHop, it should
behave as if it had advertised a label mapping to MsgSource and behave as if it had advertised a label mapping to MsgSource and
MsgSource has released it. MsgSource has released it.
A.1.4. Receive Label Release A.1.4. Receive Label Release
Summary: Summary:
When an LSR receives a label release message for a FEC from a peer, When an LSR receives a label release message for a FEC from a
it checks whether other peers hold the released label. If none do, peer, it checks whether other peers hold the released label. If
the LSR removes the label from forwarding/switching use, if it has none do, the LSR removes the label from forwarding/switching use,
not already done so, and if the LSR holds a label mapping from the if it has not already done so, and if the LSR holds a label
FEC next hop, it releases the label mapping. mapping from the FEC next hop, it releases the label mapping.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- MsgSource. The LDP peer that sent the message. - MsgSource. The LDP peer that sent the message.
- Label. The label specified in the message. - Label. The label specified in the message.
- FEC. The FEC specified in the message. - FEC. The FEC specified in the message.
Algorithm: Algorithm:
LRl.1 Remove MsgSource from record of peers that hold Label for LRl.1 Remove MsgSource from record of peers that hold Label for
FEC. (See Note 1.) FEC. (See Note 1.)
LRl.2 Does message match an outstanding label withdraw for FEC LRl.2 Does message match an outstanding label withdraw for FEC
previously sent to MsgSource? previously sent to MsgSource?
If not, goto LRl.4 If not, goto LRl.4
LRl.3 Delete record of outstanding label withdraw for FEC LRl.3 Delete record of outstanding label withdraw for FEC
previously sent to MsgSource. previously sent to MsgSource.
LRl.4 Is LSR merging labels for this FEC? LRl.4 Is LSR merging labels for this FEC?
If not, goto LRl.6. (See Note 2.) If not, goto LRl.6. (See Note 2.)
LRl.5 Has LSR previously advertised a label for this FEC to other LRl.5 Has LSR previously advertised a label for this FEC to
peers? other peers?
If so, goto LRl.10. If so, goto LRl.10.
LRl.6 Is LSR egress for the FEC? LRl.6 Is LSR egress for the FEC?
If so, goto LRl.10 If so, goto LRl.10
LRl.7 Is there a Next Hop for FEC? AND LRl.7 Is there a Next Hop for FEC? AND
Does LSR have a previously received label mapping for FEC Does LSR have a previously received label mapping for FEC
from Next Hop? from Next Hop?
If not, goto LRl.10. If not, goto LRl.10.
LRl.8 Is LSR configured to propagate releases? LRl.8 Is LSR configured to propagate releases?
If not, goto LRl.10. (See Note 3.) If not, goto LRl.10. (See Note 3.)
LRl.9 Execute procedure Send_Message (Next Hop, Label Release, FEC, LRl.9 Execute procedure Send_Message (Next Hop, Label Release,
Label from Next Hop). FEC, Label from Next Hop).
LRl.10 Remove Label from forwarding/switching use for traffic from LRl.10 Remove Label from forwarding/switching use for traffic
MsgSource. from MsgSource.
LRl.11 Do any peers still hold Label for FEC? LRl.11 Do any peers still hold Label for FEC?
If so, goto LRl.13. If so, goto LRl.13.
LRl.12 Free the Label. LRl.12 Free the Label.
LRl.13 DONE. LRl.13 DONE.
Notes: Notes:
1. If LSR is using Downstream Unsolicited label distribution, it 1. If LSR is using Downstream Unsolicited label distribution, it
should not re-advertise a label mapping for FEC to MsgSource should not re-advertise a label mapping for FEC to MsgSource
until MsgSource requests it. until MsgSource requests it.
2. LRl.4 through LRl.8 deal with determining whether where the LSR 2. LRl.4 through LRl.8 deal with determining whether where the LSR
should propagate the label release to a downstream peer should propagate the label release to a downstream peer
(LRl.9). (LRl.9).
3. If LRl.8 is reached, no upstream LSR holds a label for the FEC, 3. If LRl.8 is reached, no upstream LSR holds a label for the FEC,
and the LSR holds a label for the FEC from the FEC Next Hop. and the LSR holds a label for the FEC from the FEC Next Hop.
The LSR could propagate the Label Release to the Next Hop. By The LSR could propagate the Label Release to the Next Hop. By
propagating the Label Release the LSR releases a potentially propagating the Label Release the LSR releases a potentially
scarce label resource. In doing so, it also increases the scarce label resource. In doing so, it also increases the
latency for re-establishing the LSP should MsgSource or some latency for re-establishing the LSP should MsgSource or some
other upstream LSR send it a new Label Request for FEC. other upstream LSR send it a new Label Request for FEC.
Whether or not to propagate the release is not a protocol Whether or not to propagate the release is not a protocol
issue. Label distribution will operate properly whether or not issue. Label distribution will operate properly whether or not
the release is propagated. The decision to propagate or not the release is propagated. The decision to propagate or not
should take into consideration factors such as: whether labels should take into consideration factors such as: whether labels
are a scarce resource in the operating environment; the are a scarce resource in the operating environment; the
importance of keeping LSP setup latency low by keeping the importance of keeping LSP setup latency low by keeping the
amount of signaling required small; whether LSP setup is amount of signaling required small; whether LSP setup is
ingress-controlled or egress-controlled in the operating ingress-controlled or egress-controlled in the operating
environment. environment.
A.1.5. Receive Label Withdraw A.1.5. Receive Label Withdraw
Summary: Summary:
When an LSR receives a label withdraw message for a FEC from an LDP When an LSR receives a label withdraw message for a FEC from an
peer, it responds with a label release message and it removes the LDP peer, it responds with a label release message and it removes
label from any forwarding/switching use. If ordered control is in the label from any forwarding/switching use. If ordered control
use, the LSR sends a label withdraw message to each LDP peer to is in use, the LSR sends a label withdraw message to each LDP peer
which it had previously sent a label mapping for the FEC. If the to which it had previously sent a label mapping for the FEC. If
LSR is using Downstream on Demand label advertisement with the LSR is using Downstream on Demand label advertisement with
independent control, it then acts as if it had just recognized the independent control, it then acts as if it had just recognized the
FEC. FEC.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- MsgSource. The LDP peer that sent the message. - MsgSource. The LDP peer that sent the message.
- Label. The label specified in the message. - Label. The label specified in the message.
- FEC. The FEC specified in the message. - FEC. The FEC specified in the message.
Algorithm: Algorithm:
LWd.1 Remove Label from forwarding/switching use. (See Note 1.) LWd.1 Remove Label from forwarding/switching use. (See Note 1.)
LWd.2 Execute procedure Send_Message (MsgSource, Label Release, LWd.2 Execute procedure Send_Message (MsgSource, Label Release,
FEC, Label) FEC, Label)
LWd.3 Has LSR previously received and retained a matching label LWd.3 Has LSR previously received and retained a matching label
mapping for FEC from MsgSource? mapping for FEC from MsgSource?
If not, goto LWd.13. If not, goto LWd.13.
LWd.4 Delete matching label mapping for FEC previously received LWd.4 Delete matching label mapping for FEC previously received
from MsgSource. from MsgSource.
LWd.5 Is LSR using ordered control? LWd.5 Is LSR using ordered control?
If so, goto LWd.8. If so, goto LWd.8.
LWd.6 Is MsgSource using Downstream On Demand label advertisement? LWd.6 Is MsgSource using Downstream On Demand label
If not, goto LWd.13. advertisement?
If not, goto LWd.13.
LWd.7 Generate Event: Recognize New FEC for FEC. LWd.7 Generate Event: Recognize New FEC for FEC.
Goto LWd.13. (See Note 2.) Goto LWd.13. (See Note 2.)
LWd.8 Iterate through LWd.12 for each Peer, other than MsgSource. LWd.8 Iterate through LWd.12 for each Peer, other than
MsgSource.
LWd.9 Has LSR previously sent a label mapping for FEC to Peer? LWd.9 Has LSR previously sent a label mapping for FEC to Peer?
If not, continue iteration for next Peer at LWd.8. If not, continue iteration for next Peer at LWd.8.
LWd.10 Does the label previously sent to Peer "map" to the withdrawn LWd.10 Does the label previously sent to Peer "map" to the
Label? withdrawn Label?
If not, continue iteration for next Peer at LWd.8. (See Note If not, continue iteration for next Peer at LWd.8.
3.) (See Note 3.)
LWd.11 Execute procedure Send_Label_Withdraw (Peer, FEC, Label LWd.11 Execute procedure Send_Label_Withdraw (Peer, FEC, Label
previously sent to Peer). previously sent to Peer).
LWd.12 End iteration from LWd.8. LWd.12 End iteration from LWd.8.
LWd.13 DONE LWd.13 DONE
Notes: Notes:
1. If Label is not in forwarding/switching use, LWd.1 has no 1. If Label is not in forwarding/switching use, LWd.1 has no
effect. effect.
2. LWd.7 handles the case where the LSR is using Downstream On 2. LWd.7 handles the case where the LSR is using Downstream On
Demand label distribution with independent control. In this Demand label distribution with independent control. In this
situation the LSR should send a label request to the FEC next situation the LSR should send a label request to the FEC next
hop as if it had just recognized the FEC. hop as if it had just recognized the FEC.
3. LWd.10 handles both label merging (one or more incoming labels 3. LWd.10 handles both label merging (one or more incoming labels
map to the same outgoing label) and no label merging (one label map to the same outgoing label) and no label merging (one label
maps to the outgoing label) cases. maps to the outgoing label) cases.
A.1.6. Recognize New FEC A.1.6. Recognize New FEC
Summary: Summary:
The response by an LSR to learning a new FEC via the routing table The response by an LSR to learning a new FEC via the routing table
may involve one or more of the following actions: may involve one or more of the following actions:
- Transmission of label mappings for the FEC to one or more LDP - Transmission of label mappings for the FEC to one or more LDP
peers; peers;
- Transmission of a label request for the FEC to the FEC next hop; - Transmission of a label request for the FEC to the FEC next
hop;
- Any of the actions that can occur when the LSR receives a label - Any of the actions that can occur when the LSR receives a label
mapping for the FEC from the FEC next hop. mapping for the FEC from the FEC next hop.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- FEC. The newly recognized FEC. - FEC. The newly recognized FEC.
- Next Hop. The next hop for the FEC. - Next Hop. The next hop for the FEC.
- InitAttributes. Attributes to be associated with the new FEC. - InitAttributes. Attributes to be associated with the new FEC.
(See Note 1.) (See Note 1.)
- SAttributes. Attributes to be included in Label Mapping or Label - SAttributes. Attributes to be included in Label Mapping or
Request messages, if any, sent to peers. Label Request messages, if any, sent to peers.
- StoredHopCount. Hop count associated with FEC label mapping, if - StoredHopCount. Hop count associated with FEC label mapping,
any, previously received from Next Hop. if any, previously received from Next Hop.
Algorithm: Algorithm:
FEC.1 Perform LSR Label Distribution procedure: FEC.1 Perform LSR Label Distribution procedure:
For Downstream Unsolicited Independent Control For Downstream Unsolicited Independent Control
1. Iterate through 5 for each Peer. 1. Iterate through 5 for each Peer.
2. Has LSR previously received and retained a label 2. Has LSR previously received and retained a label
mapping for FEC from Next Hop? mapping for FEC from Next Hop?
If so, set Propagating to IsPropagating. If so, set Propagating to IsPropagating.
If not, set Propagating to NotPropagating. If not, set Propagating to NotPropagating.
3. Execute procedure Prepare_Label_Mapping_Attributes 3. Execute procedure Prepare_Label_Mapping_Attributes
(Peer, FEC, InitAttributes, SAttributes, Propagating, (Peer, FEC, InitAttributes, SAttributes, Propagating,
Unknown hop count(0)). Unknown hop count(0)).
4. Execute procedure Send_Label (Peer, FEC, SAttributes) 4. Execute procedure Send_Label (Peer, FEC, SAttributes)
5. End iteration from 1. 5. End iteration from 1.
Goto FEC.2. Goto FEC.2.
For Downstream Unsolicited Ordered Control For Downstream Unsolicited Ordered Control
1. Iterate through 5 for each Peer. 1. Iterate through 5 for each Peer.
2. Is LSR egress for the FEC? OR 2. Is LSR egress for the FEC? OR
Has LSR previously received and retained a label Has LSR previously received and retained a label
mapping for FEC from Next Hop? mapping for FEC from Next Hop?
If not, continue iteration for next Peer. If not, continue iteration for next Peer.
3. Execute procedure Prepare_Label_Mapping_Attributes 3. Execute procedure Prepare_Label_Mapping_Attributes
(Peer, FEC, InitAttributes, SAttributes, Propagating, (Peer, FEC, InitAttributes, SAttributes, Propagating,
StoredHopCount). StoredHopCount).
4. Execute procedure Send_Label (Peer, FEC, SAttributes) 4. Execute procedure Send_Label (Peer, FEC, SAttributes)
5. End iteration from 1. 5. End iteration from 1.
Goto FEC.2. Goto FEC.2.
For Downstream On Demand Independent Control OR For Downstream On Demand Independent Control OR
For Downstream On Demand Ordered Control For Downstream On Demand Ordered Control
1. Goto FEC.2. (See Note 2.) 1. Goto FEC.2. (See Note 2.)
FEC.2 Has LSR previously received and retained a label mapping for FEC.2 Has LSR previously received and retained a label
FEC from Next Hop? mapping for FEC from Next Hop?
If so, goto FEC.5 If so, goto FEC.5
FEC.3 Is Next Hop an LDP peer? FEC.3 Is Next Hop an LDP peer?
If not, Goto FEC.6 If not, Goto FEC.6
FEC.4 Perform LSR Label Request procedure: FEC.4 Perform LSR Label Request procedure:
For Request Never For Request Never
1. Goto FEC.6 1. Goto FEC.6
For Request When Needed OR For Request When Needed OR
For Request On Request For Request On Request
1. Execute procedure Prepare_Label_Request_Attributes 1. Execute procedure
(Next Hop, FEC, InitAttributes, SAttributes); Prepare_Label_Request_Attributes
(Next Hop, FEC, InitAttributes, SAttributes);
2. Execute procedure Send_Label_Request (Next Hop, FEC, 2. Execute procedure Send_Label_Request (Next
SAttributes). Hop, FEC, SAttributes).
Goto FEC.6. Goto FEC.6.
FEC.5 Generate Event: Received Label Mapping from Next Hop. (See FEC.5 Generate Event: Received Label Mapping from Next Hop.
Note 3.) (See Note 3.)
FEC.6 DONE. FEC.6 DONE.
Notes: Notes:
1. An example of an attribute that might be part of InitAttributes 1. An example of an attribute that might be part of InitAttributes
is one which specifies desired LSP characteristics, such as is one which specifies desired LSP characteristics, such as
class of service (CoS). (Note that while the current version class of service (CoS). (Note that while the current version
of LDP does not specify a CoS attribute, LDP extensions may.) of LDP does not specify a CoS attribute, LDP extensions may.)