draft-ietf-mpls-ldp-03.txt   draft-ietf-mpls-ldp-04.txt 
Network Working Group Loa Andersson Network Working Group Loa Andersson
Internet Draft Nortel Networks Inc. Internet Draft Nortel Networks Inc.
Expiration Date: July 1999 Expiration Date: November 1999
Paul Doolan Paul Doolan
Ennovate Networks Ennovate Networks
Nancy Feldman Nancy Feldman
IBM Corp IBM Corp
Andre Fredette Andre Fredette
Nortel Networks Inc. Nortel Networks Inc.
Bob Thomas Bob Thomas
Cisco Systems, Inc. Cisco Systems, Inc.
January 1999 May 1999
LDP Specification LDP Specification
draft-ietf-mpls-ldp-03.txt draft-ietf-mpls-ldp-04.txt
Status of this Memo Status of this Memo
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Abstract Abstract
An overview of Multi Protocol Label Switching (MPLS) is provided in An overview of Multi Protocol Label Switching (MPLS) is provided in
[FRAMEWORK] and a proposed architecture in [ARCH]. A fundamental [FRAMEWORK] and a proposed architecture in [ARCH]. A fundamental
concept in MPLS is that two Label Switching Routers (LSRs) must agree concept in MPLS is that two Label Switching Routers (LSRs) must agree
on the meaning of the labels used to forward traffic between and on the meaning of the labels used to forward traffic between and
through them. This common understanding is achieved by using the through them. This common understanding is achieved by using a set
Label Distribution Protocol (LDP) referenced in [ARCH]. This of procedures, called a label distribution protocol, by which one LSR
document defines the LDP protocol. informs another of label bindins it has made. This document defines
a set of such procedures called LDP (for Label Distribution
Protocol).
Changes from Previous Draft Changes from Previous Draft
- This draft includes by reference the CR-LDP-based and RSVP-based - This draft addresses issues raised during the LDP last call held
methods for establishing explicitly routed LSPs. February 8, 1999 through February 24, 1999.
- This draft modifies hop count procedures slightly for Label
Mapping messages to correctly support TTL maintenance for packets
traversing LSPs which include multiple clouds of devices which do
not perform 'TTL-decrement'.
- This draft removes the E-bit (Null Encapsulation bit) from the
ATM Session Parameters TLV used in the Initialization message
because draft-ietf-mpls-atm-01.txt leaves no encapsulation
parameters to negotiate at session setup time.
- This draft adds the D-bit, (VC Directionality bit) to the ATM
Session Paramameters TLV in order to allow interoperability with
ATM switches with 'paired' cross connects. When such a switch
establishes a VC in one direction, connectivity is established
automatically in the other direction.
- This draft specifies the representation of the Implicit NULL
label [see ARCH].
- This draft updates the procedure for the "Detect change in FEC
next hop" event in order to explicitly address the case where
there is no next hop.
- This draft expands the PVLim field of the Common Session
Parameters TLV to allow specification of loop detection path
vector length limits of up to 255.
- This draft corrects several errors of omission (e.g., failure to
specify certain TLV type codes, failure to note that Frame Relay,
like ATM, requires use of Hop Count TLV in Label Mapping and
Request messages), corrects numerous typos, and includes minor
re-wordings intended to clarify meaning.
Open Issues Open Issues
The following LDP issues are left unresolved with this version of the The following LDP issues are left unresolved with this version of the
spec: spec:
- LDP support for CoS is not completely specified in this version. - LDP support for CoS is not specified in this version. CoS
Cos support will be more fully 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 will be addressed in a future version. Multicast support will 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 will be addressed in a future this version. Multipath support will be addressed in a future
version. version.
Table of Contents Table of Contents
1 LDP Overview ....................................... 7 1 LDP Overview ....................................... 6
1.1 LDP Peers .......................................... 7 1.1 LDP Peers .......................................... 6
1.2 LDP Message Exchange ............................... 7 1.2 LDP Message Exchange ............................... 7
1.3 LDP Message Structure .............................. 8 1.3 LDP Message Structure .............................. 7
1.4 LDP Error Handling ................................. 8 1.4 LDP Error Handling ................................. 8
1.5 LDP Extensibility and Future Compatibility ......... 9 1.5 LDP Extensibility and Future Compatibility ......... 8
2 LDP Operation ...................................... 9 2 LDP Operation ...................................... 8
2.1 FECs ............................................... 9 2.1 FECs ............................................... 8
2.2 Label Spaces, Identifiers, Sessions and Transport .. 10 2.2 Label Spaces, Identifiers, Sessions and Transport .. 10
2.2.1 Label Spaces ....................................... 10 2.2.1 Label Spaces ....................................... 10
2.2.2 LDP Identifiers .................................... 11 2.2.2 LDP Identifiers .................................... 11
2.2.3 LDP Sessions ....................................... 11 2.2.3 LDP Sessions ....................................... 11
2.2.4 LDP Transport ...................................... 11 2.2.4 LDP Transport ...................................... 11
2.3 LDP Sessions between non-Directly Connected LSRs ... 12 2.3 LDP Sessions between non-Directly Connected LSRs ... 12
2.4 LDP Discovery ..................................... 12 2.4 LDP Discovery ..................................... 12
2.4.1 Basic Discovery Mechanism .......................... 12 2.4.1 Basic Discovery Mechanism .......................... 12
2.4.2 Extended Discovery Mechanism ....................... 13 2.4.2 Extended Discovery Mechanism ....................... 13
2.5 Establishing and Maintaining LDP Sessions .......... 14 2.5 Establishing and Maintaining LDP Sessions .......... 14
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2.6 Label Distribution and Management .................. 21 2.6 Label Distribution and Management .................. 21
2.6.1 Label Distribution Control Mode .................... 21 2.6.1 Label Distribution Control Mode .................... 21
2.6.1.1 Independent Label Distribution Control ............. 21 2.6.1.1 Independent Label Distribution Control ............. 21
2.6.1.2 Ordered Label Distribution Control ................. 21 2.6.1.2 Ordered Label Distribution Control ................. 21
2.6.2 Label Retention Mode ............................... 22 2.6.2 Label Retention Mode ............................... 22
2.6.2.1 Conservative Label Retention Mode .................. 22 2.6.2.1 Conservative Label Retention Mode .................. 22
2.6.2.2 Liberal Label Retention Mode ....................... 22 2.6.2.2 Liberal Label Retention Mode ....................... 22
2.6.3 Label Advertisement Mode ........................... 23 2.6.3 Label Advertisement Mode ........................... 23
2.7 LDP Identifiers and Next Hop Addresses ............. 23 2.7 LDP Identifiers and Next Hop Addresses ............. 23
2.8 Loop Detection ..................................... 24 2.8 Loop Detection ..................................... 24
2.8.1 Label Request Message .............................. 24 2.8.1 Label Request Message .............................. 25
2.8.2 Label Mapping Message .............................. 26 2.8.2 Label Mapping Message .............................. 26
2.8.3 Discussion ......................................... 27 2.8.3 Discussion ......................................... 28
2.9 Label Distribution for Explicitly Routed LSPs ...... 28 2.9 Label Distribution for Explicitly Routed LSPs ...... 28
3 Protocol Specification ............................. 28 3 Protocol Specification ............................. 29
3.1 LDP PDUs ........................................... 29 3.1 LDP PDUs ........................................... 29
3.2 LDP Procedures ..................................... 30 3.2 LDP Procedures ..................................... 30
3.3 Type-Length-Value Encoding ......................... 30 3.3 Type-Length-Value Encoding ......................... 30
3.4 TLV Encodings for Commonly Used Parameters ......... 32 3.4 TLV Encodings for Commonly Used Parameters ......... 32
3.4.1 FEC TLV ............................................ 32 3.4.1 FEC TLV ............................................ 32
3.4.1.1 FEC Procedures ..................................... 34 3.4.1.1 FEC Procedures ..................................... 35
3.4.2 Label TLVs ......................................... 34 3.4.2 Label TLVs ......................................... 35
3.4.2.1 Generic Label TLV .................................. 34 3.4.2.1 Generic Label TLV .................................. 35
3.4.2.2 ATM Label TLV ...................................... 35 3.4.2.2 ATM Label TLV ...................................... 35
3.4.2.3 Frame Relay Label TLV .............................. 36 3.4.2.3 Frame Relay Label TLV .............................. 36
3.4.3 Address List TLV ................................... 36 3.4.3 Address List TLV ................................... 37
3.4.4 COS TLV ............................................ 37 3.4.4 Hop Count TLV ...................................... 38
3.4.5 Hop Count TLV ...................................... 38 3.4.4.1 Hop Count Procedures ............................... 38
3.4.5.1 Hop Count Procedures ............................... 38 3.4.5 Path Vector TLV .................................... 39
3.4.6 Path Vector TLV .................................... 39 3.4.5.1 Path Vector Procedures ............................. 40
3.4.6.1 Path Vector Procedures ............................. 40 3.4.5.1.1 Label Request Path Vector .......................... 40
3.4.6.1.1 Label Request Path Vector .......................... 40 3.4.5.1.2 Label Mapping Path Vector .......................... 41
3.4.6.1.2 Label Mapping Path Vector .......................... 41 3.4.6 Status TLV ......................................... 42
3.4.7 Status TLV ......................................... 41
3.5 LDP Messages ....................................... 43 3.5 LDP Messages ....................................... 43
3.5.1 Notification Message ............................... 45 3.5.1 Notification Message ............................... 45
3.5.1.1 Notification Message Procedures .................... 46 3.5.1.1 Notification Message Procedures .................... 47
3.5.1.2 Events Signaled by Notification Messages ........... 46 3.5.1.2 Events Signaled by Notification Messages ........... 47
3.5.1.2.1 Malformed PDU or Message ........................... 47 3.5.1.2.1 Malformed PDU or Message ........................... 47
3.5.1.2.2 Unknown or Malformed TLV ........................... 47 3.5.1.2.2 Unknown or Malformed TLV ........................... 48
3.5.1.2.3 Session Hold Timer Expiration ...................... 48 3.5.1.2.3 Session KeepAlive Timer Expiration ................. 49
3.5.1.2.4 Unilateral Session Shutdown ........................ 48 3.5.1.2.4 Unilateral Session Shutdown ........................ 49
3.5.1.2.5 Initialization Message Events ...................... 48 3.5.1.2.5 Initialization Message Events ...................... 49
3.5.1.2.6 Events Resulting From Other Messages ............... 48 3.5.1.2.6 Events Resulting From Other Messages ............... 49
3.5.1.2.7 Miscellaneous Events ............................... 49 3.5.1.2.7 Miscellaneous Events ............................... 49
3.5.2 Hello Message ...................................... 49 3.5.2 Hello Message ...................................... 50
3.5.2.1 Hello Message Procedures ........................... 51 3.5.2.1 Hello Message Procedures ........................... 52
3.5.3 Initialization Message ............................. 52 3.5.3 Initialization Message ............................. 53
3.5.3.1 Initialization Message Procedures .................. 60 3.5.3.1 Initialization Message Procedures .................. 61
3.5.4 KeepAlive Message .................................. 60 3.5.4 KeepAlive Message .................................. 61
3.5.4.1 KeepAlive Message Procedures ....................... 60 3.5.4.1 KeepAlive Message Procedures ....................... 62
3.5.5 Address Message .................................... 61 3.5.5 Address Message .................................... 62
3.5.5.1 Address Message Procedures ......................... 61 3.5.5.1 Address Message Procedures ......................... 63
3.5.6 Address Withdraw Message ........................... 62 3.5.6 Address Withdraw Message ........................... 63
3.5.6.1 Address Withdraw Message Procedures ................ 62 3.5.6.1 Address Withdraw Message Procedures ................ 64
3.5.7 Label Mapping Message .............................. 63 3.5.7 Label Mapping Message .............................. 64
3.5.7.1 Label Mapping Message Procedures ................... 64 3.5.7.1 Label Mapping Message Procedures ................... 65
3.5.7.1.1 Independent Control Mapping ........................ 64 3.5.7.1.1 Independent Control Mapping ........................ 65
3.5.7.1.2 Ordered Control Mapping ............................ 65 3.5.7.1.2 Ordered Control Mapping ............................ 66
3.5.7.1.3 Downstream on Demand Label Advertisement ........... 65 3.5.7.1.3 Downstream on Demand Label Advertisement ........... 66
3.5.7.1.4 Downstream Unsolicited Label Advertisement ......... 66 3.5.7.1.4 Downstream Unsolicited Label Advertisement ......... 67
3.5.8 Label Request Message .............................. 66 3.5.8 Label Request Message .............................. 68
3.5.8.1 Label Request Message Procedures ................... 67 3.5.8.1 Label Request Message Procedures ................... 69
3.5.9 Label Withdraw Message ............................. 68 3.5.9 Label Abort Request Message ........................ 70
3.5.9.1 Label Withdraw Message Procedures .................. 69 3.5.9.1 Label Abort Request Message Procedures ............. 71
3.5.10 Label Release Message .............................. 70 3.5.10 Label Withdraw Message ............................. 72
3.5.10.1 Label Release Message Procedures ................... 71 3.5.10.1 Label Withdraw Message Procedures .................. 73
3.6 Messages and TLVs for Extensibility ................ 72 3.5.11 Label Release Message .............................. 74
3.6.1 LDP Vendor-private Extensions ...................... 72 3.5.11.1 Label Release Message Procedures ................... 74
3.6.1.1 LDP Vendor-private TLVs ............................ 72 3.6 Messages and TLVs for Extensibility ................ 75
3.6.1.2 LDP Vendor-private Messages ........................ 73 3.6.1 LDP Vendor-private Extensions ...................... 76
3.6.2 LDP Experimental Extensions ........................ 75 3.6.1.1 LDP Vendor-private TLVs ............................ 76
3.7 Message Summary .................................... 75 3.6.1.2 LDP Vendor-private Messages ........................ 77
3.8 TLV Summary ........................................ 76 3.6.2 LDP Experimental Extensions ........................ 78
3.9 Status Code Summary ................................ 77 3.7 Message Summary .................................... 79
3.10 Well-known Numbers ................................. 78 3.8 TLV Summary ........................................ 79
3.10.1 UDP and TCP Ports .................................. 78 3.9 Status Code Summary ................................ 80
3.10.2 Implicit NULL Label ................................ 78 3.10 Well-known Numbers ................................. 81
4 Security ........................................... 78 3.10.1 UDP and TCP Ports .................................. 81
4.1 The TCP MD5 Signature Option ....................... 78 3.10.2 Implicit NULL Label ................................ 81
4.2 LDP Use of the TCP MD5 Signature Option ............ 80 4 Security Considerations ............................ 81
5 Intellectual Property Considerations ............... 80 4.1 The TCP MD5 Signature Option ....................... 81
6 Acknowledgments .................................... 80 4.2 LDP Use of the TCP MD5 Signature Option ............ 83
7 References ......................................... 81 5 Intellectual Property Considerations ............... 84
8 Author Information ................................. 82 6 Acknowledgments .................................... 84
7 References ......................................... 84
8 Author Information ................................. 85
Appendix.A LDP Label Distribution Procedures .................. 83 Appendix.A LDP Label Distribution Procedures .................. 87
A.1 Handling Label Distribution Events ................. 85 A.1 Handling Label Distribution Events ................. 89
A.1.1 Receive Label Request .............................. 86 A.1.1 Receive Label Request .............................. 90
A.1.2 Receive Label Mapping .............................. 89 A.1.2 Receive Label Mapping .............................. 93
A.1.3 Receive Label Release .............................. 93 A.1.3 Receive Label Abort Request ........................ 97
A.1.4 Receive Label Withdraw ............................. 95 A.1.4 Receive Label Release .............................. 99
A.1.5 Recognize New FEC .................................. 96 A.1.5 Receive Label Withdraw ............................. 101
A.1.6 Detect change in FEC next hop ...................... 99 A.1.6 Recognize New FEC .................................. 102
A.1.7 Receive Notification / No Label Resources .......... 101 A.1.7 Detect Change in FEC Next Hop ...................... 105
A.1.8 Receive Notification / No Route .................... 102 A.1.8 Receive Notification / Label Request Aborted ....... 108
A.1.9 Receive Notification / Loop Detected ............... 103 A.1.9 Receive Notification / No Label Resources .......... 109
A.1.10 Receive Notification / Label Resources Available ... 103 A.1.10 Receive Notification / No Route .................... 109
A.1.11 Detect local label resources have become available . 104 A.1.11 Receive Notification / Loop Detected ............... 110
A.1.12 LSR decides to no longer label switch a FEC ........ 105 A.1.12 Receive Notification / Label Resources Available ... 111
A.1.13 Timeout of deferred label request .................. 105 A.1.13 Detect local label resources have become available . 111
A.2 Common Label Distribution Procedures ............... 106 A.1.14 LSR decides to no longer label switch a FEC ........ 112
A.2.1 Send_Label ......................................... 106 A.1.15 Timeout of deferred label request .................. 113
A.2.2 Send_Label_Request ................................. 108 A.2 Common Label Distribution Procedures ............... 114
A.2.3 Send_Label_Withdraw ................................ 109 A.2.1 Send_Label ......................................... 114
A.2.4 Send_Notification .................................. 109 A.2.2 Send_Label_Request ................................. 115
A.2.5 Send_Message ....................................... 110 A.2.3 Send_Label_Withdraw ................................ 117
A.2.6 Check_Received_Attributes .......................... 110 A.2.4 Send_Notification .................................. 117
A.2.7 Prepare_Label_Request_Attributes ................... 111 A.2.5 Send_Message ....................................... 118
A.2.8 Prepare_Label_Mapping_Attributes ................... 113 A.2.6 Check_Received_Attributes .......................... 118
A.2.7 Prepare_Label_Request_Attributes ................... 119
A.2.8 Prepare_Label_Mapping_Attributes ................... 121
1. LDP Overview 1. LDP Overview
LDP is the set of procedures and messages by which Label Switched Section 2.6 of the MPLS architecture [ARCH] defines a label
Routers (LSRs) establish Label Switched Paths (LSPs) through a distribution protocol as a set of procedures by which one Label
network by mapping network-layer routing information directly to Switched Router (LSR) informs another of the meaning of labels used
data-link layer switched paths. These LSPs may have an endpoint at a to forward traffic between and through them.
directly attached neighbor (comparable to IP hop-by-hop forwarding),
or may have an endpoint at a network egress node, enabling switching The MPLS architecture does not assume a single label distribution
via all intermediary nodes. protocol. In fact, a number of different label distribution
protocols are being standardized. Existing protocols have been
extended so that label distribution can be piggybacked on them. New
protocols have also been defined for the explicit purpose of
distributing labels. Section 2.29 of the architecture [ARCH]
discusses some of the considerations when chosing a label
distribution protocol for use in particular MPLS applications such as
Traffic Engineering [TE].
The Label Distribution Protocol (LDP) defined in this document is a
new protocol defined for distributing labels. It is the set of
procedures and messages by which Label Switched Routers (LSRs)
establish Label Switched Paths (LSPs) through a network by mapping
network-layer routing information directly to data-link layer
switched paths. These LSPs may have an endpoint at a directly
attached neighbor (comparable to IP hop-by-hop forwarding), or may
have an endpoint at a network egress node, enabling switching via all
intermediary nodes.
LDP associates a Forwarding Equivalence Class (FEC) [ARCH] with each LDP associates a Forwarding Equivalence Class (FEC) [ARCH] with each
LSP it creates. The FEC associated with an LSP specifies which 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.
Note that this document is written with respect to unicast routing This document assumes familiarity with the MPLS architecture [ARCH].
only. Multicast will be addressed in a future revision. Note that [ARCH] includes a glossary of MPLS terminology, such as
ingress, label switched path, etc.
1.1. LDP Peers 1.1. LDP Peers
Two LSRs which use LDP to exchange label/stream mapping information Two LSRs which use LDP to exchange label/stream mapping information
are known as "LDP Peers" with respect to that information and we are known as "LDP Peers" with respect to that information and we
speak of there being an "LDP Session" between them. A single LDP speak of there being an "LDP Session" between them. A single LDP
session allows each peer to learn the other's label mappings; i.e., session allows each peer to learn the other's label mappings; i.e.,
the protocol is bi-directional. the protocol is bi-directional.
1.2. LDP Message Exchange 1.2. LDP Message Exchange
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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.
2. LDP Operation 2. LDP Operation
2.1. FECs 2.1. FECs
It is necessary to precisely specify which IP packets may be mapped It is necessary to precisely specify which packets may be mapped to
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.
Each FEC is specified as a set of one or more FEC elements. Each FEC Each FEC is specified as a set of one or more FEC elements. Each FEC
element identifies a set of IP packets which may be mapped to the element identifies a set of packets which may be mapped to the
corresponding LSP. When an LSP is shared by multiple FEC elements, corresponding LSP. When an LSP is shared by multiple FEC elements,
that LSP is terminated at (or before) the node where the FEC elements that LSP is terminated at (or before) the node where the FEC elements
can no longer share the same path. can no longer share the same path.
Following are the currently defined types of FEC elements. New Following are the currently defined types of FEC elements. New
element types may be added as needed: element types may be added as needed:
1. IP Address Prefix. This element is an IP address prefix of any 1. Address Prefix. This element is an address prefix of any
length from 0 to 32 bits, inclusive. length from 0 to a full address, inclusive.
2. Host Address. This element is a 32-bit IP address. 2. Host Address. This element is a full host address.
We say that a particular IP address "matches" a particular IP address (We will see below that an Address Prefix FEC element which is a full
address has a different effect than a Host Address FEC element which
has the same address.)
We say that a particular address "matches" a particular address
prefix if and only if that address begins with that prefix. We also prefix if and only if that address begins with that prefix. We also
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 IP Address Prefix FEC element which matches the that LSP has an Address Prefix FEC element which matches the packet's
packet's IP destination address. With respect to a particular packet destination address. With respect to a particular packet and a
and a particular LSP, we refer to any IP Address Prefix FEC element particular LSP, we refer to any Address Prefix FEC element which
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 element
that is identical to the packet's IP destination address, then that is identical to the packet's destination address, then the
the packet is mapped to that LSP. packet is mapped to that LSP.
- If there multiple LSPs, each containing a Host Address FEC - If there multiple LSPs, each containing a Host Address FEC
element that is identical to the packet's IP 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 that
LSP. 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 whose
matching prefix is the longest. If there is no one LSP whose matching prefix is the longest. If there is no one LSP whose
matching prefix is longest, the packet is mapped to one from the matching prefix is longest, the packet is mapped to one from the
set of LSPs whose matching prefix is longer than the others. The set of LSPs whose matching prefix is longer than the others. The
procedure for selecting one of those LSPs is beyond the scope of procedure for selecting one of those LSPs is beyond the scope of
this document. 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 IP Address Prefix FEC router, and there is an LSP which has an Address Prefix FEC
element (of length 32 bits) which is an address of that router, element which is an address of that router, then the packet is
then the packet is mapped to that LSP. The procedure for mapped to that LSP. The procedure for obtaining this knowledge
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
particular egress router is beyond the scope of this document. (As
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.
As another example, if one is running BGP, it may be possible to
obtain this information from the BGP next hop attribute of the
packet's route.)
It is worth pointing out a few consequences of these rules:
- A packet may be sent on the LSP whose Address Prefix FEC element
is the address of the packet's egress router ONLY if there is no
LSP matching the packet's destination address.
- A packet may match two LSPs, one with a Host Address FEC element
and one with an Address Prefix FEC element. In this case, the
packet is always assigned to the former.
- A packet which does not match a particular Host Address FEC
element may not be sent on the corresponding LSP, even if the
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 labels.
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LDP uses the regular receipt of LDP Discovery Hellos to indicate a LDP uses the regular receipt of LDP Discovery Hellos to indicate a
peer's intent to use the label space identified by the Hello. An LSR peer's intent to use the label space identified by the Hello. An LSR
maintains a hold timer with each Hello adjacency which it restarts maintains a hold timer with each Hello adjacency which it restarts
when it receives a Hello that matches the adjacency. If the timer when it receives a Hello that matches the adjacency. If the timer
expires without receipt of a matching Hello from the peer, LDP expires without receipt of a matching Hello from the peer, LDP
concludes that the peer no longer wishes to label switch using that concludes that the peer no longer wishes to label switch using that
label space for that link (or target, in the case of Targeted Hellos) label space for that link (or target, in the case of Targeted Hellos)
or that the peer has failed. The LSR then deletes the Hello or that the peer has failed. The LSR then deletes the Hello
adjacency. When the last Hello adjacency for a LDP session is adjacency. When the last Hello adjacency for a LDP session is
deleted, the LSR terminates the LDP session by closing the transport deleted, the LSR terminates the LDP session by sending a Notification
connection. message and closing the transport connection.
2.5.6. Maintaining LDP Sessions 2.5.6. Maintaining LDP Sessions
LDP includes mechanisms to monitor the integrity of the LDP session. LDP includes mechanisms to monitor the integrity of the LDP session.
LDP uses the regular receipt of LDP PDUs on the session transport LDP uses the regular receipt of LDP PDUs on the session transport
connection to monitor the integrity of the session. An LSR maintains connection to monitor the integrity of the session. An LSR maintains
a KeepAlive timer for each peer session which it resets whenever it a KeepAlive timer for each peer session which it resets whenever it
receives an LDP PDU from the session peer. If the KeepAlive timer receives an LDP PDU from the session peer. If the KeepAlive timer
expires without receipt of an LDP PDU from the peer the LSR concludes expires without receipt of an LDP PDU from the peer the LSR concludes
skipping to change at page 22, line 8 skipping to change at page 22, line 8
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 1. The FEC refers to the LSR itself (including one of its directly
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, boundary, such as another area for OSPF summary networks, or
or another autonomous system for OSPF AS externals and BGP another autonomous system for OSPF AS externals and BGP routes
routes [rfc1583] [rfc1771]. [rfc1583] [rfc1771].
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
settings.
2.6.2. Label Retention Mode 2.6.2. Label Retention Mode
2.6.2.1. Conservative Label Retention Mode 2.6.2.1. Conservative Label Retention Mode
In Downstream Unsolicited advertisement mode, label mapping adver- In Downstream Unsolicited advertisement mode, label mapping
tisements for all routes may be received from all peer LSRs. When advertisements for all routes may be received from all peer LSRs.
using conservative label retention, advertised label mappings are When using conservative label retention, advertised label mappings
retained only if they will be used to forward packets (i.e., if they are retained only if they will be used to forward packets (i.e., if
are received from a valid next hop according to routing). If operat- they are received from a valid next hop according to routing). If
ing in Downstream on Demand mode, an LSR will request label mappings operating in Downstream on Demand mode, an LSR will request label
only from the next hop LSR according to routing. Since Downstream on mappings only from the next hop LSR according to routing. Since
Demand mode is primarily used when label conservation is desired Downstream on Demand mode is primarily used when label conservation
(e.g., an ATM switch with limited cross connect space), it is typi- is desired (e.g., an ATM switch with limited cross connect space), it
cally used with the conservative label retention mode. is typically used with the conservative label retention mode.
The main advantage of the conservative mode is that only the labels The main advantage of the conservative mode is that only the labels
that are required for the forwarding of data are allocated and main- that are required for the forwarding of data are allocated and
tained. This is particularly important in LSRs where the label space maintained. This is particularly important in LSRs where the label
is inherently limited, such as in an ATM switch. A disadvantage of space is inherently limited, such as in an ATM switch. A
the conservative mode is that if routing changes the next hop for a disadvantage of the conservative mode is that if routing changes the
given destination, a new label must be obtained from the new next hop next hop for a given destination, a new label must be obtained from
before labeled packets can be forwarded. the new next hop before labeled packets can be forwarded.
2.6.2.2. Liberal Label Retention Mode 2.6.2.2. Liberal Label Retention Mode
In Downstream Unsolicited advertisement mode, label mapping adver- In Downstream Unsolicited advertisement mode, label mapping
tisements for all routes may be received from all LDP peers. When advertisements for all routes may be received from all LDP peers.
using liberal label retention, every label mappings received from a When using liberal label retention, every label mappings received
peer LSR is retained regardless of whether the LSR is the next hop from a peer LSR is retained regardless of whether the LSR is the next
for the advertised mapping. When operating in Downstream on Demand hop for the advertised mapping. When operating in Downstream on
mode with liberal label retention, an LSR might choose to request Demand mode with liberal label retention, an LSR might choose to
label mappings for all known prefixes from all peer LSRs. Note, request label mappings for all known prefixes from all peer LSRs.
however, that Downstream on Demand mode is typically used by devices Note, however, that Downstream on Demand mode is typically used by
such as ATM switch-based LSRs for which the conservative approach is devices such as ATM switch-based LSRs for which the conservative
recommended. approach is recommended.
The main advantage of the liberal label retention mode is that reac- The main advantage of the liberal label retention mode is that
tion to routing changes can be quick because labels already exist. reaction to routing changes can be quick because labels already
The main disadvantage of the liberal mode is that unneeded label map- exist. The main disadvantage of the liberal mode is that unneeded
pings are distributed and maintained. label mappings are distributed and maintained.
2.6.3. Label Advertisement Mode 2.6.3. Label Advertisement Mode
Each interface on an LSR is configured to operate in either Down- Each interface on an LSR is configured to operate in either
stream Unsolicited or Downstream on Demand advertisement mode. LSRs Downstream Unsolicited or Downstream on Demand advertisement mode.
exchange advertisement modes during initialization. The major LSRs exchange advertisement modes during initialization. The major
difference between Downstream Unsolicited and Downstream on Demand difference between Downstream Unsolicited and Downstream on Demand
modes is in which LSR takes responsibility for initiating mapping modes is in which LSR takes responsibility for initiating mapping
requests and mapping advertisements. requests and mapping advertisements.
2.7. LDP Identifiers and Next Hop Addresses 2.7. LDP Identifiers and Next Hop Addresses
An LSR maintains learned labels in a Label Information Base (LIB). An LSR maintains learned labels in a Label Information Base (LIB).
When operating in Downstream Unsolicited mode, the LIB entry for an When operating in Downstream Unsolicited mode, the LIB entry for an
address prefix associates a collection of (LDP Identifier, label) address prefix associates a collection of (LDP Identifier, label)
pairs with the prefix, one such pair for each peer advertising a pairs with the prefix, one such pair for each peer advertising a
label for the prefix. label for the prefix.
When the next hop for a prefix changes the LSR must retrieve the When the next hop for a prefix changes the LSR must retrieve the
label advertised by the new next hop from the LIB for use in forward- label advertised by the new next hop from the LIB for use in
ing. To retrieve the label the LSR must be able to map the next hop forwarding. To retrieve the label the LSR must be able to map the
address for the prefix to an LDP Identifier. next hop address for the prefix to an LDP Identifier.
Similarly, when the LSR learns a label for a prefix from an LDP peer, Similarly, when the LSR learns a label for a prefix from an LDP peer,
it must be able to determine whether that peer is currently a next it must be able to determine whether that peer is currently a next
hop for the prefix to determine whether it needs to start using the hop for the prefix to determine whether it needs to start using the
newly learned label when forwarding packets that match the prefix. newly learned label when forwarding packets that match the prefix.
To make that decision the LSR must be able to map an LDP Identifier To make that decision the LSR must be able to map an LDP Identifier
to the peer's addresses to check whether any are a next hop for the to the peer's addresses to check whether any are a next hop for the
prefix. prefix.
To enable LSRs to map between a peer LDP identifier and the peer's To enable LSRs to map between a peer LDP identifier and the peer's
addresses, LSRs advertise their addresses using LDP Address and With- addresses, LSRs advertise their addresses using LDP Address and
draw Address messages. Withdraw Address messages.
An LSR sends an Address message to advertise its addresses to a peer. An LSR sends an Address message to advertise its addresses to a peer.
An LSR sends a Withdraw Address message to withdraw previously adver- An LSR sends a Withdraw Address message to withdraw previously
tised addresses from a peer advertised addresses from a peer
2.8. Loop Detection 2.8. Loop Detection
Loop detection is a configurable option which provides a mechanism Loop detection is a configurable option 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 containing
message has traversed. An LSR is identified in a Path Vector message has traversed. An LSR is identified in a Path Vector
list by its unique LSR Identifier (Id), which is the IP address list by its unique LSR Identifier (Id), which is the IP address
component of its LDP Identifier. When an LSR propagates a mes- component of its LDP Identifier. When an LSR propagates a
sage containing a Path Vector TLV it adds its LSR Id to the Path message containing a Path Vector TLV it adds its LSR Id to the
Vector list. An LSR that receives a message with a Path Vector Path Vector list. An LSR that receives a message with a Path
that contains its LSR Id detects that the message has traversed a Vector that contains its LSR Id detects that the message has
loop. LDP supports the notion of a maximum allowable Path Vector traversed a loop. LDP supports the notion of a maximum allowable
length; an LSR that detects a Path Vector has reached the maximum Path Vector length; an LSR that detects a Path Vector has reached
length behaves as if the containing message has traversed a loop. 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 containing
message has traversed. When an LSR propagates a message contain- message has traversed. When an LSR propagates a message
ing a Hop Count TLV it increments the count. An LSR that detects containing a Hop Count TLV it increments the count. An LSR that
a Hop Count has reached a configured maximum value behaves as if detects a Hop Count has reached a configured maximum value
the containing message has traversed a loop. By convention a behaves as if the containing message has traversed a loop. By
count of 0 is interpreted to mean the hop count is unknown. convention a count of 0 is interpreted to mean the hop count is
Incrementing an unknown hop count value results in an unknown hop unknown. Incrementing an unknown hop count value results in an
count value (0). unknown hop count value (0).
The following paragraphs describes LDP loop detection procedures. In The following paragraphs describes LDP loop detection procedures. In
these paragraphs, "MUST" means "MUST if configured for loop detec- these paragraphs, "MUST" means "MUST if configured for loop
tion". The paragraphs specify messages that must carry Path Vector detection". The paragraphs specify messages that must carry Path
and Hop Count TLVs. Note that the Hop Count TLV and its procedures Vector and Hop Count TLVs. Note that the Hop Count TLV and its
are used without the Path Vector TLV in situations when loop detec- procedures are used without the Path Vector TLV in situations when
tion is not configured (see [ATM] and [FR]). loop detection is not configured (see [ATM] and [FR]).
2.8.1. Label Request Message 2.8.1. Label Request Message
The use of the Path Vector TLV and Hop Count TLV prevent Label The use of the Path Vector TLV and Hop Count TLV prevent Label
Request messages from looping in environments that include non-merge Request messages from looping in environments that include non-merge
capable LSRs. capable LSRs.
The rules that govern use of the Hop Count TLV in Label Request mes- The rules that govern use of the Hop Count TLV in Label Request
sages by LSR R when Loop Detection is enabled are the following: messages by LSR R when Loop Detection is enabled are the following:
- The Label Request message MUST include a Hop Count TLV. - The Label Request message MUST include a Hop Count TLV.
- If R is sending the Label Request because it is a FEC ingress, it - If R is sending the Label Request because it is a FEC ingress, it
MUST include a Hop Count TLV with hop count value 1. MUST include a Hop Count TLV with hop count value 1.
- If R is sending the Label Request as a result of having received a - If R is sending the Label Request as a result of having received a
Label Request from an upstream LSR, and if the received Label Label Request from an upstream LSR, and if the received Label
Request contains a Hop Count TLV, R MUST increment the received hop Request contains a Hop Count TLV, R MUST increment the received hop
count value by 1 and MUST pass the resulting value in a Hop Count count value by 1 and MUST pass the resulting value in a Hop Count
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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
the newly received Label Request with the existing outstanding Label the newly received Label Request with the existing outstanding Label
Request, then R does not propagate the Label Request to the next hop. Request, then R does not propagate the Label Request to the next hop.
If R receives a Label Request message from its next hop with a Hop If R receives a Label Request message from its next hop with a Hop
Count TLV which exceeds the configured maximum value, or with a 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 Label Request message has allowable length, then R detects that the Label Request message has
traveled in a loop. traveled in a loop.
When R detects a loop, it MUST send a Loop Detected Notification mes- When R detects a loop, it MUST send a Loop Detected Notification
sage to the source of the Label Request message and drop the Label message to the source of the Label Request message and drop the Label
Request message. Request message.
2.8.2. Label Mapping Message 2.8.2. Label Mapping Message
The use of the Path Vector TLV and Hop Count TLV in the Label Mapping The use of the Path Vector TLV and Hop Count TLV in the Label Mapping
message provide a mechanism to find and terminate looping LSPs. When message provide a mechanism to find and terminate looping LSPs. When
an LSR receives a Label Mapping message from a next hop, the message an LSR receives a Label Mapping message from a next hop, the message
is propagated upstream as specified below until an ingress LSR is is propagated upstream as specified below until an ingress LSR is
reached or a loop is found. reached or a loop is found.
The rules that govern the use of the Hop Count TLV in Label Mapping The rules that govern the use of the Hop Count TLV in Label Mapping
messages sent by an LSR R when Loop Detection is enabled are the fol- messages sent by an LSR R when Loop Detection is enabled are the
lowing: following:
- R MUST include a Hop Count TLV. - R MUST include a Hop Count TLV.
- If R is the egress, the hop count value MUST be 1. - If R is the egress, the hop count value MUST be 1.
- If the Label Mapping message is being sent to propagate a Label - If the Label Mapping message is being sent to propagate a Label
Mapping message received from the next hop to an upstream peer, the Mapping message received from the next hop to an upstream peer, the
hop count value MUST be determined as follows: 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, R
MUST reset the hop count to 1 before propagating the message. 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 next
hop before propagating the message. 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 Label
Mapping message, the hop count value MUST be the result of incre- Mapping message, the hop count value MUST be the result of
menting R's current knowledge of the hop count learned from previ- incrementing R's current knowledge of the hop count learned from
ous Label Mapping messages. Note that this hop count value will be previous Label Mapping messages. Note that this hop count value
unknown if R has not received a Label Mapping message from the next will be unknown if R has not received a Label Mapping message from
hop. the next hop.
Any Label Mapping message MAY contain a Path Vector TLV. The rules Any Label Mapping message MAY contain a Path Vector TLV. The rules
that govern the mandatory use of the Path Vector TLV in Label Mapping that govern the mandatory use of the Path Vector TLV in Label Mapping
messages sent by LSR R when Loop Detection is enabled are the follow- messages sent by LSR R when Loop Detection is enabled are the
ing: following:
- If R is the egress, the Label Mapping message need not include a - If R is the egress, the Label Mapping message need not include a
Path Vector TLV. Path Vector TLV.
- If R is sending the Label Mapping message to propagate a Label Map- - If R is sending the Label Mapping message to propagate a Label
ping message received from the next hop to an upstream peer, then: Mapping message received from the next hop to an upstream peer,
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
skipping to change at page 28, line 24 skipping to change at page 28, line 36
upstream. Thus, it is recommended that loop detection be configured upstream. Thus, it is recommended that loop detection be configured
in conjunction with ordered label distribution, to minimize the in conjunction with ordered label distribution, to minimize the
number of Label Mapping update messages. number of Label Mapping update messages.
If loop detection is desired in an MPLS domain, then it should be If loop detection is desired in an MPLS domain, then it should be
turned on in ALL LSRs within that MPLS domain, else loop detection turned on in ALL LSRs within that MPLS domain, else loop detection
will not operate properly. will not operate properly.
2.9. Label Distribution for Explicitly Routed LSPs 2.9. Label Distribution for Explicitly Routed LSPs
Traffic Engineering [TE] is expected to be an important MPLS applica- Traffic Engineering [TE] is expected to be an important MPLS
tion. It uses explicitly routed LSPs, which need not follow application. MPLS support for Traffic Engineering uses explicitly
normally-routed (hop-by-hop) paths as determined by destination-based routed LSPs, which need not follow normally-routed (hop-by-hop) paths
routing protocols. as determined by destination-based routing protocols. CR-LDP [CRLDP]
defines extensions to LDP to use LDP to set up explicitly routed
Two approaches for establishing explictily routed LSPs are under LSPs.
development within the MPLS WG. One approach [CRLDP] uses extensions
to LDP to accomplish label distribution; the other [LSPTUN] uses
extensions to RSVP [rfc2205].
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.
This section specifies the message encodings and procedures for pro- This section specifies the message encodings and procedures for
cessing the messages. processing the messages.
LDP message exchanges are accomplished by sending LDP protocol data LDP message exchanges are accomplished by sending LDP protocol data
units (PDUs) over LDP session TCP connections. units (PDUs) over LDP session TCP connections.
Each LDP PDU can carry one or more LDP messages. Note that the mes- Each LDP PDU can carry one or more LDP messages. Note that the
sages in an LDP PDU need not be related to one another. For example, messages in an LDP PDU need not be related to one another. For
a single PDU could carry a message advertising FEC-label bindings for example, a single PDU could carry a message advertising FEC-label
several FECs, another message requesting label bindings for several bindings for several FECs, another message requesting label bindings
other FECs, and a third notification message signaling some event. for several other FECs, and a third notification message signaling
some event.
3.1. LDP PDUs 3.1. LDP PDUs
Each LDP PDU is an LDP header followed by one or more LDP messages. Each LDP PDU is an LDP header followed by one or more LDP messages.
The LDP header is: The LDP header is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | PDU Length | | Version | PDU Length |
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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 for which Six octet field that uniquely identifies the label space of the
this PDU applies. The first four octets encode an IP address sending LSR for which this PDU applies. The first four octets
assigned to the LSR. This address should be the router-id, also encode an IP address assigned to the LSR. This address should be
used to identify the LSR in loop detection Path Vectors. The last the router-id, also used to identify the LSR in loop detection Path
two octets identify a label space within the LSR. For a platform- Vectors. The last two octets identify a label space within the
wide label space, these should both be zero. LSR. For a platform-wide label space, these should both be zero.
Note that there is no alignment requirement for the first octet of an Note that there is no alignment requirement for the first octet of an
LDP PDU. LDP PDU.
3.2. LDP Procedures 3.2. LDP Procedures
LDP defines messages, TLVs and procedures in the following areas: LDP defines messages, TLVs and procedures in the following areas:
- Peer discovery; - Peer discovery;
- Session management; - Session management;
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type | Length | |U|F| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Value | | Value |
~ ~ ~ ~
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit U bit
Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear
(=0), a notification must be returned to the message originator and (=0), a notification must be returned to the message originator and
the entire message must be ignored; if U is set (=1), the unknown the entire message must be ignored; if U is set (=1), the unknown
TLV is silently ignored and the rest of the message is processed as TLV is silently ignored and the rest of the message is processed as
if the unknown TLV did not exist. if the unknown TLV did not exist. The sections following that
define TLVs specify a value for the U-bit.
F bit F bit
Forward unknown TLV bit. This bit applies only when the U bit is Forward unknown TLV bit. This bit applies only when the U bit is
set and the LDP message containing the unknown TLV is to be for- set and the LDP message containing the unknown TLV is to be
warded. If F is clear (=0), the unknown TLV is not forwarded with forwarded. If F is clear (=0), the unknown TLV is not forwarded
the containing message; if F is set (=1), the unknown TLV is for- with the containing message; if F is set (=1), the unknown TLV is
warded with the containing message. forwarded with the containing message. The sections following 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 inter- Octet string of Length octets that encodes information to be
preted as specified by the Type field. interpreted as specified by the Type field.
Note that there is no alignment requirement for the first octect of a Note that there is no alignment requirement for the first octect of a
TLV. TLV.
Note that the Value field itself may contain TLV encodings. That is, Note that the Value field itself may contain TLV encodings. That is,
TLVs may be nested. TLVs may be nested.
The TLV encoding scheme is very general. In principle, everything The TLV encoding scheme is very general. In principle, everything
appearing in an LDP PDU could be encoded as a TLV. This specifica- appearing in an LDP PDU could be encoded as a TLV. This
tion does not use the TLV scheme to its full generality. It is not specification does not use the TLV scheme to its full generality. It
used where its generality is unnecessary and its use would waste is not used where its generality is unnecessary and its use would
space unnecessarily. These are usually places where the type of a waste space unnecessarily. These are usually places where the type
value to be encoded is known, for example by its position in a mes- of a value to be encoded is known, for example by its position in a
sage or an enclosing TLV, and the length of the value is fixed or message or an enclosing TLV, and the length of the value is fixed or
readily derivable from the value encoding itself. readily derivable from the value encoding itself.
Some of the TLVs defined for LDP are similar to one another. For Some of the TLVs defined for LDP are similar to one another. For
example, there is a Generic Label TLV, an ATM Label TLV, and a Frame example, there is a Generic Label TLV, an ATM Label TLV, and a Frame
Relay TLV; see Sections "Generic Label TLV", "ATM Label TLV", and Relay TLV; see Sections "Generic Label TLV", "ATM Label TLV", and
"Frame Relay TLV". "Frame Relay TLV".
While it is possible to think about TLVs related in this way in terms While it is possible to think about TLVs related in this way in terms
of a TLV type that specifies a TLV class and a TLV subtype that of a TLV type that specifies a TLV class and a TLV subtype that
specifies a particular kind of TLV within that class, this specifica- specifies a particular kind of TLV within that class, this
tion does not formalize the notion of a TLV subtype. specification does not formalize the notion of a TLV subtype.
The specification assigns type values for related TLVs, such as the The specification assigns type values for related TLVs, such as the
label TLVs, from a contiguous block in the 16-bit TLV type number label TLVs, from a contiguous block in the 16-bit TLV type number
space. space.
Section "TLV Summary" lists the TLVs defined in this version of the Section "TLV Summary" lists the TLVs defined in this version of the
protocol and the section in this document that describes each. protocol and the section in this document that describes each.
3.4. TLV Encodings for Commonly Used Parameters 3.4. TLV Encodings for Commonly Used Parameters
skipping to change at page 32, line 28 skipping to change at page 33, line 8
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| FEC (0x0100) | Length | |0|0| FEC (0x0100) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element 1 | | FEC Element 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element n | | FEC Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 33, line 11 skipping to change at page 33, line 37
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 4 octet full IP address; see below. Host Address 0x03 Full host address; see below.
Note that this version of LDP supports the use of multiple FEC
Elements per FEC for the Label Mapping message only. The use of
multiple FEC Elements in other messages is not permitted in this
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 Messages.
Indicates the withdraw/release is to be applied to all FECs asso- Indicates the withdraw/release is to be applied to all FECs
ciated with the label within the following label TLV. Must be associated with the label within the following label TLV. Must
the only FEC Element in the FEC TLV. 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. address prefix that follows. A length of zero indicates a
prefix that matches all addresses (the default destination); in
this case the Prefix itself is zero octets).
Prefix Prefix
An address prefix encoded according to the Address Family An address prefix encoded according to the Address Family
field, whose length, in bits, was specified in the PreLen field, whose length, in bits, was specified in the PreLen
field, padded to a byte boundary. field, padded to a byte boundary.
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
skipping to change at page 34, line 28 skipping to change at page 35, line 8
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 type it can- If in decoding a FEC TLV an LSR encounters a FEC Element type it
not decode, it should stop decoding the FEC TLV, abort processing the cannot decode, it should stop decoding the FEC TLV, abort processing
message containing the TLV, and send an Notification message to its the message containing the TLV, and send an Notification message to
LDP peer signaling an error. its LDP peer signaling an error.
3.4.2. Label TLVs 3.4.2. Label TLVs
Label TLVs encode labels. Label TLVs are carried by the messages Label TLVs encode labels. Label TLVs are carried by the messages
used to advertise, request, release and withdraw label mappings. used to advertise, request, release and withdraw label mappings.
There are several different kinds of Label TLVs which can appear in There are several different kinds of Label TLVs which can appear in
situations that require a Label TLV. situations that require a Label TLV.
3.4.2.1. Generic Label TLV 3.4.2.1. Generic Label TLV
An LSR uses Generic Label TLVs to encode labels for use on links for An LSR uses Generic Label TLVs to encode labels for use on links for
which label values are independent of the underlying link technology. which label values are independent of the underlying link technology.
Examples of such links are PPP and Ethernet. Examples of such links are PPP and Ethernet.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 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 [ENCAP] represented as
a 20-bit number in a 4 octet field. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 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 and
must be ignored on receipt. 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 VCI
are significant. If V-bits is 01, only the VPI field is signifi- are significant. If V-bits is 01, only the VPI field is
cant. If V-bit is 10, only the VCI is significant. significant. If V-bit is 10, only the VCI is significant.
VPI VPI
Virtual Path Identifier. If VPI is less than 12-bits it should be Virtual Path Identifier. If VPI is less than 12-bits it should be
right justified in this field and preceding bits should be set to right justified in this field and preceding bits should be set to
0. 0.
VCI VCI
Virtual Channel Identifier. If the VCI is less than 16- bits, it Virtual Channel Identifier. If the VCI is less than 16- bits, it
should be right justified in the field and the preceding bits must should be right justified in the field and the preceding bits must
be set to 0. If Virtual Path switching is indicated in the V-bits be set to 0. If Virtual Path switching is indicated in the V-bits
skipping to change at page 36, line 13 skipping to change at page 36, line 42
by the sender. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 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 and
must be ignored on receipt. 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 following
skipping to change at page 36, line 36 skipping to change at page 37, line 19
0 = 10 bits DLCI 0 = 10 bits DLCI
1 = 17 bits DLCI 1 = 17 bits DLCI
2 = 23 bits DLCI 2 = 23 bits DLCI
DLCI DLCI
The Data Link Connection Identifier. Refer to [FR] for the label The Data Link Connection Identifier. Refer to [FR] for the label
values and formats. 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 mes- The Address List TLV appears in Address and Address Withdraw
sages. messages.
Its encoding is: Its encoding is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Address List (0x0101) | Length | |0|0| Address List (0x0101) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 encod- A list of addresses from the specified Address Family. The
ing 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
3.4.4. COS TLV 3.4.4. Hop Count TLV
The COS (Class of Service) TLV may appear as an optional field in
messages that request and carry label mappings. It is used to
request and advertise (Label, FEC, class of service) bindings. Its
encoding is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| COS (0x0102) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| COS Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
COS Value
The value field for this TLV is a subject for further study.
One possibility is to define a set of CoS values that map to Dif-
ferentiated Services [DIFFSERV] code points. Other CoS values
could be supported in addition to or in place of the Differentiated
Services code points.
3.4.5. 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 [ATM] and [FR]).
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 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.
3.4.5.1. 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:
skipping to change at page 39, line 19 skipping to change at page 39, line 15
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 signalling
overhead when independent control is used. When a new LSP is
established, each LSR starts with unknown hop count. Addition of a
new LSR whose hop count is also unknown does not cause a hop count
update to be propagated upstream since the hop count remains unknown.
When the egress is finally added to the LSP, then the LSRs propagate
hop count updates upstream via Label Mapping messages.
Without use of the unknown hop count, each time a new LSR is added to
the LSP a hop count update would need to be propagated upstream if
the new LSR is closer to the egress than any of the other LSRs.
These updates are useless overhead since they don't reflect the hop
count to the egress.
From the perspective of the ingress node, the fact that the hop count
is unknown implies nothing about whether a packet sent on the LSP
will actually make it to the egress. All it implies is that the hop
count update from the egress has not yet reached the ingress.
If an LSR receives a message containing a Hop Count TLV, it must If an LSR receives a message containing a Hop Count TLV, it must
check the hop count value to determine whether the hop count has check the hop count value to determine whether the hop count has
exceeded its configured maximum allowable value. If so, it must exceeded its configured maximum allowable value. If so, it must
behave as if the containing message has traversed a loop by sending a behave as if the containing message has traversed a loop by sending a
Notification message signaling Loop Detected in reply to the sender Notification message signaling Loop Detected in reply to the sender
of the message. of the message.
If Loop Detection is configured, the LSR must follow the procedures If Loop Detection is configured, the LSR must follow the procedures
specified in Section "Loop Detection". specified in Section "Loop Detection".
3.4.6. Path Vector TLV 3.4.5. Path Vector TLV
The Path Vector TLV is used with the Hop Count TLV in Label Request The Path Vector TLV is used with the Hop Count TLV in Label Request
and Label Mapping messages to implement the optional LDP loop detec- and Label Mapping messages to implement the optional LDP loop
tion mechanism. See Section "Loop Detection". Its use in the Label detection mechanism. See Section "Loop Detection". Its use in the
Request message records the path of LSRs the request has traversed. Label Request message records the path of LSRs the request has
Its use in the Label Mapping message records the path of LSRs a label traversed. Its use in the Label Mapping message records the path of
advertisement has traversed to setup an LSP. LSRs a label advertisement has traversed to setup an LSP.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Path Vector (0x0104) | Length | |0|0| Path Vector (0x0104) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 IP address (router-id) component of traversed. Each LSR Id is the IP address (router-id) component of
the LDP identifier for the corresponding LSR. This ensures it is the LDP identifier for the corresponding LSR. This ensures it is
unique within the LSR network. unique within the LSR network.
3.4.6.1. 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.
3.4.6.1.1. Label Request Path Vector 3.4.5.1.1. Label Request Path Vector
Section "Loop Detection" specifies situations when an LSR must Section "Loop Detection" specifies situations when an LSR must
include a Path Vector TLV in a Label Request message. include a Path Vector TLV in a Label Request message.
An LSR that receives a Path Vector in a Label Request message must An LSR that receives a Path Vector in a Label Request message must
perform the procedures described in Section "Loop Detection". perform the procedures described in Section "Loop Detection".
If the LSR detects a loop, it must reject the Label Request message. If the LSR detects a loop, it must reject the Label Request message.
The LSR must: The LSR must:
skipping to change at page 41, line 12 skipping to change at page 41, line 17
Note that a Label Request message with Path Vector TLV is forwarded Note that a Label Request message with Path Vector TLV is forwarded
until: until:
1. A loop is found, 1. A loop is found,
2. The LSP egress is reached, 2. The LSP egress is reached,
3. The maximum Path Vector limit or maximum Hop Count limit is 3. The maximum Path Vector limit or maximum Hop Count limit is
reached. This is treated as if a loop had been detected. reached. This is treated as if a loop had been detected.
3.4.6.1.2. Label Mapping Path Vector 3.4.5.1.2. Label Mapping Path Vector
Section "Loop Detection" specifies the situations when an LSR must Section "Loop Detection" specifies the situations when an LSR must
include a Path Vector TLV in a Label Mapping message. include a Path Vector TLV in a Label Mapping message.
An LSR that receives a Path Vector in a Label Mapping message must An LSR that receives a Path Vector in a Label Mapping message must
perform the procedures described in Section "Loop Detection". perform the procedures described in Section "Loop Detection".
If the LSR detects a loop, it must reject the Label Mapping message If the LSR detects a loop, it must reject the Label Mapping message
in order to prevent a forwarding loop. The LSR must: in order to prevent a forwarding loop. The LSR must:
skipping to change at page 41, line 42 skipping to change at page 42, line 5
Note that a Label Mapping message with a Path Vector TLV is forwarded Note that a Label Mapping message with a Path Vector TLV is forwarded
until: until:
1. A loop is found, 1. A loop is found,
2. An LSP ingress is reached, or 2. An LSP ingress is reached, or
3. The maximum Path Vector or maximum Hop Count limit is reached. 3. The maximum Path Vector or maximum Hop Count limit is reached.
This is treated as if a loop had been detected. This is treated as if a loop had been detected.
3.4.7. Status TLV 3.4.6. Status TLV
Notification messages carry Status TLVs to specify events being sig- Notification messages carry Status TLVs to specify events being
naled. signaled.
The encoding for the Status TLV is: The encoding for the Status TLV is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Status (0x0300) | Length | |0|0| Status (0x0300) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code | | Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Status Code Status Code
32-bit unsigned integer encoding the event being signaled. The 32-bit unsigned integer encoding the event being signaled. The
structure of a Status Code is: structure of a Status Code is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E|F| Status Data | |E|F| Status Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
E bit E bit
Fatal error bit. If set (=1), this is a fatal error notifica- Fatal error bit. If set (=1), this is a fatal error
tion. If clear (=0), this is an advisory notification. notification. If clear (=0), this is an advisory notification.
F bit F bit
Forward bit. If set (=1), the notification should be forwarded Forward bit. If set (=1), the notification should be forwarded
to the LSR for the next-hop or previous-hop for the LSP, if any, to the LSR for the next-hop or previous-hop for the LSP, if any,
associated with the event being signaled. If clear (=0), the associated with the event being signaled. If clear (=0), the
notification should not be forwarded. 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.
skipping to change at page 43, line 7 skipping to change at page 43, line 15
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 which
the Status TLV refers. If zero, no specific peer message is being the Status TLV refers. If zero, no specific peer message is being
identified. 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
messages. A message other than a Notification message may carry 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
set to 1 to indicate that the receiver should silently discard the 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
skipping to change at page 43, line 34 skipping to change at page 43, line 49
| | | |
+ + + +
| 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
sections following that define messages specify a value for the 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, Manda- Specifies the cumulative length in octets of the Message ID,
tory 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 response
to this message should include this Message Id in the notification to this message should include this Message Id in the notification
message; see Section "Notification Message". message; see Section "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.
skipping to change at page 44, line 35 skipping to change at page 45, line 15
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 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.
skipping to change at page 45, line 11 skipping to change at page 45, line 38
subtype that specifies a particular kind of message within that subtype that specifies a particular kind of message within that
class, this specification does not formalize the notion of a message class, this specification does not formalize the notion of a message
subtype. subtype.
The specification assigns type values for related messages, such as The specification assigns type values for related messages, such as
the label messages, from of a contiguous block in the 16-bit message the label messages, from of a contiguous block in the 16-bit message
type number space. type number space.
3.5.1. Notification Message 3.5.1. Notification Message
An LSR sends a Notification message to inform an LDP peer of a signi- An LSR sends a Notification message to inform an LDP peer of a
ficant event. A Notification message signals a fatal error or pro- significant event. A Notification message signals a fatal error or
vides advisory information such as the outcome of processing an LDP provides advisory information such as the outcome of processing an
message or the state of the LDP session. LDP message or the state of the LDP session.
The encoding for the Notification Message is: The encoding for the Notification Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| 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:
skipping to change at page 46, line 7 skipping to change at page 46, line 40
Extended Status 0x0301 4 See below Extended Status 0x0301 4 See below
Returned PDU 0x0302 var See below Returned PDU 0x0302 var See below
Returned Message 0x0303 var See below Returned Message 0x0303 var See below
Other Optional Parameters, specific to the particular event being Other Optional Parameters, specific to the particular event being
signaled by the Notification Messages may appear. These are signaled by the Notification Messages may appear. These are
described elsewhere. described elsewhere.
Extended Status Extended Status
The 4 octet value is an Extended Status Code that encodes addi- The 4 octet value is an Extended Status Code that encodes
tional information that supplements the status information con- additional information that supplements the status information
tained in the Notification Status Code. contained in the Notification Status Code.
Returned PDU Returned PDU
An LSR uses this parameter to return part of an LDP PDU to the An LSR uses this parameter to return part of an LDP PDU to the
LSR 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 signalled by the Notification message. condition being signalled 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
signalled by the Notification message. signalled 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 mes- advisory or error information it sends the peer a Notification
sage containing a Status TLV that encodes the information and option- message containing a Status TLV that encodes the information and
ally additional TLVs that provide more information about the event. optionally additional TLVs that provide more information about the
event.
If the condition is one that is a fatal error the Status Code carried If the condition is one that is a fatal error the Status Code carried
in the notification will indicate that. In this case, after sending in the notification will indicate that. In this case, after sending
the Notification message the LSR should terminate the LDP session by the Notification message the LSR should terminate the LDP session by
closing the session TCP connection and discard all state associated closing the session TCP connection and discard all state associated
with the session, including all label-FEC bindings learned via the with the session, including all label-FEC bindings learned via the
session. session.
When an LSR receives a Notification message that carries a Status When an LSR receives a Notification message that carries a Status
Code that indicates a fatal error, it should terminate the LDP ses- Code that indicates a fatal error, it should terminate the LDP
sion immediately by closing the session TCP connection and discard session immediately by closing the session TCP connection and discard
all state associated with the session, including all label-FEC bind- all state associated with the session, including all label-FEC
ings learned via the session. bindings learned via the session.
3.5.1.2. Events Signaled by Notification Messages 3.5.1.2. Events Signaled by Notification Messages
It is useful for descriptive purpose to classify events signaled by It is useful for descriptive purpose to classify events signaled by
Notification Messages into the following categories. Notification Messages into the following categories.
3.5.1.2.1. Malformed PDU or Message 3.5.1.2.1. Malformed PDU or Message
Malformed LDP PDUs or Messages that are part of the LDP Discovery Malformed LDP PDUs or Messages that are part of the LDP Discovery
mechanism are handled by silently discarding them. mechanism are handled by silently discarding them.
An LDP PDU received on a TCP connection for an LDP session is mal- An LDP PDU received on a TCP connection for an LDP session is
formed if: malformed if:
- The LDP Identifier in the PDU header is unknown to the receiver, - The LDP Identifier in the PDU header is unknown to the receiver,
or it is known but is not the LDP Identifier associated by the or it is known but is not the LDP Identifier associated by the
receiver with the LDP session. This is a fatal error signaled by receiver with the LDP peer for this LDP session. This is a fatal
the Bad LDP Identifier Status Code. 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 it
is supported but is not the version negotiated for the session is supported but is not the version negotiated for the session
during session establishment. This is a fatal error signaled by during session establishment. This is a fatal error signaled by
the Bad Protocol Version Status Code. the Bad Protocol Version Status Code.
- The PDU Length field is too short (< 18) or too long - 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 a If the Message Type is < 0x8000 (high order bit = 0) it is a
fatal error signaled by the Unknown Message Type Status Code. fatal 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 mes- - The Message Length is too large, that is, indicates that the
sage extends beyond the end of the containing LDP PDU. This is a message extends beyond the end of the containing LDP PDU. This
fatal error signaled by the Bad Message Length Status Code. is a fatal error signaled by the Bad Message Length 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:
skipping to change at page 48, line 18 skipping to change at page 49, line 5
- The TLV type is unknown. - The TLV type is unknown.
If the TLV type is < 0x8000 (high order bit 0) it is a fatal If the TLV type is < 0x8000 (high order bit 0) it is a fatal
error signaled by the Unknown TLV Status Code. error signaled by the Unknown TLV Status Code.
If the TLV type is >= 08000 (high order bit 1) the TLV is If the TLV type is >= 08000 (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 han- - The TLV Value is malformed. This occurs when the receiver
dles the TLV but cannot decode the TLV Value. This is inter- handles the TLV but cannot decode the TLV Value. This is
preted as indicative of a bug in either the sending or receiving interpreted as indicative of a bug in either the sending or
LSR. It is a fatal error signaled by the Malformed TLV Value receiving LSR. It is a fatal error signaled by the Malformed TLV
Status Code. Value Status Code.
3.5.1.2.3. Session Hold Timer Expiration 3.5.1.2.3. Session KeepAlive Timer Expiration
This is a fatal error signaled by the Hold Timer Expired Status Code. This is a fatal error signaled by the KeepAlive Timer Expired Status
Code.
3.5.1.2.4. Unilateral Session Shutdown 3.5.1.2.4. Unilateral Session Shutdown
This is a fatal event signaled by the Shutdown Status Code. The This is a fatal event signaled by the Shutdown Status Code. The
Notification Message may optionally include an Extended Status TLV to Notification Message may optionally include an Extended Status TLV to
provide a reason for the Shutdown. The sending LSR terminates the provide a reason for the Shutdown. The sending LSR terminates the
session immediately after sending the Notification. session immediately after sending the Notification.
3.5.1.2.5. Initialization Message Events 3.5.1.2.5. Initialization Message Events
The session initialization negotiation (see Section "Session Initial- The session initialization negotiation (see Section "Session
ization") may fail if the session parameters received in the Initial- Initialization") may fail if the session parameters received in the
ization Message are unacceptable. This is a fatal error. The Initialization Message are unacceptable. This is a fatal error. The
specific Status Code depends on the parameter deemed unacceptable, specific Status Code depends on the parameter deemed unacceptable,
and is defined in Sections "Initialization Message". and is defined in Sections "Initialization Message".
3.5.1.2.6. Events Resulting From Other Messages 3.5.1.2.6. Events Resulting From Other Messages
Messages other than the Initialization message may result in events Messages other than the Initialization message may result in events
that must be signaled to LDP peers via Notification Messages. These that must be signaled to LDP peers via Notification Messages. These
events and the Status Codes used in the Notification Messages to sig- events and the Status Codes used in the Notification Messages to
nal them are described in the sections that describe these messages. signal them are described in the sections that describe these
messages.
3.5.1.2.7. Miscellaneous Events 3.5.1.2.7. Miscellaneous Events
These are events that fall into none of the categories above. There These are events that fall into none of the categories above. There
are no miscellaneous events defined in this version of the protocol. are no miscellaneous events defined in this version of the protocol.
3.5.2. Hello Message 3.5.2. Hello Message
LDP Hello Messages are exchanged as part of the LDP Discovery Mechan- LDP Hello Messages are exchanged as part of the LDP Discovery
ism; see Section "LDP Discovery". Mechanism; see Section "LDP Discovery".
The encoding for the Hello Message is: The encoding for the Hello Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 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 Hellos
received from potential peers (see Section "Hello Message Pro- received from potential peers (see Section "Hello Message
cedures"). Hello Hold Time specifies the time the sending LSR Procedures"). Hello Hold Time specifies the time the sending LSR
will maintain its record of Hellos from the receiving LSR without will maintain its record of Hellos from the receiving LSR without
receipt of another Hello. 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 from
each other. Each proposes a hold time. The hold time used is each other. Each proposes a hold time. The hold time used is
the minimum of the hold times proposed in their Hellos. the minimum of the hold times proposed in their Hellos.
A value of 0 means use the default. There are interface type A value of 0 means use the default, which is 15 seconds for Link
specific defaults for Link Hellos as well as a default for Tar- Hellos and 45 seconds for Targeted Hellos. A value of 0xffff
geted Hellos. A value of 0xfffff means infinite. 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 Hel- A value of 1 requests the receiver to send periodic Targeted
los to the source of this Hello. A value of 0 makes no request. Hellos to the source of this Hello. A value of 0 makes no
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, the
receiving LSR checks whether it has been configured to send Tar- receiving LSR checks whether it has been configured to send
geted Hellos to the Hello source in response to Hellos with this Targeted Hellos to the Hello source in response to Hellos with
request. If not, it ignores the request. If so, it initiates this request. If not, it ignores the request. If so, it
periodic transmission of Targeted Hellos to the Hello source. initiates periodic transmission of Targeted Hellos to the Hello
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 ver- encoded as a TLV. The optional parameters defined by this
sion of the protocol are version of the protocol are
Optional Parameter Type Length Value Optional Parameter Type Length Value
Transport Address 0x0401 4 See below Transport Address 0x0401 4 See below
Configuration 0x0402 4 See below Configuration 0x0402 4 See below
Sequence Number Sequence Number
Transport Address Transport Address
Specifies the IPv4 address to be used for the sending LSR when Specifies the IPv4 address to be used for the sending LSR when
opening the LDP session TCP connection. If this optional TLV opening the LDP session TCP connection. If this optional TLV
is not present the IPv4 source address for the UDP packet car- is not present the IPv4 source address for the UDP packet
rying the Hello should be used. carrying the Hello should be used.
Configuration Sequence Number Configuration Sequence Number
Specifies a 4 octet unsigned configuration sequence number that Specifies a 4 octet unsigned configuration sequence number that
identifies the configuration state of the sending LSR. Used by identifies the configuration state of the sending LSR. Used by
the receiving LSR to detect configuration changes on the the receiving LSR to detect configuration changes on the
sending LSR. sending LSR.
3.5.2.1. Hello Message Procedures 3.5.2.1. Hello Message Procedures
An LSR receiving Hellos from another LSR maintains a Hello adjacency An LSR receiving Hellos from another LSR maintains a Hello adjacency
corresponding to the Hellos. The LSR maintains a hold timer with the corresponding to the Hellos. The LSR maintains a hold timer with the
Hello adjacency which it restarts whenever it receives a Hello that Hello adjacency which it restarts whenever it receives a Hello that
matches the Hello adjacency. If the hold timer for a Hello adjacency matches the Hello adjacency. If the hold timer for a Hello adjacency
expires the LSR discards the Hello adjacency: see sections "Maintain- expires the LSR discards the Hello adjacency: see sections
ing Hello Adjacencies" and "Maintaining LDP Sessions". "Maintaining Hello Adjacencies" and "Maintaining LDP Sessions".
We recommend that the interval between Hello transmissions be at most We recommend that the interval between Hello transmissions be at most
one third of the Hello hold time. one third of the Hello hold time.
An LSR processes a received LDP Hello as follows: An LSR processes a received LDP Hello as follows:
1. The LSR checks whether the Hello is acceptable. The criteria 1. The LSR checks whether the Hello is acceptable. The criteria
for determining whether a Hello is acceptable are implementa- for determining whether a Hello is acceptable are
tion dependent (see below for example criteria). implementation dependent (see below for example criteria).
2. If the Hello is not acceptable, the LSR ignores it. 2. If the Hello is not acceptable, the LSR ignores it.
3. If the Hello is acceptable, the LSR checks whether it has a 3. If the Hello is acceptable, the LSR checks whether it has a
Hello adjacency for the Hello source. If so, it restarts the Hello adjacency for the Hello source. If so, it restarts the
hold timer for the Hello adjacency. If not it creates a Hello hold timer for the Hello adjacency. If not it creates a Hello
adjacency for the Hello source and starts its hold timer. adjacency for the Hello source and starts its hold timer.
4. If the Hello carries any optional TLVs the LSR processes them 4. If the Hello carries any optional TLVs the LSR processes them
(see below). (see below).
5. Finally, if the LSR has no LDP session for the label space 5. Finally, if the LSR has no LDP session for the label space
specified by the LDP identifier in the PDU header for the specified by the LDP identifier in the PDU header for the
Hello, it follows the procedures of Section "LDP Session Estab- Hello, it follows the procedures of Section "LDP Session
lishment". Establishment".
The following are examples of acceptability criteria for Link and The following are examples of acceptability criteria for Link and
Targeted Hellos: Targeted Hellos:
A Link Hello is acceptable if the interface on which it was A Link Hello is acceptable if the interface on which it was
received has been configured for label switching. received has been configured for label switching.
A Targeted Hello from IP source address a.b.c.d is acceptable if A Targeted Hello from IP source address a.b.c.d is acceptable if
either: either:
skipping to change at page 52, line 18 skipping to change at page 53, line 11
a.b.c.d. a.b.c.d.
The following describes how an LSR processes Hello optional TLVs: The following describes how an LSR processes Hello optional TLVs:
Transport Address Transport Address
The LSR associates the specified transport address with the The LSR associates the specified transport address with the
Hello adjacency. Hello adjacency.
Configuration Sequence Number Configuration Sequence Number
The Configuration Sequence Number optional parameter is used by The Configuration Sequence Number optional parameter is used by
the sending LSR to signal configuration changes to the receiv- the sending LSR to signal configuration changes to the
ing LSR. When a receiving LSR playing the active role in LDP receiving LSR. When a receiving LSR playing the active role in
session establishment detects a change in the sending LSR con- LDP session establishment detects a change in the sending LSR
figuration, it may clear the session setup backoff delay, if configuration, it may clear the session setup backoff delay, if
any, associated with the sending LSR (see Section "Session Ini- any, associated with the sending LSR (see Section "Session
tialization"). Initialization").
A sending LSR using this optional parameter is responsible for A sending LSR using this optional parameter is responsible for
maintaining the configuration sequence number it transmits in maintaining the configuration sequence number it transmits in
Hello messages. Whenever there is a configuration change on Hello messages. Whenever there is a configuration change on
the sending LSR, it increments the configuration sequence the sending LSR, it increments the configuration sequence
number. number.
3.5.3. Initialization Message 3.5.3. Initialization Message
The LDP Initialization Message is exchanged as part of the LDP ses- The LDP Initialization Message is exchanged as part of the LDP
sion establishment procedure; see Section "LDP Session Establish- session establishment procedure; see Section "LDP Session
ment". Establishment".
The encoding for the Initialization Message is: The encoding for the Initialization Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| 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 common Specifies values proposed by the sending LSR for parameters that
to all LDP sessions. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Common Sess Parms (0x0500)| Length | |0|0| Common Sess Parms (0x0500)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Version | Hold Time | | Protocol Version | KeepAlive Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|D| Reserved | PVLim | Max PDU Length | |A|D| Reserved | PVLim | Max PDU Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver LDP Identifer | | Receiver LDP Identifer |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++ -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
Protocol Version Protocol Version
Two octet unsigned integer containing the version number of the Two octet unsigned integer containing the version number of the
protocol. This version of the specification specifies LDP pro- protocol. This version of the specification specifies LDP
tocol version 1. protocol version 1.
Hold 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 Interval. The receiving LSR MUST calculate the value KeepAlive Time. The receiving LSR MUST calculate the value of
of the KeepAlive Timer by using the smaller of its proposed the KeepAlive Timer by using the smaller of its proposed
Hold Time and the Hold Time received in the PDU. The value KeepAlive Time and the KeepAlive Time received in the PDU. The
chosen for Hold Time indicates the maximum number of seconds value chosen for KeepAlive Time indicates the maximum number of
that may elapse between the receipt of successive PDUs from the seconds that may elapse between the receipt of successive PDUs
LDP peer. The KeepAlive Timer is reset each time a PDU from the LDP peer. The KeepAlive Timer is reset each time a
arrives. PDU arrives.
A, Label Advertisement Discipline A, Label Advertisement Discipline
Indicates the type of Label advertisement. A value of 0 means Indicates the type of Label advertisement. A value of 0 means
Downstream Unsolicited advertisement; a value of 1 means Down- Downstream Unsolicited advertisement; a value of 1 means
stream On Demand. Downstream On Demand.
If one LSR proposes Downstream Unsolicted and the other pro- If one LSR proposes Downstream Unsolicted and the other
poses 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 must be used. Demand must be used.
- Otherwise, Downstream Unsolicted must be used. - Otherwise, Downstream Unsolicted 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
skipping to change at page 54, line 24 skipping to change at page 55, line 20
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 pro- detection is disabled (D = 0). If the loop detection
cedures 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 configured with the same path vector limit. Although
knowledege of a peer's path vector limit will not change an knowledege of a peer's path vector limit will not change an
LSR's behavior, it does enable the LSR to alert an operator to LSR's behavior, it does enable the LSR to alert an operator to
a possible misconfiguration. a possible misconfiguration.
skipping to change at page 55, line 10 skipping to change at page 56, line 6
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 Identifer Receiver LDP Identifer
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 Pro- one of its Hello adjacencies; see Section "Hello Message
cedures". Procedures".
If there is no matching Hello adjacency, the LSR must send a If there is no matching Hello adjacency, the LSR must send a
Session Rejected/No Hello Notification message in response to Session Rejected/No Hello Notification message in response to
the Initialization message and not establish the session. the Initialization message and not establish the session.
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are: encoded as a TLV. The optional parameters are:
Optional Parameter Type Length Value Optional Parameter Type Length Value
skipping to change at page 55, line 34 skipping to change at page 56, line 30
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 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 follow- Specifies the merge capabilities of an ATM switch. The
ing values are supported in this version of the specification: following values are supported in this version of the
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
skipping to change at page 56, line 22 skipping to change at page 57, line 19
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-VP-merge-capable switches is a subject for future non-VP-merge-capable switches is a subject for future
study. study.
Note that if VP merge is used, it is the responsibility of the Note that if VP merge is used, it is the responsibility of the
ingress node to ensure that the chosen VCI is unique within the ingress node to ensure that the chosen VCI is unique within the
LSR domain. LSR domain (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 direc- VPI) a given VCI may appear in a label mapping for one
tion on the link only. When either or both of the peers speci- direction on the link only. When either or both of the peers
fies unidirectional VC capability, both LSRs use unidirectional specifies unidirectional VC capability, both LSRs use
VC label assignement for the link as follows. The LSRs compare unidirectional VC label assignement for the link as follows.
their LDP Identifiers as unsigned integers. The LSR with the The LSRs compare their LDP Identifiers as unsigned integers.
larger LDP Identifier may assign only odd-numbered VCIs in the The LSR with the larger LDP Identifier may assign only odd-
VPI/VCI range as labels. The system with the smaller LDP Iden- numbered VCIs in the VPI/VCI range as labels. The system with
tifier may assign only even-numbered VCIs in the VPI/VCI range the smaller LDP Identifier may assign only even-numbered VCIs
as labels. in the VPI/VCI range as labels.
Reserved Reserved
This field is reserved. It must be set to zero on transmission This field is reserved. It must be set to zero on transmission
and ignored on receipt. and ignored on receipt.
One or more ATM Label Range Components One or more ATM Label Range Components
A list of ATM Label Range Components which together specify the A list of ATM Label Range Components 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 neigh- accept labels. LSRs MUST NOT establish a session with
bors for which the intersection of ranges is NULL. In this neighbors for which the intersection of ranges is NULL. In
case, the LSR must send a Session Rejected/Parameters Label this case, the LSR must send a Session Rejected/Parameters
Range Notification message in response to the Initialization Label Range Notification message in response to the
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 transmis- This field is reserved. It must be set to zero on
sion and must be ignored on receipt. transmission and must be ignored on receipt.
Minimum VPI (12 bits) Minimum VPI (12 bits)
This 12 bit field specifies the lower bound of a block of This 12 bit field specifies the lower bound of a block of
Virtual Path Identifiers that is supported on the originating Virtual Path Identifiers that is supported on the originating
switch. If the VPI is less than 12-bits it should be right switch. If the VPI is less than 12-bits it should be right
justified in this field and preceding bits should be set to justified in this field and preceding bits should be set to
0. 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 ori- Virtual Connection Identifiers that is supported on the
ginating switch. If the VCI is less than 16-bits it should originating switch. If the VCI is less than 16-bits it
be right justified in this field and preceding bits should be should be right justified in this field and preceding bits
set to 0. should be set to 0.
Maximum 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 originating
switch. If the VPI is less than 12-bits it should be right switch. If the VPI is less than 12-bits it should be right
justified in this field and preceding bits should be set to justified in this field and preceding bits should be set to
0. 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 ori- Virtual Connection Identifiers that is supported on the
ginating switch. If the VCI is less than 16-bits it should originating switch. If the VCI is less than 16-bits it
be right justified in this field and preceding bits should be should be right justified in this field and preceding bits
set to 0. should be set to 0.
See [ATM-VP] for specification of the fields for ATM Label Range
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 Relay
link to specify Frame Relay-specific session parameters. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| FR Sess Parms (0x0502) | Length | |0|0| FR Sess Parms (0x0502) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M | N | 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 specifi- following values are supported in this version of the
cation: specification:
Value Meaning Value Meaning
0 Merge not supported 0 Merge not supported
1 Merge supported 1 Merge supported
Non-merge and merge Frame Relay LSRs may freely interoperate. Non-merge and merge Frame Relay LSRs may freely interoperate.
N, Number of label range components 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
A value of 0 specifies bidirectional VC capability, meaning the
LSR can support the use of a given DLCI as a label for both
link directions independently. A value of 1 specifies
unidirectional VC capability, meaning a given DLCI may appear
in a label mapping for one direction on the link only. When
either or both of the peers specifies unidirectional VC
capability, both LSRs use unidirectional VC label assignement
for the link as follows. The LSRs compare their LDP
Identifiers as unsigned integers. The LSR with the larger LDP
Identifier may assign only odd-numbered DLCIs in the range as
labels. The system with the smaller LDP Identifier may assign
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 inter- received range and its own supported label range. The
section is the range in which the LSR may allocate and accept intersection is the range in which the LSR may allocate and
labels. LSRs MUST NOT establish a session with neighbors for accept labels. LSRs MUST NOT establish a session with
which the intersection of ranges is NULL. In this case, the neighbors for which the intersection of ranges is NULL. In
LSR must send a Session Rejected/Parameters Label Range Notifi- this case, the LSR must send a Session Rejected/Parameters
cation message in response to the Initialization message and Label Range Notification message in response to the
not establish the session. Initialization message and not establish the session.
The encoding for a Frame Relay Label Range Component is: The encoding for a Frame Relay Label Range Component is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Len| Minimum DLCI | | Reserved |Len| Minimum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Maximum DLCI | | Reserved | Maximum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved Reserved
This field is reserved. It must be set to zero on transmis- This field is reserved. It must be set to zero on
sion 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
1 17 1 17
2 23 2 23
skipping to change at page 60, line 8 skipping to change at page 61, line 22
Data Link Connection Identifiers (DLCIs) that is supported on Data Link Connection Identifiers (DLCIs) that is supported on
the originating switch. The DLCI should be right justified the originating switch. The DLCI should be right justified
in this field and unused bits should be set to 0. 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 Ini- "Session Initialization" for general procedures for handling the
tialization Message. Initialization Message.
3.5.4. KeepAlive Message 3.5.4. KeepAlive Message
An LSR sends KeepAlive Messages as part of a mechanism that monitors An LSR sends KeepAlive Messages as part of a mechanism that monitors
the integrity of the LDP session transport connection. the integrity of the LDP session transport connection.
The encoding for the KeepAlive Message is: The encoding for the KeepAlive Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| 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 Hold Timer mechanism described in Section "Maintaining LDP Ses- The KeepAlive Timer mechanism described in Section "Maintaining LDP
sions" resets a session hold timer every time an LDP PDU is received. Sessions" resets a session KeepAlive timer every time an LDP PDU is
The KeepAlive Message is provided to allow reset of the Hold Timer in received. The KeepAlive Message is provided to allow reset of the
circumstances where an LSR has no other information to communicate to KeepAlive Timer in circumstances where an LSR has no other
an LDP peer. information to communicate to an LDP peer.
An LSR must arrange that its peer receive an LDP Message from it at An LSR must arrange that its peer receive an LDP Message from it at
least every Hold Time period. Any LDP protocol message will do but, least every KeepAlive Time period. Any LDP protocol message will do
in circumstances where no other LDP protocol messages have been sent but, in circumstances where no other LDP protocol messages have been
within the period, a KeepAlive message must be sent. sent within the period, a KeepAlive message must be sent.
3.5.5. Address Message 3.5.5. Address Message
An LSR sends the Address Message to an LDP peer to advertise its An LSR sends the Address Message to an LDP peer to advertise its
interface addresses. interface addresses.
The encoding for the Address Message is: The encoding for the Address Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Address (0x0300) | Message Length | |0| Address (0x0300) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Address List TLV | | Address List TLV |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
Address List TLV Address List TLV
The list of interface addresses being 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 Identif- learns to maintain a database for mapping between peer LDP
iers and next hop addresses; see Section "LDP Identifiers and Next Identifiers and next hop addresses; see Section "LDP Identifiers and
Hop Addresses". Next Hop Addresses".
When a new LDP session is initialized and before sending Label Map- When a new LDP session is initialized and before sending Label
ping or Label Request messages an LSR should advertise its interface Mapping or Label Request messages an LSR should advertise its
addresses with one or more Address messages. interface addresses with one or more Address messages.
Whenever an LSR "activates" a new interface address, it should adver- Whenever an LSR "activates" a new interface address, it should
tise the new address with an Address message. advertise the new address with an Address message.
Whenever an LSR "de-activates" a previously advertised address, it Whenever an LSR "de-activates" a previously advertised address, it
should withdraw the address with an Address Withdraw message; see should withdraw the address with an Address Withdraw message; see
Section "Address Withdraw Message". Section "Address Withdraw Message".
3.5.6. Address Withdraw Message 3.5.6. Address Withdraw Message
An LSR sends the Address Message to an LDP peer to withdraw previ- An LSR sends the Address Withdraw Message to an LDP peer to withdraw
ously advertised interface addresses. previously advertised interface addresses.
The encoding for the Address Withdraw Message is: The encoding for the Address Withdraw Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U Address Withdraw (0x0301) | Message Length | |0| Address Withdraw (0x0301) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Address List TLV | | Address List TLV |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
Address list TLV Address list TLV
The list of interface addresses being withdrawn by the sending LSR. The list of interface addresses being withdrawn by the sending LSR.
The encoding for the Address list TLV is specified in Section 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 Withdraw mes- No optional parameters are defined for the Address Withdraw
sage. message.
3.5.6.1. Address Withdraw Message Procedures 3.5.6.1. Address Withdraw Message Procedures
See Section "Address Message Procedures" See Section "Address Message Procedures"
3.5.7. Label Mapping Message 3.5.7. Label Mapping Message
An LSR sends a Label Mapping message to an LDP peer to advertise 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.
The encoding for the Label Mapping Message is: The encoding for the Label Mapping Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Label Mapping (0x0400) | Message Length | |0| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV | | Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
FEC TLV FEC TLV
Specifies the FEC component of the FEC-Label mapping being adver- Specifies the FEC component of the FEC-Label mapping being
tised. See Section "FEC TLV" for encoding. advertised. See Section "FEC TLV" for encoding.
Label TLV Label TLV
Specifies the Label component of the FEC-Label mapping. See Sec- Specifies the Label component of the FEC-Label mapping. See
tion "Label TLV" for encoding. Section "Label TLV" for encoding.
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are: encoded as a TLV. The optional parameters are:
Optional Parameter Length Value Optional Parameter Length Value
Label Request 4 See below Label Request 4 See below
Message Id TLV Message ID TLV
COS TLV 1 See below
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 COS, Hop Count, and Path Vector TLVs can be The encodings for the Hop Count, and Path Vector TLVs can be found
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 that carried the Return Message Id optional parameter message it must include the Request Message Id optional
(see Section "Label Request Message") the Label Mapping message parameter. The value of this optional parameter is the Message
must include the Request Message Id optional parameter. The Id of the corresponding Label Request Message.
value of this optional parameter is the Message Id of the
corresponding Label Request Message.
COS
Specifies the Class of Service (COS) to be associated with the
FEC-Label mapping. If not present, the LSR should use its
default COS for IP packets as the COS.
Hop Count Hop Count
Specifies the running total of the number of LSR hops along the Specifies the running total of the number of LSR hops along the
LSP being setup by the Label Message. Section "Hop Count Pro- LSP being setup by the Label Message. Section "Hop Count
cedures" describes how to handle this TLV. Procedures" describes how to handle this TLV.
Path Vector Path Vector
Specifies the LSRs along the LSP being setup by the Label Mes- Specifies the LSRs along the LSP being setup by the Label
sage. Section "Path Vector Procedures" describes how to handle Message. Section "Path Vector Procedures" describes how to
this TLV. handle this TLV.
3.5.7.1. Label Mapping Message Procedures 3.5.7.1. Label Mapping Message Procedures
The Mapping message is used by an LSR to distribute a label mapping The Mapping message is used by an LSR to distribute a label mapping
for a FEC to an LDP peer. If an LSR distributes a mapping for a FEC for a FEC to an LDP peer. If an LSR distributes a mapping for a FEC
to multiple LDP peers, it is a local matter whether it maps a single to multiple LDP peers, it is a local matter whether it maps a single
label to the FEC, and distributes that mapping to all its peers, or label to the FEC, and distributes that mapping to all its peers, or
whether it uses a different mapping for each of its peers. whether it uses a different mapping for each of its peers.
An LSR is responsible for the consistency of the label map- pings it An LSR is responsible for the consistency of the label mappings it
has distributed, and that its peers have these mappings. has distributed, and that its peers have these mappings.
An LSR receiving a Label Mapping message from a downstream LSR for a
Prefix or Host Address FEC Element should not use the label for
forwarding unless its routing table contains an entry that exactly
matches the FEC Element.
See Appendx A "LDP Label Distribution Procedures" for more details. See Appendx A "LDP Label Distribution Procedures" for more details.
3.5.7.1.1. Independent Control Mapping 3.5.7.1.1. Independent Control Mapping
If an LSR is configured for independent control, a mapping message is If an LSR is configured for independent control, a mapping message is
transmitted by the LSR upon any of the following conditions: transmitted by the LSR upon any of the following conditions:
1. The LSR recognizes a new FEC via the forwarding table, and the 1. The LSR recognizes a new FEC via the forwarding table, and the
label advertisement mode is Downstream Unsolicited advertise- label advertisement mode is Downstream Unsolicited
ment. advertisement.
2. The LSR receives a Request message from an upstream peer for a 2. The LSR receives a Request message from an upstream peer for a
FEC present in the LSR's forwarding table. FEC present in the LSR's forwarding table.
3. The next hop for a FEC changes to another LDP peer, and loop 3. The next hop for a FEC changes to another LDP peer, and loop
detection is configured. detection is configured.
4. The attributes of a mapping change. 4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND 5. The receipt of a mapping from the downstream next hop AND
skipping to change at page 65, line 42 skipping to change at page 66, line 46
4. The attributes of a mapping change. 4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND 5. The receipt of a mapping from the downstream next hop AND
a) no upstream mapping has been created OR a) no upstream mapping has been created OR
b) loop detection is configured OR b) loop detection is configured OR
c) the attributes of the mapping have changed. c) the attributes of the mapping have changed.
3.5.7.1.3. Downstream on Demand Label Advertisement 3.5.7.1.3. Downstream on Demand Label Advertisement
In general, the upstream LSR is responsible for requesting label map- In general, the upstream LSR is responsible for requesting label
pings when operating in Downstream on Demand mode. However, unless mappings when operating in Downstream on Demand mode. However,
some rules are followed, it is possible for neighboring LSRs with unless some rules are followed, it is possible for neighboring LSRs
different advertisement modes to get into a livelock situation where with different advertisement modes to get into a livelock situation
everything is functioning properly, but no labels are distributed. where everything is functioning properly, but no labels are
For example, consider two LSRs Ru and Rd where Ru is the upstream LSR distributed. For example, consider two LSRs Ru and Rd where Ru is
and Rd is the downstream LSR for a particular FEC. In this example, the upstream LSR and Rd is the downstream LSR for a particular FEC.
Ru is using Downstream Unsolicited advertisement mode and Rd is using In this example, Ru is using Downstream Unsolicited advertisement
Downstream on Demand mode. In this case, Rd may assume that Ru will mode and Rd is using Downstream on Demand mode. In this case, Rd may
request a label mapping when it wants one and Ru may assume that Rd assume that Ru will request a label mapping when it wants one and Ru
will advertise a label if it wants Ru to use one. If Rd and Ru may assume that Rd will advertise a label if it wants Ru to use one.
operate as suggested, no labels will be distributed from Rd to Ru. If Rd and Ru operate as suggested, no labels will be distributed from
Rd to Ru.
This livelock situation can be avoided if the following rule is This livelock situation can be avoided if the following rule is
observed: an LSR operating in Downstream on Demand mode should not be observed: an LSR operating in Downstream on Demand mode should not be
expected to send unsolicited mapping advertisements. Therefore, if expected to send unsolicited mapping advertisements. Therefore, if
the downstream LSR is operating in Downstream on Demand mode, the the downstream LSR is operating in Downstream on Demand mode, the
upstream LSR is responsible for requesting label mappings as needed. upstream LSR is responsible for requesting label mappings as needed.
3.5.7.1.4. Downstream Unsolicited Label Advertisement 3.5.7.1.4. Downstream Unsolicited Label Advertisement
In general, the downstream LSR is responsible for advertising a label In general, the downstream LSR is responsible for advertising a label
mapping when it wants an upstream LSR to use the label. An upstream mapping when it wants an upstream LSR to use the label. An upstream
LSR may issue a mapping request if it so desires. LSR may issue a mapping request if it so desires.
The combination of Downstream Unsolicited mode and conservative label
retention can lead to a situation where an LSR releases the label for
a FEC that it later needs. For example, if LSR Rd advertises to LSR
Ru the label for a FEC for which it is not Ru's next hop, Ru will
release the label. If Ru's next hop for the FEC later changes to Rd,
it needs the previously released label.
To deal with this situation either Ru can explicitly request the
label when it needs it, or Rd can periodically readvertise it to Ru.
In many situations Ru will know when it needs the label from Rd. For
example, when its next hop for the FEC changes to Rd. However, there
could be situations when Ru does not. For example, Rd may be
attempting to establish an LSP with non-standard properties. Forcing
Ru to explicitly request the label in this situation would require it
to maintain state about a potential LSP with non-standard properties.
In situations where Ru knows it needs the label, it is responsible
for explicitly requesting the label by means of a Label Request
message. In situations where Ru may not know that it needs the
label, Rd is responsible for periodically readvertising the label to
Ru.
For this version of LDP, the only situation where Ru knows it needs a
label for a FEC from Rd is when Rd is its next hop for the FEC, Ru
does not have a label from Rd, and the LSP for the FEC is one that
can be established with TLVs defined in this document.
3.5.8. Label Request Message 3.5.8. Label Request Message
An LSR sends the Label Request Message to an LDP peer to request a An LSR sends the Label Request Message to an LDP peer to request a
binding (mapping) for a FEC. binding (mapping) for a FEC.
The encoding for the Label Request Message is: The encoding for the Label Request Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| 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
Return Message Id TLV 0 See below
COS TLV 1 See below
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 COS, Hop Count, and Path Vector TLVs can be The encodings for the Hop Count, and Path Vector TLVs can be found
found in Section "TLV Encodings for Commonly Used Parameters". in Section "TLV Encodings for Commonly Used Parameters".
Return Message Id
Requests the LDP peer include the Message Id of this Label
Request message in its Label Mapping message response. If an
LDP peer receives a Label Request message with the Return Mes-
sage Id optional parameter, its Label Mapping message response
must contain a Label Request Message Id optional parameter with
the Message Id of the Label Request message. See Section
"Label Mapping Message".
COS
Specifies the Class of Service (COS) to be associated with the
requested FEC-Label mapping. If not present, the LSR should
use its default COS for IP packets as the COS.
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 con- An LSR may transmit a Request message under any of the following
ditions: conditions:
1. The LSR recognizes a new FEC via the forwarding table, and the 1. The LSR recognizes a new FEC via the forwarding table, and the
next hop is an LDP peer, and the LSR doesn't already have a next hop is an LDP peer, and the LSR doesn't already have a
mapping from the next hop for the given FEC. mapping from the next hop for the given FEC.
2. The next hop to the FEC changes, and the LSR doesn't already 2. The next hop to the FEC changes, and the LSR doesn't already
have a mapping from that next hop for the given FEC. have a mapping from that next hop for the given FEC.
Note that if the LSR already has a pending Label Request
message for the new hext hop it should not issue an additional
Label Request in response to the next hop change.
3. The LSR receives a Label Request for a FEC from an upstream LDP 3. The LSR receives a Label Request for a FEC from an upstream LDP
peer, the FEC next hop is an LDP peer, and the LSR doesn't peer, the FEC next hop is an LDP peer, and the LSR doesn't
already have a mapping from the next hop. already have a mapping from the next hop.
Note that since a non-merge LSR must setup a separate LSP for
each upstream peer requesting a label, it must send a separate
Label Request for each such peer. A consequence of this is
that a non-merge LSR may have multiple Label Request messages
for a given FEC outstanding at the same time.
The receiving LSR should respond to a Label Request message with a The receiving LSR should respond to a Label Request message with a
Label Mapping for the requested label or with a Notification message Label Mapping for the requested label or with a Notification message
indicating why it cannot satisfy the request. indicating why it cannot satisfy the request.
When the FEC for which a label is requested is a Prefix FEC Element
or a Host Address FEC Element, the receiving LSR uses its routing
table to determine its response. Unless its routing table includes
an entry that exactly matches the requested Prefix or Host Address,
the LSR must respond with a No Route Notification message.
The message ID of the Label Request message serves as an identifier
for the Label Request transaction. When the receiving LSR responds
with a Label Mapping message, the mapping message must include a
Label Request/Returned Message ID TLV optional parameter which
includes the message ID of the Label Request message. Note that
since LSRs use Label Request message IDs as transaction identifiers
an LSR should not reuse the message ID of a Label Request message
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 request- When resources become available the LSR must notify the
ing 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 Resources
Available Status code. Available Status code.
Loop Detected Loop Detected
The LSR has detected a looping Label Requst message. The LSR has detected a looping Label Requst message.
See Appendx A "LDP Label Distribution Procedures" for more details. See Appendx A "LDP Label Distribution Procedures" for more details.
3.5.9. Label Withdraw Message 3.5.9. Label Abort Request Message
The Label Abort Request message may be used to abort an outstanding
Label Request message.
The encoding for the Label Abort Request Message is:
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| Label Abort Req (0x0402) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Request Message ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID
32-bit value used to identify this message.
FEC TLV
Identifies the FEC for which the FEC-label mapping is being
withdrawn.
Label Request Message ID TLV
Specifies the message ID of the Label Request message to be
aborted.
3.5.9.1. Label Abort Request Message Procedures
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
following circumstances:
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
Abort Request for FEC from an upstream peer Y.
3. Ru is a merge, non-ingress LSR and has received a Label Abort
Request for FEC from an upstream peer Y and Y is the only
(last) upstream LSR requesting a label for FEC.
There may be other situations where an LSR may choose to abort an
outstanding Label Request message in order to reclaim resource
associated with the pending LSP. However, specificaion of general
strategies for using the abort mechanism is beyond the scope of LDP.
When an LSR receives a Label Abort Request message, if it has not
previously responded to the Label Request being aborted with a Label
Mapping message or some other Notification message, it must
acknowledge the abort by responding with a Label Request Aborted
Notification message. The Notification must include a Label Request
Message ID TLV that carries the message ID of the aborted Label
Request message.
If an LSR receives a Label Abort Request Message after it has
responded to the Label Request in question with a Label Mapping
message or a Notification message, it ignores the abort request.
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
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
Label Release mesage.
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
from its peer:
- A Label Request Aborted Notfication message acknowledging the
abort;
- A Label Mapping message in response to the Label Request message
being aborted;
- A Notification message in response to the Label Request message
being aborted (e.g., Loop Detected, No Label Resources, etc.).
To protect itself against tardy peers or faulty peer implementations
an LSR may choose to time out receipt of the above. The time out
period should be relatively long (several minutes).
Note that the response to a Label Abort Request message is never
"ordered". That is, the response does not depend on the downstream
state of the LSP setup being aborted. An LSR receiving a Label Abort
Request message must process it immediately, regardless of the
downstream state of the LSP, responding with a Label Request Aborted
Notification or ignoring it, as appropriate.
3.5.10. Label Withdraw Message
An LSR sends a Label Withdraw Message to an LDP peer to signal the An LSR sends a Label Withdraw Message to an LDP peer to signal the
peer that the peer may not continue to use specific FEC-label map- peer that the peer may not continue to use specific FEC-label
pings the LSR had previously advertised. This breaks the mapping mappings the LSR had previously advertised. This breaks the mapping
between the FECs and the labels. between the FECs and the labels.
The encoding for the Label Withdraw Message is: The encoding for the Label Withdraw Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Label Withdraw (0x0402) | Message Length | |0| Label Withdraw (0x0402) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) | | Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message ID
32-bit value used to identify this message. 32-bit value used to identify this message.
FEC TLV FEC TLV
Identifies the FEC for which the FEC-label mapping is being with- Identifies the FEC for which the FEC-label mapping is being
drawn. withdrawn.
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are: encoded as a TLV. The optional parameters are:
Optional Parameter Length Value Optional Parameter Length Value
Label TLV variable See below Label TLV variable See below
The encoding for Label TLVs are found in Section "Label TLVs". The encoding for Label TLVs are found in Section "Label TLVs".
Label Label
If present, specifies the label being withdrawn (see procedures If present, specifies the label being withdrawn (see procedures
below). below).
3.5.9.1. Label Withdraw Message Procedures 3.5.10.1. Label Withdraw Message Procedures
An LSR transmits a Label Withdraw message under the following condi- An LSR transmits a Label Withdraw message under the following
tions: conditions:
1. The LSR no longer recognizes a previously known FEC. 1. The LSR no longer recognizes a previously known FEC for which
it has advertised a label.
2. The LSR has decided unilaterally (e.g., via configuration) to 2. The LSR has decided unilaterally (e.g., via configuration) to
no longer label switch a FEC (or FECs) with the label mapping no longer label switch a FEC (or FECs) with the label mapping
being withdrawn. being withdrawn.
The FEC TLV specifies the FEC for which labels are to be withdrawn. The FEC TLV specifies the FEC for which labels are to be withdrawn.
If no Label TLV follows the FEC, all labels associated with the FEC If no Label TLV follows the FEC, all labels associated with the FEC
are to be withdrawn; otherwise only the label specified in the are to be withdrawn; otherwise only the label specified in the
optional Label TLV is to be withdrawn. optional Label TLV is to be withdrawn.
The FEC TLV may contain the Wildcard FEC Element; if so, it may con- The FEC TLV may contain the Wildcard FEC Element; if so, it may
tain no other FEC Elements. In this case, if the Label Withdraw mes- contain no other FEC Elements. In this case, if the Label Withdraw
sage contains an optional Label TLV, then the label is to be with- message contains an optional Label TLV, then the label is to be
drawn from all FECs to which it is bound. If there is not an withdrawn from all FECs to which it is bound. If there is not an
optional Label TLV in the Label Withdraw message, then the sending optional Label TLV in the Label Withdraw message, then the sending
LSR is withdrawing all label mappings previously advertised to the LSR is withdrawing all label mappings previously advertised to the
receiving LSR. receiving LSR.
An LSR that receives a Label Withdraw message must respond with a
Label Release message.
See Appendx A "LDP Label Distribution Procedures" for more details. See Appendx A "LDP Label Distribution Procedures" for more details.
3.5.10. Label Release Message 3.5.11. Label Release Message
An LSR sends a Label Release message to an LDP peer to signal the An LSR sends a Label Release message to an LDP peer to signal the
peer that the LSR no longer needs specific FEC-label mappings previ- peer that the LSR no longer needs specific FEC-label mappings
ously requested of and/or advertised by the peer. previously requested of and/or advertised by the peer.
The encoding for the Label Release Message is: The encoding for the Label Release Message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Label Release (0x0403) | Message Length | |0| Label Release (0x0403) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) | | Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:
skipping to change at page 71, line 4 skipping to change at page 74, line 37
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).
3.5.10.1. 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 follow- An LSR must transmit a Label Release message under any of the
ing conditions: following conditions:
1. The LSR which sent the label mapping is no longer the next hop 1. The LSR which sent the label mapping is no longer the next hop
for the mapped FEC, and the LSR is configured for conservative for the mapped FEC, and the LSR is configured for conservative
operation. operation.
2. The LSR receives a label mapping from an LSR which is not the 2. The LSR receives a label mapping from an LSR which is not the
next hop for the FEC, and the LSR is configured for conserva- next hop for the FEC, and the LSR is configured for
tive operation. conservative operation.
3. The LSR has received a Label Withdraw message for a previously 3. The LSR receives a Label Withdraw message.
received label.
Note that if an LSR is configured for "liberal mode", a release mes- Note that if an LSR is configured for "liberal mode", a release
sage will never be transmitted in the case of conditions (1) and (2) message will never be transmitted in the case of conditions (1) and
as specified above. In this case, the upstream LSR keeps each unused (2) as specified above. In this case, the upstream LSR keeps each
label, so that it can immediately be used later if the downstream unused label, so that it can immediately be used later if the
peer becomes the next hop for the FEC. downstream peer becomes the next hop for the FEC.
The FEC TLV specifies the FEC for which labels are to be released. The FEC TLV specifies the FEC for which labels are to be released.
If no Label TLV follows the FEC, all labels associated with the FEC If no Label TLV follows the FEC, all labels associated with the FEC
are to be released; otherwise only the label specified in the are to be released; otherwise only the label specified in the
optional Label TLV is to be released. optional Label TLV is to be released.
The FEC TLV may contain the Wildcard FEC Element; if so, it may con- The FEC TLV may contain the Wildcard FEC Element; if so, it may
tain no other FEC Elements. In this case, if the Label Release mes- contain no other FEC Elements. In this case, if the Label Release
sage contains an optional Label TLV, then the label is to be released message contains an optional Label TLV, then the label is to be
for all FECs to which it is bound. If there is not an optional Label released for all FECs to which it is bound. If there is not an
TLV in the Label Release message, then the sending LSR is releasing optional Label TLV in the Label Release message, then the sending LSR
all label mappings previously learned from the receiving LSR. is releasing all label mappings previously learned from the receiving
LSR.
See Appendx A "LDP Label Distribution Procedures" for more details. See Appendx A "LDP Label Distribution Procedures" for more details.
3.6. Messages and TLVs for Extensibility 3.6. Messages and TLVs for Extensibility
Support for LDP extensibility includes the rules for the U and F bits Support for LDP extensibility includes the rules for the U and F bits
that specify how an LSR should handle unknown TLVs and messages. that specify how an LSR should handle unknown TLVs and messages.
This section specifies TLVs and messages for vendor-private and This section specifies TLVs and messages for vendor-private and
experimental use. experimental use.
3.6.1. LDP Vendor-private Extensions 3.6.1. LDP Vendor-private Extensions
Vendor-private TLVs and messages are used to convey vendor-private Vendor-private TLVs and messages are used to convey vendor-private
information between LSRs. information between LSRs.
3.6.1.1. LDP Vendor-private TLVs 3.6.1.1. LDP Vendor-private TLVs
The Type range 0x2F00 through 0x2FFF is reserved for vendor-private The Type range 0x3E00 through 0x3EFF is reserved for vendor-private
TLVs. TLVs.
The encoding for a vendor-private TLV is: The encoding for a vendor-private TLV is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type (0x2F00-0x2FFF) | Length | |U|F| Type (0x3E00-0x3EFF) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 and
the entire message must be ignored; if U is set (=1), the unknown the entire message must be ignored; if U is set (=1), the unknown
TLV is silently ignored and the rest of the message is processed as TLV is silently ignored and the rest of the message is processed as
if the unknown TLV did not exist. if the unknown TLV did not exist.
The determination as to whether a vendor-private message is under- The determination as to whether a vendor-private message is
stood is based on the Type and the mandatory Vendor ID field. understood is based on the Type and the mandatory Vendor ID field.
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 TLF is is to be for- set and the LDP message containing the unknown TLF is is to be
warded. If F is clear (=0), the unknown TLV is not forwarded with forwarded. If F is clear (=0), the unknown TLV is not forwarded
the containing message; if F is set (=1), the unknown TLV is for- with the containing message; if F is set (=1), the unknown TLV is
warded with the containing message. forwarded with the containing message.
Type Type
Type value in the range 0x2F00 through 0x2FFF. Together, the Type Type value in the range 0x3E00 through 0x3EFF. Together, the Type
and Vendor Id field specify how the Data field is to be inter- and Vendor Id field specify how the Data field is to be
preted. interpreted.
Length Length
Specifies the cumulative length in octets of the Vendor ID and Data Specifies the cumulative length in octets of the Vendor ID and Data
fields. 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 0x2F00 through 0x2FFF 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 (0x2F00-0x2FFF) | Message Length | |U| Msg Type (0x3E00-0x3EFF) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor ID | | Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ + + +
| Remaining Mandatory Parameters | | Remaining Mandatory Parameters |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 74, line 31 skipping to change at page 77, line 49
| Optional Parameters | | Optional Parameters |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit U bit
Unknown message bit. Upon receipt of an unknown message, if U is Unknown message bit. Upon receipt of an unknown message, if U is
clear (=0), a notification is returned to the message originator; clear (=0), a notification is returned to the message originator;
if U is set (=1), the unknown message is silently ignored. if U is set (=1), the unknown message is silently ignored.
The determination as to whether a vendor-private message is under- The determination as to whether a vendor-private message is
stood is based on the Msg Type and the Vendor ID parameter. understood is based on the Msg Type and the Vendor ID parameter.
Msg Type Msg Type
Message type value in the range 0x2F00 through 0x2FFF. 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, Vendor
ID, Remaining Mandatory Parameters and Optional Parameters. 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
skipping to change at page 76, line 17 skipping to change at page 79, line 23
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"
Vendor-Private 0x2F00- "LDP Vendor-private Extensions" Label Abort Request 0x0404 "Label Abort Request Message"
0x2FFF Vendor-Private 0x3E00- "LDP Vendor-private Extensions"
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" FEC 0x0100 "FEC TLV"
Address List 0x0101 "Address List TLV" Address List 0x0101 "Address List TLV"
COS 0x0102 "COS TLV"
Hop Count 0x0103 "Hop Count TLV" Hop Count 0x0103 "Hop Count TLV"
Path Vector 0x0104 "Path Vector TLV" Path Vector 0x0104 "Path Vector TLV"
Generic Label 0x0200 "Generic Label TLV" Generic Label 0x0200 "Generic Label TLV"
ATM Label 0x0201 "ATM Label TLV" ATM Label 0x0201 "ATM Label TLV"
Frame Relay Label 0x0202 "Frame Relay Label TLV" Frame Relay Label 0x0202 "Frame Relay Label TLV"
Status 0x0300 "Status TLV" Status 0x0300 "Status TLV"
Extended Status 0x0301 "Notification Message" Extended Status 0x0301 "Notification Message"
Returned PDU 0x0302 "Notification Message" Returned PDU 0x0302 "Notification Message"
Returned Message 0x0303 "Notification Message" Returned Message 0x0303 "Notification Message"
Common Hello 0x0400 "Hello Message" Common Hello 0x0400 "Hello Message"
Parameters Parameters
Transport Address 0x0401 "Hello Message" Transport Address 0x0401 "Hello Message"
Configuration 0x0402 "Hello Message" Configuration 0x0402 "Hello Message"
Sequence Number Sequence Number
Common Session 0x0500 "Initialization Message" Common Session 0x0500 "Initialization Message"
Parameters Parameters
ATM Session Parameters 0x0501 "Initialization Message" ATM Session Parameters 0x0501 "Initialization Message"
Frame Relay Session 0x0502 "Initialization Message" Frame Relay Session 0x0502 "Initialization Message"
Parameters Parameters
Label Request 0x0600 "Label Request Message" Label Request 0x0600 "Label Mapping Message"
Message Id Message ID
Return Message Id 0x0601 "Label Mapping Message" Vendor-Private 0x3E00- "LDP Vendor-private Extensions"
Vendor-Private 0x2F00- "LDP Vendor-private Extensions" 0x3EFF
0x2FFF
Experimental 0x3F00- "LDP Experimental Extensions" Experimental 0x3F00- "LDP Experimental Extensions"
0x3FFF 0x3FFF
3.9. Status Code Summary 3.9. Status Code Summary
The following are the Status Codes defined in this version of the The following are the Status Codes defined in this version of the
protocol. protocol.
Status Code Type Section Title 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
the Status Code TLV.
Success 0x00000000 "Status TLV" Note that the setting of the Status Code F-bit is at the discretion
Bad LDP Identifer 0x80000001 "Events Signaled by ..." of the LSR originating the Status TLV.
Bad Protocol Version 0x80000002 "Events Signaled by ..."
Bad PDU Length 0x80000003 "Events Signaled by ..." Status Code E Status Data Section Title
Unknown Message Type 0x80000004 "Events Signaled by ..."
Bad Message Length 0x80000005 "Events Signaled by ..." Success 0 0x00000000 "Status TLV"
Unknown TLV 0x80000006 "Events Signaled by ..." Bad LDP Identifer 1 0x00000001 "Events Signaled by ..."
Bad TLV length 0x80000007 "Events Signaled by ..." Bad Protocol Version 1 0x00000002 "Events Signaled by ..."
Malformed TLV Value 0x80000008 "Events Signaled by ..." Bad PDU Length 1 0x00000003 "Events Signaled by ..."
Hold Timer Expired 0x80000009 "Events Signaled by ..." Unknown Message Type 0 0x00000004 "Events Signaled by ..."
Shutdown 0x8000000A "Events Signaled by ..." Bad Message Length 1 0x00000005 "Events Signaled by ..."
Loop Detected 0x0000000B "Loop Detection" Unknown TLV 0 0x00000006 "Events Signaled by ..."
Unknown FEC 0x0000000C "FEC Procedures" Bad TLV length 1 0x00000007 "Events Signaled by ..."
No Route 0x0000000D "Label Request Mess ..." Malformed TLV Value 1 0x00000008 "Events Signaled by ..."
No Label Resources 0x0000000E "Label Request Mess ..." Hold Timer Expired 1 0x00000009 "Events Signaled by ..."
Label Resources Available 0x0000000F "Label Request Mess ..." KeepAlive Timer 1 0x00000009 "Events Signaled by ..."
Session Rejected/ 0x80000010 "Session Initialization" Expired
Shutdown 1 0x0000000A "Events Signaled by ..."
Loop Detected 0 0x0000000B "Loop Detection"
Unknown FEC 0 0x0000000C "FEC Procedures"
No Route 0 0x0000000D "Label Request Mess ..."
No Label Resources 0 0x0000000E "Label Request Mess ..."
Label Resources / 0 0x0000000F "Label Request Mess ..."
Available
Session Rejected/ 1 0x00000010 "Session Initialization"
No Hello No Hello
Session Rejected/ 0x80000011 "Session Initialization" Session Rejected/ 1 0x00000011 "Session Initialization"
Parameters Advertisement Mode Parameters Advertisement Mode
Session Rejected/ 0x80000012 "Session Initialization" Session Rejected/ 1 0x00000012 "Session Initialization"
Parameters Max PDU Length Parameters Max PDU Length
Session Rejected/ 0x80000013 "Session Initialization" Session Rejected/ 1 0x00000013 "Session Initialization"
Parameters Label Range Parameters Label Range
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 [ARCH]) is represented as a Generic
Label TLV with a Label field of 0. Label TLV with a Label field of 0.
4. Security 4. Security Considerations
This section specifies an optional mechanism to protect against the This section specifies an optional mechanism to protect against the
introduction of spoofed TCP segments into LDP session connection introduction of spoofed TCP segments into LDP session connection
streams. streams.
It is based on use of the TCP MD5 Signature Option specified in It is based on use of the TCP MD5 Signature Option specified in
[rfc2385] for use by BGP. See [rfc1321] for a specification of the [rfc2385] for use by BGP. See [rfc1321] for a specification of the
MD5 hash function. MD5 hash function.
4.1. The TCP MD5 Signature Option 4.1. The TCP MD5 Signature Option
skipping to change at page 78, line 45 skipping to change at page 82, line 11
This document describes currrent existing practice for securing This document describes currrent existing practice for securing
BGP against certain simple attacks. It is understood to have BGP against certain simple attacks. It is understood to have
security weaknesses against concerted attacks." security weaknesses against concerted attacks."
"Abstract "Abstract
This memo describes a TCP extension to enhance security for This memo describes a TCP extension to enhance security for
BGP. It defines a new TCP option for carrying an MD5 [RFC1321] BGP. It defines a new TCP option for carrying an MD5 [RFC1321]
digest in a TCP segment. This digest acts like a signature for digest in a TCP segment. This digest acts like a signature for
that segment, incorporating information known only to the con- that segment, incorporating information known only to the
nection end points. Since BGP uses TCP as its transport, using connection end points. Since BGP uses TCP as its transport,
this option in the way described in this paper significantly using this option in the way described in this paper
reduces the danger from certain security attacks on BGP." significantly reduces the danger from certain security attacks
on BGP."
"Introduction "Introduction
The primary motivation for this option is to allow BGP to pro- The primary motivation for this option is to allow BGP to
tect itself against the introduction of spoofed TCP segments protect itself against the introduction of spoofed TCP segments
into the connection stream. Of particular concern are TCP into the connection stream. Of particular concern are TCP
resets. resets.
To spoof a connection using the scheme described in this paper, To spoof a connection using the scheme described in this paper,
an attacker would not only have to guess TCP sequence numbers, an attacker would not only have to guess TCP sequence numbers,
but would also have had to obtain the password included in the but would also have had to obtain the password included in the
MD5 digest. This password never appears in the connection MD5 digest. This password never appears in the connection
stream, and the actual form of the password is up to the appli- stream, and the actual form of the password is up to the
cation. It could even change during the lifetime of a particu- application. It could even change during the lifetime of a
lar connection so long as this change was synchronized on both particular connection so long as this change was synchronized
ends (although retransmission can become problematical in some on both ends (although retransmission can become problematical
TCP implementations with changing passwords). in some TCP implementations with changing passwords).
Finally, there is no negotiation for the use of this option in Finally, there is no negotiation for the use of this option in
a connection, rather it is purely a matter of site policy a connection, rather it is purely a matter of site policy
whether or not its connections use the option." whether or not its connections use the option."
"MD5 as a Hashing Algorithm "MD5 as a Hashing Algorithm
Since this memo was first issued (under a different title), the Since this memo was first issued (under a different title), the
MD5 algorithm has been found to be vulnerable to collision MD5 algorithm has been found to be vulnerable to collision
search attacks [Dobb], and is considered by some to be insuffi- search attacks [Dobb], and is considered by some to be
ciently strong for this type of application. insufficiently strong for this type of application.
This memo still specifies the MD5 algorithm, however, since the This memo still specifies the MD5 algorithm, however, since the
option has already been deployed operationally, and there was option has already been deployed operationally, and there was
no "algorithm type" field defined to allow an upgrade using the no "algorithm type" field defined to allow an upgrade using the
same option number. The original document did not specify a same option number. The original document did not specify a
type field since this would require at least one more byte, and type field since this would require at least one more byte, and
it was felt at the time that taking 19 bytes for the complete it was felt at the time that taking 19 bytes for the complete
option (which would probably be padded to 20 bytes in TCP option (which would probably be padded to 20 bytes in TCP
implementations) would be too much of a waste of the already implementations) would be too much of a waste of the already
limited option space. limited option space.
skipping to change at page 80, line 9 skipping to change at page 83, line 21
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].
4.2. LDP Use of the TCP MD5 Signature Option 4.2. LDP Use of the TCP MD5 Signature Option
LDP uses the TCP MD5 Signature Option as follows: LDP uses the TCP MD5 Signature Option as follows:
- Use of the MD5 Signature Option for LDP TCP connections is a con- - Use of the MD5 Signature Option for LDP TCP connections is a
figurable LSR option. configurable LSR option.
- An LSR that uses the MD5 Signature Option is configured with a - An LSR that uses the MD5 Signature Option is configured with a
password for each potential LDP peer. password for each potential LDP peer.
- The LSR applies the MD5 algorithm as specified in [RFC2385] to - The LSR applies the MD5 algorithm as specified in [RFC2385] to
compute the MD5 digest for a TCP segment to be sent to a peer. compute the MD5 digest for a TCP segment to be sent to a peer.
This computation makes use of the peer password as well as the This computation makes use of the peer password as well as the
TCP segment. TCP segment.
- When the LSR receives a TCP segment with an MD5 digest, it vali- - When the LSR receives a TCP segment with an MD5 digest, it
dates the segment by calculating the MD5 digest (using its own validates the segment by calculating the MD5 digest (using its
record of the password) and compares the computed digest with the own record of the password) and compares the computed digest with
received digest. If the comparison fails, the segment is dropped the received digest. If the comparison fails, the segment is
without any response to the sender. 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 has
not been configured. This ensures that the LSR establishes LDP not been configured. This ensures that the LSR establishes LDP
TCP connections only with LSRs for which a password has been con- TCP connections only with LSRs for which a password has been
figured. configured.
5. Intellectual Property Considerations 5. 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 docu- regard to some or all of the specification contained in this
ment. For more information consult the online list of claimed document. For more information consult the online list of claimed
rights. rights.
6. Acknowledgments 6. 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.
7. References 7. References
[ARCH] E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label [ARCH] E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label
Switching Architecture", Work in Progress, July 1998. Switching Architecture", Work in Progress, July 1998.
[ATM] B. Davie, J. Lawrence, K. McCloghrie, Y. Rekhter, E. Rosen, G. [ATM] B. Davie, J. Lawrence, K. McCloghrie, Y. Rekhter, E. Rosen, G.
Swallow, P. Doolan, "Use of Label Switching With ATM", Work in Pro- Swallow, P. Doolan, "Use of Label Switching With ATM", Work in
gress, September, 1998. Progress, September, 1998.
[ATM-VP] N. Feldman, B. Jamoussi, S. Komandur, A, Viswanathan, T
Worster, "MPLS using ATM VP Switching", Work in Progress, February,
1999.
[CRLDP] L. Andersson, A. Fredette, B. Jamoussi, R. Callon, P. Doolan, [CRLDP] L. Andersson, A. Fredette, B. Jamoussi, R. Callon, P. Doolan,
N. Feldman, E. Gray, J. Halpern, J. Heinanen T. E. Kilty, A. G. N. Feldman, E. Gray, J. Halpern, J. Heinanen T. E. Kilty, A. G.
Malis, M. Girish, K. Sundell, P. Vaananen, T. Worster, L. Wu, R. Malis, M. Girish, K. Sundell, P. Vaananen, T. Worster, L. Wu, R.
Dantu, "Constraint-Based LSP Setup using LDP", Work in Progress, Dantu, "Constraint-Based LSP Setup using LDP", Work in Progress,
January, 1999. January, 1999.
[DIFFSERV] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. [DIFFSERV] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W.
Weiss, "An Architecture for Differentiated Services", Work in Pro- Weiss, "An Architecture for Differentiated Services", Work in
gress, October, 1998. Progress, October, 1998.
[ENCAP] E. Rosen, Y. Rekhter, D. Tappan, D. Farinacci, G. Fedorkow, [ENCAP] E. Rosen, Y. Rekhter, D. Tappan, D. Farinacci, G. Fedorkow,
T. Li, A. Conta, "MPLS Label Stack Encoding", Work in Progress, July, T. Li, A. Conta, "MPLS Label Stack Encoding", Work in Progress, July,
1998. 1998.
[FR] A. Conta, P. Doolan, A. Malis, "Use of Label Switching on Frame [FR] A. Conta, P. Doolan, A. Malis, "Use of Label Switching on Frame
Relay Networks", Work in Progress, October, 1998. Relay Networks", Work in Progress, October, 1998.
[FRAMEWORK] R. Callon, P. Doolan, N. Feldman, A. Fredette, G. Swal- [FRAMEWORK] R. Callon, P. Doolan, N. Feldman, A. Fredette, G.
low, A. Viswanathan, "A Framework for Multiprotocol Label Switching", Swallow, A. Viswanathan, "A Framework for Multiprotocol Label
Work in Progress, November 1997. Switching", Work in Progress, November 1997.
[LSPTUN] D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow, Vijay [LSPTUN] D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow, Vijay
Srinivasan, "Extensions to RSVP for LSP Tunnels", Work in Progress, Srinivasan, "Extensions to RSVP for LSP Tunnels", Work in Progress,
November 1998. November 1998.
[rfc1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC 1321, [rfc1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC 1321,
April 1992. April 1992.
[rfc1483] J. Heinanen, "Multiprotocol Encapsulation over ATM Adapta- [rfc1483] J. Heinanen, "Multiprotocol Encapsulation over ATM
tion Layer 5", RFC 1483, Telecom Finland, July 1993. Adaptation Layer 5", RFC 1483, Telecom Finland, July 1993.
[rfc1583] J. Moy, "OSPF Version 2", RFC 1583, Proteon Inc, March [rfc1583] J. Moy, "OSPF Version 2", RFC 1583, Proteon Inc, March
1994. 1994.
[rfc1700] J. Reynolds, J.Postel, "ASSIGNED NUMBERS", October 1994. [rfc1700] J. Reynolds, J.Postel, "ASSIGNED NUMBERS", October 1994.
[rfc1771] Y. Rekhter, T. Li, "A Border Gateway Protocol 4 (BGP-4)", [rfc1771] Y. Rekhter, T. Li, "A Border Gateway Protocol 4 (BGP-4)",
RFC 1771, IBM Corp, Cisco Systems, March 1995. RFC 1771, IBM Corp, Cisco Systems, March 1995.
[rfc2205] R. Braden, L. Zhang, S. Berson, S. Herzog, S. Jamin, [rfc2205] R. Braden, L. Zhang, S. Berson, S. Herzog, S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specif- "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
ication", RFC 2205, September 1997. Specification", RFC 2205, September 1997.
[rfc2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 [rfc2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, August 1998. Signature Option", RFC 2385, August 1998.
[TE] D. Awduche, J. Malcolm, J Agogbua, M. O'Dell, J. McManus, " [TE] D. Awduche, J. Malcolm, J Agogbua, M. O'Dell, J. McManus, "
Requirements for Traffic Engineering over MPLS", Work in Progress, Requirements for Traffic Engineering over MPLS", Work in Progress,
October 1998. October 1998.
8. Author Information 8. Author Information
skipping to change at page 83, line 12 skipping to change at page 87, line 12
Phone: 914-784-3254 Phone: 914-784-3254
email: nkf@us.ibm.com email: nkf@us.ibm.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 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 / 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:
skipping to change at page 83, line 46 skipping to change at page 87, line 48
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 [ARCH] 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 downstream
LSR to determine when to distribute a label for a FEC to LDP LSR to determine when to distribute a label for a FEC to LDP
peers. The architecture defines four Label Distribution pro- peers. The architecture defines four Label Distribution
cedures: procedures:
. Downstream Unsolicited Independent Control, called PushUncon- . Downstream Unsolicited Independent Control, called
ditional in [ARCH]. PushUnconditional in [ARCH].
. Downstream Unsolicited Ordered Control, called PushCondi- . Downstream Unsolicited Ordered Control, called
tional in [ARCH]. PushConditional in [ARCH].
. Downstream On Demand Independent Control, called PulledUncon- . Downstream On Demand Independent Control, called
ditional in [ARCH]. PulledUnconditional in [ARCH].
. Downstream On Demand Ordered Control, called PulledCondi- . Downstream On Demand Ordered Control, called
tional in [ARCH]. PulledConditional in [ARCH].
- 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 previously
distributed to LDP peers. The architecture defines a single Label distributed to LDP peers. The architecture defines a single Label
Withdrawal procedure. Whenever an LSR breaks the binding between Withdrawal procedure. Whenever an LSR breaks the binding between
a label and a FEC, it must withdraw the FEC label mapping from a label and a FEC, it must withdraw the FEC label mapping from
all LDP peers to which it has previously sent the mapping. 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 to
determine when to explicitly request that a downstrem LSR bind a determine when to explicitly request that a downstrem LSR bind a
label to a FEC and send it the corresponding label mapping. The label to a FEC and send it the corresponding label mapping. The
architecture defines three Label Request procedures: 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 it
needs one. needs one.
. Request On Request. This procedure is used by non-label merg- . Request On Request. This procedure is used by non-label
ing LSRs. The LSR requests a label when it receives a request merging LSRs. The LSR requests a label when it receives a
for one, in addition to whenever it needs one. 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 to
determine when to release a previously received label mapping for determine when to release a previously received label mapping for
a FEC. The architecture defines two Label Release procedures: 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]. [ARCH].
. Liberal label retention, called No Release On Change in . Liberal label retention, called No Release On Change in
[ARCH]. [ARCH].
- 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 from
a FEC next hop for forwarding/switching. 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 deter- FEC next hop for forwarding/switching only if it has
mined that by doing so it will not cause a forwarding loop. determined that by doing so it will not cause a forwarding
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 mechanism;
therefore, the procedures below do not make use of the Use If therefore, the procedures below do not make use of the Use If
Loop Free procedure. Loop Free procedure.
skipping to change at page 85, line 34 skipping to change at page 89, line 38
. 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
an algorithm for each label distribution event. The requirement on
an LDP implementation is that its event handling must have the effect
specifid by the algorithms. That is, an implementation need not
follow exactly the steps specified by the algorithms as long as the
effect is identical.
The algorithms for handling label distribution events share common The algorithms for handling label distribution events share common
actions. The specifications below package these common actions into actions. The specifications below package these common actions into
procedure units. Specifications for these common procedures are in procedure units. Specifications for these common procedures are in
their own section "Common Label Distribution Procedures", which fol- their own section "Common Label Distribution Procedures", which
lows 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:
skipping to change at page 86, line 29 skipping to change at page 90, line 33
- Installation of labels for forwarding/switching use by the LSR. - Installation of labels for 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.
- RAttributes. Attributes received with the message. E.g., CoS, Hop - RAttributes. Attributes received with the message. E.g., Hop
Count Path Vector. Count Path Vector.
- SAttributes. Attributes to be included in Label Request message, - SAttributes. Attributes to be included in Label Request message,
if any, propagated to FEC Next Hop. if any, propagated to FEC Next Hop.
- StoredHopCount. The hop count, if any, previously recorded for - StoredHopCount. The hop count, if any, previously recorded for
the FEC. the FEC.
Algorithm: Algorithm:
LRq.1 Execute procedure Check_Received_Attributes (MsgSource, RAt- LRq.1 Execute procedure Check_Received_Attributes (MsgSource,
tributes). RAttributes).
If Loop Detected, goto LRq.11. If Loop Detected, goto LRq.13.
LRq.2 Is there a Next Hop for FEC? LRq.2 Is there a Next Hop for FEC?
If so, goto LRq.4. If so, goto LRq.5.
LRq.3 Execute procedure Send_Notification (MsgSource, No Route). LRq.3 Is MsgSource the Next Hop?
Goto LRq.11. Ifnot, goto LRq.5.
LRq.4 Has LSR previously received a label request for FEC from LRq.4 Execute procedure Send_Notification (MsgSource, Loop
Detected).
Goto LRq.13
LRq.5 Execute procedure Send_Notification (MsgSource, No Route).
Goto LRq.13.
LRq.6 Has LSR previously received a label request for FEC from
MsgSource? MsgSource?
If not, goto LRq.6. (See Note 1.) If not, goto LRq.8. (See Note 1.)
LRq.5 Is the label request a duplicate request?
If so, Goto LRq.11. (See Note 2.)
LRq.6 Record label request for FEC received from MsgSource and mark LRq.7 Is the label request a duplicate request?
If so, Goto LRq.13. (See Note 2.)
LRq.8 Record label request for FEC received from MsgSource and mark
it pending. it pending.
LRq.7 Perform LSR Label Distribution procedure: LRq.9 Perform LSR Label Distribution procedure:
For Downstream Unsolicited Independent Control OR For Downstream Unsolicited Independent Control OR
For Downstream On Demand Independent Control For Downstream On Demand Independent Control
1. Has LSR previously received and retained a label map- 1. Has LSR previously received and retained a label
ping for FEC from Next Hop?. mapping for FEC from Next Hop?.
Is so, set Propagating to IsPropagating. Is so, set Propagating to IsPropagating.
If not, set Propagating to NotPropagating. If not, set Propagating to NotPropagating.
2. Execute procedure 2. Execute procedure
Prepare_Label_Mapping_Attributes(MsgSource, FEC, RAt- Prepare_Label_Mapping_Attributes(MsgSource, FEC,
tributes, SAttributes, Propagating, StoredHopCount). RAttributes, SAttributes, Propagating,
StoredHopCount).
3. Execute procedure Send_Label (MsgSource, FEC, SAttri- 3. Execute procedure Send_Label (MsgSource, FEC,
butes). SAttributes).
4. Is LSR egress for FEC? OR 4. Is LSR egress for FEC? OR
Has LSR previously received and retained a label map- Has LSR previously received and retained a label
ping for FEC from Next Hop? mapping for FEC from Next Hop?
If so, goto LRq.9. If not, goto LRq.8. If so, goto LRq.11. If not, goto LRq.10.
For Downstream Unsolicited Ordered Control OR For Downstream Unsolicited Ordered Control OR
For Downstream On Demand Ordered Control For Downstream On Demand Ordered Control
1. Is LSR egress for FEC? OR 1. Is LSR egress for FEC? OR
Has LSR previously received and retained a label map- Has LSR previously received and retained a label
ping for FEC from Next Hop? mapping for FEC from Next Hop?
If not, goto LRq.8. If not, goto LRq.10.
2. Execute procedure 2. Execute procedure
Prepare_Label_Mapping_Attributes(MsgSource, FEC, RAt- Prepare_Label_Mapping_Attributes(MsgSource, FEC,
tributes, SAttributes, IsPropagating, StoredHopCount) RAttributes, SAttributes, IsPropagating,
StoredHopCount)
3. Execute procedure Send_Label (MsgSource, FEC, SAttri- 3. Execute procedure Send_Label (MsgSource, FEC,
butes). SAttributes).
Goto LRq.9. Goto LRq.11.
LRq.8 Perform LSR Label Request procedure: LRq.10 Perform LSR Label Request procedure:
For Request Never For Request Never
1. Goto LRq.11.
1. Goto LRq.13.
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 Prepare_Label_Request_Attributes
(Next Hop, FEC, RAttributes, SAttributes); (Next Hop, FEC, RAttributes, SAttributes);
2. Execute procedure Send_Label_Request (Next Hop, FEC, 2. Execute procedure Send_Label_Request (Next Hop, FEC,
SAttributes). SAttributes).
Goto LRq.11. Goto LRq.13.
LRq.9 Has LSR successfully sent a label for FEC to MsgSource? LRq.11 Has LSR successfully sent a label for FEC to MsgSource?
If not, goto LRq.11. (See Note 3.) If not, goto LRq.13. (See Note 3.)
LRq.10 Perform LSR Label Use procedure. LRq.12 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. Install label sent to MsgSource and label from Next 1. Install label sent to MsgSource and label from Next
Hop (if LSR is not egress) for forwarding/switching Hop (if LSR is not egress) for forwarding/switching
use. use.
LRq.11 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 dis- requested a label for FEC from it. The LSR must be able to
tinguish such requests from a non-label merging MsgSource from distinguish such requests from a non-label merging MsgSource
duplicate label requests. from duplicate label requests.
The LSR uses the message ID of received Label Request messages
to detect duplicate requests. This means that an LSR (the
upstream peer) may not reuse the message ID used for a Label
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
skipping to change at page 89, line 40 skipping to change at page 94, line 14
- 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 to
an upstream peer. 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., CoS, 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, pro- - SAttributes to be included in Label Mapping message, if any,
pagated 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 label
request for FEC previously sent to MsgSource. request for FEC previously sent to MsgSource.
If not, goto LMp.9. If not, goto LMp.9.
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, RAt- LMp.3 Execute procedure Check_Received_Attributes (MsgSource,
tributes). 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 FEC
from MsgSource? from MsgSource?
If not, goto LMp.8. (See Note 1.). If not, goto LMp.8. (See Note 1.).
LMp.5 Does the label previously received from MsgSource match Label LMp.5 Does the label previously received from MsgSource match Label
(i.e., the label received in the message)? (i.e., the label received in the message)?
If not, goto LMp.8. (See Note 2.) If not, goto LMp.8. (See Note 2.)
LMp.6 Delete matching label mapping for FEC previously received LMp.6 Delete matching label mapping for FEC previously received
from MsgSource. from MsgSource.
LMp.7 Remove Label from forwarding/switching use. (See Note 3.). LMp.7 Remove Label from forwarding/switching use. (See Note 3.).
Goto LMp.26.
LMp.8 Execute procedure Send_Message (MsgSource, Label Release, LMp.8 Execute procedure Send_Message (MsgSource, Label Release,
FEC, Label). Goto LMp.26. FEC, Label). Goto LMp.26.
LMp.9 Determine the Next Hop for FEC. LMp.9 Determine the Next Hop for FEC.
LMp.10 Is MsgSource the Next Hop for FEC? LMp.10 Is MsgSource the Next Hop for FEC?
If so, goto LMp.12. If so, goto LMp.12.
LMp.11 Perform LSR Label Release procedure: LMp.11 Perform LSR Label Release procedure:
For Conservative Label retention: For Conservative Label retention:
1. Execute procedure Send_Message (MsgSource, Label 1. Execute procedure Send_Message (MsgSource, Label
Release, FEC, Label). Release, FEC, Label).
Goto LMp.26. Goto LMp.26.
For Liberal Label retention: For Liberal Label retention:
1. Record label mapping for FEC with Label and RAttri- 1. Record label mapping for FEC with Label and
butes has been received from MsgSource. RAttributes has been received from MsgSource.
Goto LMp.26. Goto LMp.26.
LMp.12 Does LSR have a previously received label mapping for FEC LMp.12 Does LSR have a previously received label mapping for FEC
from MsgSource? from MsgSource?
If not, goto LMp.14 If not, goto LMp.14
LMp.13 Does the label previously received from MsgSource match Label LMp.13 Does the label previously received from MsgSource match Label
(i.e., the label received in the message)? (i.e., the label received in the message)?
If not, goto LMp.8. (See Note 2.) If not, goto LMp.8. (See Note 2.)
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 has
been received from MsgSource. been received from MsgSource.
LMp.17 Iterate through for LMp.25 for each Peer, other than LMp.17 Iterate through for LMp.25 for each Peer, other than
MsgSource. MsgSource.
skipping to change at page 91, line 30 skipping to change at page 96, line 4
If so, goto LMp.24. (See Note 4.) If so, goto LMp.24. (See Note 4.)
LMp.20 Execute procedure Prepare_Label_Mapping_Attributes(Peer, FEC, LMp.20 Execute procedure Prepare_Label_Mapping_Attributes(Peer, FEC,
RAttributes, SAttributes, IsPropagating, StoredHopCount). 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). (See Note 5.) PrevAdvLabel, SAttributes). (See Note 5.)
LMp.22 Update record of label mapping for FEC previously sent to LMp.22 Update record of label mapping for FEC previously sent to
Peer to include the new attributes sent. Peer to include the new attributes sent.
Goto LMp.24. Goto LMp.24.
LMp.23 Perform LSR Label Distribution procedure: LMp.23 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, RAttri- Prepare_Label_Mapping_Attributes(Peer, FEC,
butes, SAttributes, IsPropagating, UnknownHopCount). RAttributes, SAttributes, IsPropagating,
UnknownHopCount).
2. Execute procedure Send_Label (Peer, FEC, SAttri- 2. Execute procedure Send_Label (Peer, FEC,
butes). 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.
3. Goto LMp.24. 3. Goto LMp.24.
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. Does LSR have a label request for FEC from Peer 1. Does LSR have a label request for FEC from Peer
marked as pending? marked as pending?
If not, continue iteration for next Peer at LMp.17. If not, continue iteration for next Peer at LMp.17.
2. Execute procedure 2. Execute procedure
Prepare_Label_Mapping_Attributes(Peer, FEC, RAttri- Prepare_Label_Mapping_Attributes(Peer, FEC,
butes, SAttributes, IsPropagating, UnknownHopCount) RAttributes, SAttributes, IsPropagating,
UnknownHopCount)
3. Execute procedure Send_Label (Peer, FEC, SAttri- 3. Execute procedure Send_Label (Peer, FEC,
butes). 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. Goto LMp.24. 4. Goto LMp.24.
LMp.24 Perform LSR Label Use procedure: LMp.24 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
skipping to change at page 92, line 47 skipping to change at page 97, line 23
2. A mapping with a different label from the same peer would be an 2. A mapping with a different label from the same peer would be an
attempt to establish multipath label switching, which is not attempt to establish multipath label switching, which is not
supported in this version of LDP. supported in this version of LDP.
3. If Label is not in forwarding/switching use, LMp.7 has no 3. If Label is not in forwarding/switching use, LMp.7 has no
effect. effect.
4. The loop detection Path Vector attribute is considered in this 4. 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 pre- received Path Vector is inconsistent with the Path Vector
viously sent to the Peer, then the attributes are considered to previously sent to the Peer, then the attributes are considered
be inconsistent. Note that an LSR is not required to store a to be inconsistent. Note that an LSR is not required to store
received Path Vector after it propagates the Path Vector in a a received Path Vector after it propagates the Path Vector in a
mapping message. If an LSR does not store the Path Vector, it mapping message. If an LSR does not store the Path Vector, it
has no way to check the consistency of a newly received Path has no way to check the consistency of a newly received Path
Vector. This means that whenever such an LSR receives a map- Vector. This means that whenever such an LSR receives a
ping message carrying a Path Vector it must always propagate mapping message carrying a Path Vector it must always propagate
the Path Vector. the Path Vector.
5. LMp.19 through LMp.21 deal with a situation that can arise when 5. LMp.19 through LMp.21 deal with a situation that can arise when
the LSR is using independent control and it receives a mapping the LSR is using independent control and it receives a mapping
from the downstream peer after it has sent a mapping to an from the downstream peer after it has sent a mapping to an
upstream peer. In this situation the LSR needs to propagate any upstream peer. In this situation the LSR needs to propagate any
changed attributes, such as Hop Count, upstream. If Loop Detec- changed attributes, such as Hop Count, upstream. If Loop
tion is configured on, the propagated attributes must include Detection is configured on, the propagated attributes must
the Path Vector include the Path Vector
A.1.3. Receive Label Release A.1.3. Receive Label Abort Request
Summary:
When an LSR receives a label abort request message from a peer, it
checks whether it has already responded to the label request in
question. If it has, it silently ignores the message. If it has
not, it sends the peer a Label Request Aborted Notification. 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
the downstream peer to abort the LSP.
Context:
- LSR. The LSR handling the event.
- MsgSource. The LDP peer that sent the message.
- FEC. The FEC specified in the message.
- RequestMessageID. The message ID of the label request message to
be aborted.
- Next Hop. The next hop for the FEC.
Algorithm:
LAbR.1 Does the message match a previously received label request
message from MsgSource? (See Note 1.)
If not, goto LAbR.12.
LAbR.2 Has LSR responded to the previously received label request?
If so, goto LAbR.12.
LAbR.3 Execute procedure Send_Message(MsgSource, Notification, Label
Request Aborted, TLV), where TLV is the Label Request Message
ID TLV received in the label abort request message.
LAbR.4 Does LSR have a label request message outstanding for FEC?
If so, goto LAbR.7
LAbR.5 Does LSR have a label mapping for FEC?
If not, goto LAbR.11
LAbR.6 Generate Event: Received Label Release Message for FEC from
MsgSource. (See Note 2.)
Goto LAbR.11.
LAbR.7 Is LSR merging the LSP for FEC?
If not, goto LAbR.9.
LAbR.8 Are there upstream peers other than MsgSource that have
requested a label for FEC?
If so, goto LAbR.11.
LAbR.9 Execute procedure Send_Message (Next Hop, Label Abort
Request, FEC, TLV), where TLV is the Label Request Message ID
TLV received in the label abort request message from
MsgSource.
LAbR.10 Record that a label abort request for FEC is pending.
LAbR.11 Delete record of label request for FEC from MsgSource.
LAbR.12 DONE
Notes:
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
previously received label request from MsgSource.
2. If LSR has received a label mapping from NextHop, it should
behave as if it had advertised a label mapping to MsgSource and
MsgSource has released it.
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 peer,
it checks whether other peers hold the released label. If none do, it checks whether other peers hold the released label. If none do,
the LSR removes the label from forwarding/switching use, if it has the LSR removes the label from forwarding/switching use, if it has
not already done so, and if the LSR holds a label mapping from the not already done so, and if the LSR holds a label mapping from the
FEC next hop, it releases the label mapping. FEC next hop, it releases the label mapping.
Context: Context:
skipping to change at page 93, line 42 skipping to change at page 99, line 46
- 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 pre- LRl.2 Does message match an outstanding label withdraw for FEC
viously 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 previ- LRl.3 Delete record of outstanding label withdraw for FEC
ously 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 other
peers? 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?
skipping to change at page 95, line 6 skipping to change at page 101, line 9
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 impor- are a scarce resource in the operating environment; the
tance of keeping LSP setup latency low by keeping the amount of importance of keeping LSP setup latency low by keeping the
signalling required small; whether LSP setup is ingress- amount of signalling required small; whether LSP setup is
controlled or egress-controlled in the operating environment. ingress-controlled or egress-controlled in the operating
environment.
A.1.4. 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 LDP
peer, it responds with a label release message and it removes the peer, it responds with a label release message and it removes the
label from any forwarding/switching use. If ordered control is in label from any forwarding/switching use. If ordered control is in
use, the LSR sends a label withdraw message to each LDP peer to use, the LSR sends a label withdraw message to each LDP peer to
which it had previously sent a label mapping for the FEC. If the which it had previously sent a label mapping for the FEC. If the
LSR is using Downstream on Demand label advertisement with indepen- LSR is using Downstream on Demand label advertisement with
dent control, it then acts as if it had just recognized the FEC. independent control, it then acts as if it had just recognized the
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.
skipping to change at page 96, line 19 skipping to change at page 102, line 24
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 interation for next Peer at LWd.8. If not, continue interation 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 withdrawn
Label? Label?
If not, continue iteration for next Peer at LWd.8. (See Note If not, continue iteration for next Peer at LWd.8. (See Note
3.) 3.)
LWd.11 Execute procedure Send_Label_Withdraw (Peer, FEC, Label pre- LWd.11 Execute procedure Send_Label_Withdraw (Peer, FEC, Label
viously 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.1.5. Recognize New FEC A.1.6. Recognize New FEC
Summary: Summary:
The response by an LSR to learning a new FEC may involve one or The response by an LSR to learning a new FEC via the routing table
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.
skipping to change at page 97, line 34 skipping to change at page 103, line 42
any, previously received from Next Hop. 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 map- 2. Has LSR previously received and retained a label
ping 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 map- Has LSR previously received and retained a label
ping 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. xecute procedure Prepare_Label_Mapping_Attributes 3. xecute 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.
skipping to change at page 99, line 8 skipping to change at page 105, line 13
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. (See
Note 3.) 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 CoS. The means by which FEC InitAttributes, if any, are is one which specifies desired LSP characteristics, such as
specified is beyond the scope of LDP. Note that the InitAttri- class of service (CoS). (Note that while the current version
butes will not include a known Hop Count or a Path Vector. of LDP does not specify a CoS attribute, LDP extensions may.)
The means by which FEC InitAttributes, if any, are specified is
beyond the scope of LDP. Note that the InitAttributes will not
include a known Hop Count or a Path Vector.
2. An LSR using Downstream On Demand label distribution would send 2. An LSR using Downstream On Demand label distribution would send
a label only if it had a previously received label request a label only if it had a previously received label request
marked as pending. The LSR would have no such pending requests marked as pending. The LSR would have no such pending requests
because it responds to any label request for an unknown FEC by because it responds to any label request for an unknown FEC by
sending the requesting LSR a No Route notification and discard- sending the requesting LSR a No Route notification and
ing the label request; see LRq.3 discarding the label request; see LRq.3
3. If the LSR has a label for the FEC from the Next Hop, it should 3. If the LSR has a label for the FEC from the Next Hop, it should
behave as if it had just received the label from the Next Hop. behave as if it had just received the label from the Next Hop.
This occurs in the case of Liberal label retention mode. This occurs in the case of Liberal label retention mode.
A.1.6. Detect change in FEC next hop A.1.7. Detect Change in FEC Next Hop
Summary: Summary:
The response by an LSR to a change in the next hop for a FEC may The response by an LSR to a change in the next hop for a FEC may
involve one or more of the following actions: involve one or more of the following actions:
- Removal of the label from the FEC's old next hop from - Removal of the label from the FEC's old next hop from
forwarding/switching use; forwarding/switching use;
- Transmission of label mappping messages for the FEC to one or - Transmission of label mappping messages for the FEC to one or
skipping to change at page 100, line 27 skipping to change at page 106, line 35
NH.1 Has LSR previously received and retained a label mapping for NH.1 Has LSR previously received and retained a label mapping for
FEC from Old Next Hop? FEC from Old Next Hop?
If not, goto NH.6. If not, goto NH.6.
NH.2 Remove label from forwarding/switching use. (See Note 1.) NH.2 Remove label from forwarding/switching use. (See Note 1.)
NH.3 Is LSR using Liberal label retention? NH.3 Is LSR using Liberal label retention?
If so, goto NH.6. If so, goto NH.6.
NH.4 Execute procedure Send_Message (Old Next Hop, Label Release, NH.4 Execute procedure Send_Message (Old Next Hop, Label Release,
OldLlabel). OldLabel).
NH.5 Delete label mapping for FEC previously received from Old NH.5 Delete label mapping for FEC previously received from Old
Next Hop. Next Hop.
NH.6 Is there a New Next Hop for the FEC? NH.6 Does LSR have a label request pending with Old Next Hop?
If not, goto NH.12. If not, goto NH.10.
NH.7 Has LSR previously received and retained a label mapping for NH.7 Is LSR using Conservative label retention?
If not, goto NH.10.
NH.8 Execute procedure Send_Message (Old Next Hop, Label Abort
Request, FEC, TLV), where TLV is a Label Request Message ID
TLV that carries the message ID of the pending label request.
NH.9 Record a label abort request is pending for FEC with Old Next
Hop.
NH.10 Is there a New Next Hop for the FEC?
If not, goto NH.16.
NH.11 Has LSR previously received and retained a label mapping for
FEC from New Next Hop? FEC from New Next Hop?
If not, goto NH.9. If not, goto NH.13.
NH.8 Generate Event: Received Label Mapping from New Next Hop. NH.12 Generate Event: Received Label Mapping from New Next Hop.
Goto NH.12. (See Note 2.) Goto NH.20. (See Note 2.)
NH.9 Is LSR using Downstream on Demand advertisement? OR NH.13 Is LSR using Downstream on Demand advertisement? OR
Is Next Hop using Downstream on Demand advertisement? OR Is Next Hop using Downstream on Demand advertisement? OR
Is LSR using Conservative label retention? (See Note 3.) Is LSR using Conservative label retention? (See Note 3.)
If so, goto NH.10. If not, goto NH.12. If so, goto NH.14.
If not, goto NH.20.
NH.10 Execute procedure Prepare_Label_Request_Attributes (Next NH.14 Execute procedure Prepare_Label_Request_Attributes (Next Hop,
Hop, FEC, CurAttributes, SAttributes) FEC, CurAttributes, SAttributes)
NH.11 Execute procedure Send_Label_Request (New Next Hop, FEC, SAt- NH.15 Execute procedure Send_Label_Request (New Next Hop, FEC,
tributes). SAttributes). (See Note 4.)
(See Note 4.) Goto NH.20.
NH.11 DONE.
NH.16 Iterate through NH.19 for each Peer.
NH.17 Has LSR previously sent a label maping for FEC to Peer?
If not, continue iteration for next Peer at NH.16.
NH.18 Execute procedure Send_Label_Withdraw (Peer, FEC, Label
previously sent to Peer).
NH.19 End iteration from NH.16.
NH.20 DONE.
Notes: Notes:
1. If Label is not in forwarding/switching use, NH.2 has no 1. If Label is not in forwarding/switching use, NH.2 has no
effect. effect.
2. If the LSR has a label for the FEC from the New Next Hop, it 2. If the LSR has a label for the FEC from the New Next Hop, it
should behave as if it had just received the label from the New should behave as if it had just received the label from the New
Next Hop. Next Hop.
skipping to change at page 101, line 27 skipping to change at page 108, line 12
Label Mapping message where the LSR operating in Conservative Label Mapping message where the LSR operating in Conservative
Label retention mode may have released a label mapping received Label retention mode may have released a label mapping received
from the New Next Hop before it detected the FEC next hop had from the New Next Hop before it detected the FEC next hop had
changed. changed.
4. Regardless of the Label Request procedure in use by the LSR, it 4. Regardless of the Label Request procedure in use by the LSR, it
must send a label request if the conditions in NH.8 hold. must send a label request if the conditions in NH.8 hold.
Therefore it executes the Send_Label_Request procedure directly Therefore it executes the Send_Label_Request procedure directly
rather than perform LSR Label Request procedure. rather than perform LSR Label Request procedure.
A.1.7. Receive Notification / No Label Resources A.1.8. Receive Notification / Label Request Aborted
Summary:
When an LSR receives a Label Request Aborted notification from an
LDP peer it records that the corresponding label request
transaction, if any, has completed.
Context:
- LSR. The LSR handling the event.
- FEC. The FEC for which a label was requested.
- RequestMessageID. The message ID of the label request message to
be aborted.
- MsgSource. The LDP peer that sent the Notification message.
Algorithm:
LRqA.1 Does the notification correspond to an outstanding label
request abort for FEC? (See Note 1).
If not, goto LRqA.3.
LRqA.2 Record that the label request for FEC has been aborted.
LRqA.3 DONE
Notes:
1. The LSR uses the FEC and RequestMessageID to locate its record,
if any, of the outstanding label request abort.
A.1.9. Receive Notification / No Label Resources
Summary: Summary:
When an LSR receives a No Label Resources notification from an LDP When an LSR receives a No Label Resources notification from an LDP
peer, it stops sending label request messages to the peer until it peer, it stops sending label request messages to the peer until it
receives a Label Resources Available Notification from the peer. receives a Label Resources Available Notification from the peer.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
skipping to change at page 102, line 10 skipping to change at page 109, line 34
MsgSource. MsgSource.
NoRes.2 Record label mapping for FEC from MsgSource is needed but NoRes.2 Record label mapping for FEC from MsgSource is needed but
that no label resources are available. that no label resources are available.
NoRes.3 Set status record indicating it is not OK to send label NoRes.3 Set status record indicating it is not OK to send label
requests to MsgSource. requests to MsgSource.
NoRes.4 DONE. NoRes.4 DONE.
A.1.8. Receive Notification / No Route A.1.10. Receive Notification / No Route
Summary: Summary:
When an LSR receives a No Route notification from an LDP peer in When an LSR receives a No Route notification from an LDP peer in
response to a Label Request message, the Label No Route procedure response to a Label Request message, the Label No Route procedure
in use dictates its response. The LSR either will take no further in use dictates its response. The LSR either will take no further
action, or it will defer the label request by starting a timer and action, or it will defer the label request by starting a timer and
send another Label Request message to the peer when the timer later send another Label Request message to the peer when the timer later
expires. expires.
skipping to change at page 103, line 5 skipping to change at page 110, line 31
For Request Retry For Request Retry
1. Record deferred label request for FEC and Attributes 1. Record deferred label request for FEC and Attributes
to be sent to MsgSource. to be sent to MsgSource.
2. Start timeout. Goto NoNH.3. 2. Start timeout. Goto NoNH.3.
NoNH.3 DONE. NoNH.3 DONE.
A.1.9. Receive Notification / Loop Detected A.1.11. Receive Notification / Loop Detected
Summary: Summary:
When an LSR receives a Loop Detected notification from an LDP peer When an LSR receives a Loop Detected notification from an LDP peer
in response to a Label Request message, it behaves as if it had in response to a Label Request message, it behaves as if it had
received a No Route notification. received a No Route notification.
Context: Context:
See "Receive Notification / No Route". See "Receive Notification / No Route".
Algorithm: Algorithm:
See "Receive Notification / No Route" See "Receive Notification / No Route"
A.1.10. Receive Notification / Label Resources Available A.1.12. Receive Notification / Label Resources Available
Summary: Summary:
When an LSR receives a Label Resources Available notification from When an LSR receives a Label Resources Available notification from
an LDP peer, it resumes sending label requests to the peer. an LDP peer, it resumes sending label requests to the peer.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- MsgSource. The LDP peer that sent the Notification message. - MsgSource. The LDP peer that sent the Notification message.
- SAttributes. Attributes stored with postponed Label Request mes- - SAttributes. Attributes stored with postponed Label Request
sage. message.
Algorithm: Algorithm:
Res.1 Set status record indicating it is OK to send label requests Res.1 Set status record indicating it is OK to send label requests
to MsgSource. to MsgSource.
Res.2 Iterate through Res.6 for each record of a FEC label mapping Res.2 Iterate through Res.6 for each record of a FEC label mapping
needed from MsgSource for which no label resources are avail- needed from MsgSource for which no label resources are
able. available.
Res.3 Is MsgSource the next hop for FEC? Res.3 Is MsgSource the next hop for FEC?
If not, goto Res.5. If not, goto Res.5.
Res.4 Execute procedure Send_Label_Request (MsgSource, FEC, SAttri- Res.4 Execute procedure Send_Label_Request (MsgSource, FEC,
butes). If the procedure fails, terminate iteration. SAttributes). If the procedure fails, terminate iteration.
Res.5 Delete record that no resources are available for a label Res.5 Delete record that no resources are available for a label
mapping for FEC needed from MsgSource. mapping for FEC needed from MsgSource.
Res.6 End iteration from Res.2 Res.6 End iteration from Res.2
Res.7 DONE. Res.7 DONE.
A.1.11. Detect local label resources have become available A.1.13. Detect local label resources have become available
Summary: Summary:
After an LSR has sent a No Label Resources notification to an LDP After an LSR has sent a No Label Resources notification to an LDP
peer, when label resources later become available it sends a Label peer, when label resources later become available it sends a Label
Resources Available notification to each such peer. Resources Available notification to each such peer.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- Attributes. Attributes stored with postponed Label Mapping mes- - Attributes. Attributes stored with postponed Label Mapping
sage. message.
Algorithm: Algorithm:
ResA.1 Iterate through ResA.4 for each Peer to which LSR has previ- ResA.1 Iterate through ResA.4 for each Peer to which LSR has
ously sent a No Label Resources notification. previously sent a No Label Resources notification.
ResA.2 Execute procedure Send_Notification (Peer, Label Resources ResA.2 Execute procedure Send_Notification (Peer, Label Resources
Available) Available)
ResA.3 Delete record that No Label Resources notification was previ- ResA.3 Delete record that No Label Resources notification was
ously sent to Peer. previously sent to Peer.
ResA.4 End iteration from ResA.1 ResA.4 End iteration from ResA.1
ResA.5 Iterate through ResA.8 for each record of a label mapping ResA.5 Iterate through ResA.8 for each record of a label mapping
needed for FEC for Peer but no-label-resources. (See Note needed for FEC for Peer but no-label-resources. (See Note
1.) 1.)
ResA.6 Execute procedure Send_Label (Peer, FEC, Attributes). If the ResA.6 Execute procedure Send_Label (Peer, FEC, Attributes). If the
procedure fails, terminate iteration. procedure fails, terminate iteration.
skipping to change at page 105, line 4 skipping to change at page 112, line 36
needed for FEC for Peer but no-label-resources. (See Note needed for FEC for Peer but no-label-resources. (See Note
1.) 1.)
ResA.6 Execute procedure Send_Label (Peer, FEC, Attributes). If the ResA.6 Execute procedure Send_Label (Peer, FEC, Attributes). If the
procedure fails, terminate iteration. procedure fails, terminate iteration.
ResA.7 Clear record of FEC label mapping needed for peer but no- ResA.7 Clear record of FEC label mapping needed for peer but no-
label-resources. label-resources.
ResA.8 End iteration from ResA.5 ResA.8 End iteration from ResA.5
ResA.9 DONE. ResA.9 DONE.
Notes: Notes:
1. Iteration ResA.5 through ResA.8 handles the situation where the 1. Iteration ResA.5 through ResA.8 handles the situation where the
LSR is using Downstream Unsolicited label distribution and was LSR is using Downstream Unsolicited label distribution and was
previously unable to allocate a label for a FEC. previously unable to allocate a label for a FEC.
A.1.12. LSR decides to no longer label switch a FEC A.1.14. LSR decides to no longer label switch a FEC
Summary: Summary:
An LSR may unilaterally decide to no longer label switch a FEC for An LSR may unilaterally decide to no longer label switch a FEC for
an LDP peer. An LSR that does so must send a label withdraw message an LDP peer. An LSR that does so must send a label withdraw message
for the FEC to the peer. for the FEC to the peer.
Context: Context:
- Peer. The peer. - Peer. The peer.
- FEC. The FEC. - FEC. The FEC.
- PrevAdvLabel. The label for FEC previously advertised to Peer. - PrevAdvLabel. The label for FEC previously advertised to Peer.
Algorithm: Algorithm:
NoLS.1 Execute procedure Send_Label_Withdraw (Peer, FEC, PrevAdvLa- NoLS.1 Execute procedure Send_Label_Withdraw (Peer, FEC,
bel). (See Note 1.) PrevAdvLabel). (See Note 1.)
NoLS.2 DONE. NoLS.2 DONE.
Notes: Notes:
1. The LSR may remove the label from forwarding/switching use as 1. The LSR may remove the label from forwarding/switching use as
part of this event or as part of processing the label release part of this event or as part of processing the label release
from the peer in response to the label withdraw. from the peer in response to the label withdraw.
A.1.13. Timeout of deferred label request A.1.15. Timeout of deferred label request
Summary: Summary:
Label requests are deferred in response to No Route and Loop Label requests are deferred in response to No Route and Loop
Detected notifications. When a deferred FEC label request for a Detected notifications. When a deferred FEC label request for a
peer times out, the LSR sends the label request. peer times out, the LSR sends the label request.
Context: Context:
- LSR. The LSR handling the event. - LSR. The LSR handling the event.
- FEC. The FEC associated with the timeout event. - FEC. The FEC associated with the timeout event.
- Peer. The LDP peer associated with the timeout event. - Peer. The LDP peer associated with the timeout event.
- Attributes. Attributes stored with deferred Label Request mes- - Attributes. Attributes stored with deferred Label Request
sage. message.
Algorithm: Algorithm:
TO.1 Retrieve the record of the deferred label request. TO.1 Retrieve the record of the deferred label request.
TO.2 Is Peer the next hop for FEC? TO.2 Is Peer the next hop for FEC?
If not, goto TO.4. If not, goto TO.4.
TO.3 Execute procedure Send_Label_Request (Peer, FEC). TO.3 Execute procedure Send_Label_Request (Peer, FEC).
skipping to change at page 108, line 7 skipping to change at page 115, line 40
SL.12 Record No Label Resources notification has been sent to Peer. SL.12 Record No Label Resources notification has been sent to Peer.
Goto SL.14. Goto SL.14.
SL.13 Record label mapping needed for FEC and Attributes for Peer, SL.13 Record label mapping needed for FEC and Attributes for Peer,
but no-label-resources. (See Note 1.) but no-label-resources. (See Note 1.)
SL.14 Return failure. SL.14 Return failure.
Notes: Notes:
1. SL.13 handles the case of Downstream Unsolicited label distri- 1. SL.13 handles the case of Downstream Unsolicited label
bution when the LSR is unable to allocate a label for a FEC to distribution when the LSR is unable to allocate a label for a
send to a Peer. FEC to send to a Peer.
A.2.2. Send_Label_Request A.2.2. Send_Label_Request
Summary: Summary:
An LSR uses the Send_Label_Request procedure to send a request for An LSR uses the Send_Label_Request procedure to send a request for
a label for a FEC to an LDP peer if currently permitted to do so. a label for a FEC to an LDP peer if currently permitted to do so.
Parameters: Parameters:
- Peer. The LDP peer to which the label request is to be sent. - Peer. The LDP peer to which the label request is to be sent.
- FEC. The FEC for which a label request is to be sent. - FEC. The FEC for which a label request is to be sent.
- Attributes. Attributes to be included in the label request. E.g., - Attributes. Attributes to be included in the label request. E.g.,
Hop Count, Path Vector, CoS. Hop Count, Path Vector.
Additional Context: Additional Context:
- LSR. The LSR executing the procedure. - LSR. The LSR executing the procedure.
Algorithm: Algorithm:
SLRq.1 Has a label request for FEC previously been sent to Peer and SLRq.1 Has a label request for FEC previously been sent to Peer and
is it marked as outstanding? is it marked as outstanding?
If so, Return success. (See Note 1.) If so, Return success. (See Note 1.)
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SLRq.6 Postpone the label request by recording label mapping for FEC SLRq.6 Postpone the label request by recording label mapping for FEC
and Attributes from Peer is needed but that no label and Attributes from Peer is needed but that no label
resources are available. resources are available.
SLRq.7 Return failure. SLRq.7 Return failure.
Notes: Notes:
1. If the LSR is a non-merging LSR it must distinguish between 1. If the LSR is a non-merging LSR it must distinguish between
attempts to send label requests for a FEC triggered by dif- attempts to send label requests for a FEC triggered by
ferent upstream LDP peers from duplicate requests. This pro- different upstream LDP peers from duplicate requests. This
cedure will not send a duplicate label request. procedure will not send a duplicate label request.
A.2.3. Send_Label_Withdraw A.2.3. Send_Label_Withdraw
Summary: Summary:
An LSR uses the Send_Label_Withdraw procedure to withdraw a label An LSR uses the Send_Label_Withdraw procedure to withdraw a label
for a FEC from an LDP peer. To do this the LSR sends a Label With- for a FEC from an LDP peer. To do this the LSR sends a Label
draw message to the peer. Withdraw message to the peer.
Parameters: Parameters:
- Peer. The LDP peer to which the label withdraw is to be sent. - Peer. The LDP peer to which the label withdraw is to be sent.
- FEC. The FEC for which a label is being withdrawn. - FEC. The FEC for which a label is being withdrawn.
- Label. The label being withdrawn - Label. The label being withdrawn
Additional Context: Additional Context:
skipping to change at page 110, line 48 skipping to change at page 118, line 38
Algorithm: Algorithm:
This procedure is the means by which an LSR sends an LDP message of This procedure is the means by which an LSR sends an LDP message of
the specified type to the specified LDP peer. the specified type to the specified LDP peer.
A.2.6. Check_Received_Attributes A.2.6. Check_Received_Attributes
Summary: Summary:
Check the attributes received in a Label Mapping or Label Request Check the attributes received in a Label Mapping or Label Request
message. If the attributes include a Hop Count or Path Vector, per- message. If the attributes include a Hop Count or Path Vector,
form a loop detection check. If a loop is detected, send a Loop perform a loop detection check. If a loop is detected, send a Loop
Detected Notification message to MsgSource. Detected Notification message to MsgSource.
Parameters: Parameters:
- MsgSource. The LDP peer that sent the message. - MsgSource. The LDP peer that sent the message.
- RAttributes. The attributes in the message. - RAttributes. The attributes in the message.
Additional Context: Additional Context:
skipping to change at page 113, line 8 skipping to change at page 121, line 4
PRqA.8 Include Hop Count of unknown (0) in SAttributes. PRqA.8 Include Hop Count of unknown (0) in SAttributes.
PRqA.9 Is Loop Detection configured on LSR? PRqA.9 Is Loop Detection configured on LSR?
If not, goto PRqA.14. If not, goto PRqA.14.
PRqA.10 Do RAttributes have a Path Vector? PRqA.10 Do RAttributes have a Path Vector?
If so, goto PRqA.12. If so, goto PRqA.12.
PRqA.11 Is LSR merge-capable? PRqA.11 Is LSR merge-capable?
If so, goto PRqA.14. If so, goto PRqA.14.
If not, goto PRqA.13. If not, goto PRqA.13.
PRqA.12 Add LSR Id to beginning of Path Vector from RAttributes and PRqA.12 Add LSR Id to beginning of Path Vector from RAttributes and
copy the resulting Path Vector into SAttributes. copy the resulting Path Vector into SAttributes.
Goto PRqA.14. Goto PRqA.14.
PRqA.13 Include Path Vector of length 1 containing LSR Id in SAttri- PRqA.13 Include Path Vector of length 1 containing LSR Id in
butes. SAttributes.
PRqA.14 DONE. PRqA.14 DONE.
Notes: Notes:
1. The link with Peer may require that Hop Count be included in 1. The link with Peer may require that Hop Count be included in
Label Request messages; for example, see [ATM] and [FR]. Label Request messages; for example, see [ATM] and [FR].
2. For hop count arithmetic, unknown + 1 = unknown. 2. For hop count arithmetic, unknown + 1 = unknown.
skipping to change at page 115, line 25 skipping to change at page 123, line 22
If not goto PMpA.21. If not goto PMpA.21.
PMpA.18 Is the Hop Count in RAttributes > PrevHopCount? OR PMpA.18 Is the Hop Count in RAttributes > PrevHopCount? OR
Is PrevHopCount unknown(0) Is PrevHopCount unknown(0)
If not, goto PMpA.21. If not, goto PMpA.21.
PMpA.19 Add LSR Id to beginning of Path Vector from RAttributes and PMpA.19 Add LSR Id to beginning of Path Vector from RAttributes and
copy the resulting Path Vector into SAttributes. Goto copy the resulting Path Vector into SAttributes. Goto
PMpA.21. PMpA.21.
PMpA.20 Include Path Vector of length 1 containing LSR Id in SAttri- PMpA.20 Include Path Vector of length 1 containing LSR Id in
butes. SAttributes.
PMpA.21 DONE. PMpA.21 DONE.
Notes: Notes:
1. The link with Peer may require that Hop Count be included in 1. The link with Peer may require that Hop Count be included in
Label Mapping messages; for example, see [ATM] and [FR]. Label Mapping messages; for example, see [ATM] and [FR].
2. If the LSR is at the edge of a cloud of LSRs that do not per- 2. If the LSR is at the edge of a cloud of LSRs that do not
form TTL-decrement and it is propagating the Label Mapping mes- perform TTL-decrement and it is propagating the Label Mapping
sage upstream into the cloud, it sets the Hop Count to 1 so message upstream into the cloud, it sets the Hop Count to 1 so
that Hop Count across the cloud is calculated properly. This that Hop Count across the cloud is calculated properly. This
ensures proper TTL mamagement for packets forwarded across the ensures proper TTL management for packets forwarded across the
part of the LSP that passes through the cloud. part of the LSP that passes through the cloud.
3. For hop count arithmetic, unknown + 1 = unknown. 3. For hop count arithmetic, unknown + 1 = unknown.
 End of changes. 

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