draft-ietf-mpls-ldp-01.txt   draft-ietf-mpls-ldp-02.txt 
Network Working Group Loa Andersson Network Working Group Loa Andersson
Internet Draft Bay Networks Inc. Internet Draft Nortel Networks Inc.
Expiration Date: February 1999 Expiration Date: May 1999
Paul Doolan Paul Doolan
Ennovate Networks Ennovate Networks
Nancy Feldman Nancy Feldman
IBM Corp IBM Corp
Andre Fredette Andre Fredette
Bay Networks Inc. Nortel Networks Inc.
Bob Thomas Bob Thomas
Cisco Systems, Inc. Cisco Systems, Inc.
August 1998 November 1998
LDP Specification LDP Specification
draft-ietf-mpls-ldp-01.txt draft-ietf-mpls-ldp-02.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
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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 the
Label Distribution Protocol (LDP) referenced in [FRAMEWORK] and Label Distribution Protocol (LDP) referenced in [ARCH]. This
[ARCH]. This document defines the LDP protocol. document defines the LDP protocol.
Open Issues Changes from Previous Draft
The following LDP issues are left unresolved with this version of the - This draft removes the explicit path setup mechanism from the
spec: spec.
- The loop prevention/detection mechanism to be employed by LDP. - This draft removes loop prevention from the spec. The MPLS
This spec has retained the path vector mechanism from previous working group will continue to evaluate and compare the two
drafts. However, draft-ohba-mpls-loop-prevention-01.txt has been leading contenders for loop prevention: loop prevention via path
proposed as an alternative. vectors and draft-ohba-mpls-loop-prevention-01.txt. We expect
that one of these methods will be selected and added to a later
version of LDP.
- Support for explicitly routed LSPs. The need for this feature - This draft retains and refines the path vector mechanism for
has been debated at length. This spec refines the previous optional loop detection. In addition, it introduces an upper
version of the spec in this area. However, there remains some limit on the size of path vectors.
belief in the WG that explicitly routed LSPs should be supported
by enhancements to RSVP and not LDP.
The support for explicitly routed LSPs in the spec is independent - This draft specifies parameters for the exponential backup used
of other LDP features and could, should the WG decide to do so, to throttle session setup retry attempts. It also specifies a
be removed without impact on other LDP features. mechanism for resetting the backoff parameters in response to LSR
configuration changes by adding an optional parameter to the
Hello message.
- Traffic engineering considerations beyond support for explicit - This draft adds Appendix "LDP Label Distribution Procedures".
routing.
- The need for all of the FEC types (called FEC elements in this - This draft adds rules for resolving differences in the Label
version of the spec, SMDs in previous versions) is being debated. Distribution Discipline and Merge session parameters exchanged in
This version of the spec defines fewer FEC types than previous the Initialization message.
versions.
- LDP support for multicast is not defined in this version. - This draft modifies message and TLV encodings slightly by adding
explicit specification of LSR behavior when an LSR does not
recognize the message or TLV.
- This draft modifies the encodings for the Initialization and
Hello messages to group parameters likely to be used together and
to reduce message sizes. It defines some new TLVs for use with
these messages and eliminates some previously defined TLVs.
- This draft specifies a procedure for negotiating the maximum PDU
length to be used for a session.
- This draft simplifies the encodings for the Label Mapping, Label
Request, Label Withdraw and Label Release messages by eliminating
the FEC-Label Mapping, FEC-Request, and FEC-Withdraw-Release
TLVs.
- This draft modifies the CoS TLV by specifying that its detailed
definition is a subject for further study.
- This draft adds a Return Message Id optional parameter to the
Label Request message and a Label Request Message Id parameter to
the Label Mapping message to enable an LSR to match received
Label Mapping messages with outstanding Label Request messages.
- This draft refines support for vendor-private protocol extensions
and specifies support for experimental protocol extensions.
- This draft specifies optional use of the TCP MD5 Signature Option
to protect against the introduction of spoofed TCP segments into
LDP session connection streams.
Open Issues
The following LDP issues are left unresolved with this version of the
spec:
- LDP support for CoS is not completely specified in this version.
Cos support will be more fully addressed in a future 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.
- The message and TLV encodings are likely to change in some minor - LDP support for multipath label switching is not specified in
ways in the next draft of the spec. this version. Multipath support will be addressed in a future
version.
Table of Contents Table of Contents
1 LDP Overview ....................................... 6 1 LDP Overview ....................................... 7
1.1 LDP Peers .......................................... 6 1.1 LDP Peers .......................................... 7
1.2 LDP Message Exchange ............................... 6 1.2 LDP Message Exchange ............................... 7
1.3 LDP Error Handling ................................. 7 1.3 LDP Message Structure .............................. 8
1.4 LDP Extensibility and Future Compatibility ......... 8 1.4 LDP Error Handling ................................. 8
2 LDP Operation ...................................... 8 1.5 LDP Extensibility and Future Compatibility ......... 9
2.1 FEC Types .......................................... 8 2 LDP Operation ...................................... 9
2.2 Mapping packets to FECs ........................... 9 2.1 FECs ............................................... 9
2.3 Label Spaces, Identifiers, Sessions and Transport .. 10 2.2 Label Spaces, Identifiers, Sessions and Transport .. 10
2.4 LDP Sessions between non-Directly Connected LSRs ... 11 2.2.1 Label Spaces ....................................... 10
2.5 LDP Discovery ..................................... 12 2.2.2 LDP Identifiers .................................... 11
2.5.1 Basic Discovery Mechanism .......................... 12 2.2.3 LDP Sessions ....................................... 11
2.5.2 Extended Discovery Mechanism ....................... 12 2.2.4 LDP Transport ...................................... 11
2.6 Establishing and Maintaining LDP Sessions .......... 13 2.3 LDP Sessions between non-Directly Connected LSRs ... 12
2.6.1 LDP Session Establishment .......................... 13 2.4 LDP Discovery ..................................... 12
2.6.2 Transport Connection Establishment ................. 13 2.4.1 Basic Discovery Mechanism .......................... 12
2.6.3 Session Initialization ............................. 14 2.4.2 Extended Discovery Mechanism ....................... 13
2.6.4 Initialization State Machine ....................... 16 2.5 Establishing and Maintaining LDP Sessions .......... 14
2.6.5 Maintaining Hello Adjacencies ...................... 19 2.5.1 LDP Session Establishment .......................... 14
2.6.6 Maintaining LDP Sessions ........................... 19 2.5.2 Transport Connection Establishment ................. 14
2.7 Label Distribution and Management .................. 20 2.5.3 Session Initialization ............................. 15
2.7.1 Label Distribution Control Mode .................... 20 2.5.4 Initialization State Machine ....................... 17
2.7.2 Label Retention Mode ............................... 21 2.5.5 Maintaining Hello Adjacencies ...................... 20
2.7.3 Label Advertisement Mode ........................... 22 2.5.6 Maintaining LDP Sessions ........................... 20
2.8 LDP Identifiers and Next Hop Addresses ............. 22 2.6 Label Distribution and Management .................. 21
2.9 Loop Detection ..................................... 22 2.6.1 Label Distribution Control Mode .................... 21
2.10 Loop Prevention via Diffusion ...................... 23 2.6.1.1 Independent Label Distribution Control ............. 21
2.11 Explicitly Routing LSPs ............................ 24 2.6.1.2 Ordered Label Distribution Control ................. 21
2.12 ERLSP State Machine ................................ 28 2.6.2 Label Retention Mode ............................... 22
2.12.1 Loose Segment Peg LSR Transitions: ................. 29 2.6.2.1 Conservative Label Retention Mode .................. 22
2.12.2 Loose Segment Non-Peg LSR Transitions: ............. 33 2.6.2.2 Liberal Label Retention Mode ....................... 22
2.12.2.1 Strict Segment Transitions ......................... 35 2.6.3 Label Advertisement Mode ........................... 23
2.12.3 ERLSP Timeouts ..................................... 35 2.7 LDP Identifiers and Next Hop Addresses ............. 23
2.12.4 ERLSP Error Codes .................................. 35 2.8 Loop Detection ..................................... 24
3 Protocol Specification ............................. 36 2.8.1 Label Request Message .............................. 24
3.1 LDP PDUs ........................................... 36 2.8.2 Label Mapping Message .............................. 26
3.2 Type-Length-Value Encoding ......................... 37 2.8.3 Discussion ......................................... 27
3.3 Commonly Used TLVs ................................. 38 3 Protocol Specification ............................. 28
3.3.1 FEC TLV ............................................ 38 3.1 LDP PDUs ........................................... 28
3.3.1.1 FEC Procedures ..................................... 41 3.2 LDP Procedures ..................................... 29
3.3.2 Label TLVs ......................................... 41 3.3 Type-Length-Value Encoding ......................... 30
3.3.2.1 Generic Label TLV .................................. 42 3.4 TLV Encodings for Commonly Used Parameters ......... 31
3.3.2.2 ATM Label TLV ...................................... 42 3.4.1 FEC TLV ............................................ 31
3.3.2.3 Frame Relay Label TLV .............................. 43 3.4.1.1 FEC Procedures ..................................... 34
3.3.3 Address List TLV ................................... 43 3.4.2 Label TLVs ......................................... 34
3.3.4 COS TLV ............................................ 44 3.4.2.1 Generic Label TLV .................................. 34
3.3.5 Hop Count TLV ...................................... 45 3.4.2.2 ATM Label TLV ...................................... 34
3.3.5.1 Hop Count Procedures ............................... 45 3.4.2.3 Frame Relay Label TLV .............................. 35
3.3.6 Path Vector TLV .................................... 46 3.4.3 Address List TLV ................................... 36
3.3.6.1 Path Vector Procedures ............................. 46 3.4.4 COS TLV ............................................ 37
3.3.7 Status TLV ......................................... 47 3.4.5 Hop Count TLV ...................................... 37
3.4 LDP Messages ....................................... 48 3.4.5.1 Hop Count Procedures ............................... 38
3.4.1 Notification Message ............................... 50 3.4.6 Path Vector TLV .................................... 38
3.4.1.1 Notification Message Procedures .................... 51 3.4.6.1 Path Vector Procedures ............................. 39
3.4.1.2 Events Signalled by Notification Messages .......... 51 3.4.6.1.1 Label Request Path Vector .......................... 39
3.4.1.2.1 Malformed PDU or Message ........................... 52 3.4.6.1.2 Label Mapping Path Vector .......................... 40
3.4.1.2.2 Unknown or Malformed TLV ........................... 52 3.4.7 Status TLV ......................................... 40
3.4.1.2.3 Session Hold Timer Expiration ...................... 53 3.5 LDP Messages ....................................... 42
3.4.1.2.4 Unilateral Session Shutdown ........................ 53 3.5.1 Notification Message ............................... 44
3.4.1.2.5 Initialization Message Events ...................... 53 3.5.1.1 Notification Message Procedures .................... 45
3.4.1.2.6 Events Resulting From Other Messages ............... 54 3.5.1.2 Events Signaled by Notification Messages ........... 45
3.4.1.2.7 Explicitly Routed LSP Setup Events ................. 54 3.5.1.2.1 Malformed PDU or Message ........................... 46
3.4.1.2.8 Miscellaneous Events ............................... 54 3.5.1.2.2 Unknown or Malformed TLV ........................... 46
3.4.2 Hello Message ...................................... 54 3.5.1.2.3 Session Hold Timer Expiration ...................... 47
3.4.2.1 Hello Message Procedures ........................... 55 3.5.1.2.4 Unilateral Session Shutdown ........................ 47
3.4.3 Initialization Message ............................. 57 3.5.1.2.5 Initialization Message Events ...................... 47
3.4.3.1 Initialization Message Procedures .................. 61 3.5.1.2.6 Events Resulting From Other Messages ............... 47
3.4.4 KeepAlive Message .................................. 61 3.5.1.2.7 Miscellaneous Events ............................... 48
3.4.4.1 KeepAlive Message Procedures ....................... 62 3.5.2 Hello Message ...................................... 48
3.4.5 Address Message .................................... 62 3.5.2.1 Hello Message Procedures ........................... 50
3.4.5.1 Address Message Procedures ......................... 63 3.5.3 Initialization Message ............................. 51
3.4.6 Address Withdraw Message ........................... 64 3.5.3.1 Initialization Message Procedures .................. 58
3.4.6.1 Address Withdraw Message Procedures ................ 64 3.5.4 KeepAlive Message .................................. 59
3.4.7 Label Mapping Message .............................. 64 3.5.4.1 KeepAlive Message Procedures ....................... 59
3.4.7.1 Label Mapping Message Procedures ................... 66 3.5.5 Address Message .................................... 59
3.4.7.1.1 Independent Control Mapping ........................ 66 3.5.5.1 Address Message Procedures ......................... 60
3.4.7.1.2 Ordered Control Mapping ............................ 67 3.5.6 Address Withdraw Message ........................... 61
3.4.7.1.3 Downstream-on-Demand Label Advertisement ........... 67 3.5.6.1 Address Withdraw Message Procedures ................ 61
3.4.7.1.4 Downstream Allocation Label Advertisement .......... 68 3.5.7 Label Mapping Message .............................. 61
3.4.8 Label Request Message .............................. 68 3.5.7.1 Label Mapping Message Procedures ................... 63
3.4.8.1 Label Request Message Procedures ................... 69 3.5.7.1.1 Independent Control Mapping ........................ 63
3.4.9 Label Withdraw Message ............................. 70 3.5.7.1.2 Ordered Control Mapping ............................ 64
3.4.9.1 Label Withdraw Message Procedures .................. 71 3.5.7.1.3 Downstream-on-Demand Label Advertisement ........... 64
3.4.10 Label Release Message .............................. 72 3.5.7.1.4 Downstream Unsolicited Label Advertisement ......... 65
3.4.10.1 Label Release Message Procedures ................... 73 3.5.8 Label Request Message .............................. 65
3.4.11 Label Query Message ................................ 73 3.5.8.1 Label Request Message Procedures ................... 66
3.4.11.1 Label Query Message Procecures ..................... 74 3.5.9 Label Withdraw Message ............................. 67
3.4.12 Explicit Route Request Message ..................... 74 3.5.9.1 Label Withdraw Message Procedures .................. 68
3.4.12.1 Explicit Route Request Procedures .................. 78 3.5.10 Label Release Message .............................. 69
3.4.13 Explicit Route Response Message .................... 78 3.5.10.1 Label Release Message Procedures ................... 70
3.4.13.1 Explicit Route Response Procedures ................. 79 3.6 Messages and TLVs for Extensibility ................ 71
3.5 Messages and TLVs for Extensibility ................ 80 3.6.1 LDP Vendor-private Extensions ...................... 71
3.5.1 Procedures for Unknown Messages and TLVs ........... 80 3.6.1.1 LDP Vendor-private TLVs ............................ 71
3.5.1.1 Unknown Message Types .............................. 80 3.6.1.2 LDP Vendor-private Messages ........................ 72
3.5.1.2 Unknown TLV in Known Message Type .................. 80 3.6.2 LDP Experimental Extensions ........................ 74
3.5.2 LDP Vendor-Private Extensions ...................... 81 3.7 Message Summary .................................... 74
3.5.2.1 LDP Vendor-Private TLV ............................. 81 3.8 TLV Summary ........................................ 75
3.5.2.2 LDP Vendor-Private Messages ........................ 82 3.9 Status Code Summary ................................ 76
3.6 TLV Summary ........................................ 83 3.10 UDP and TCP Ports .................................. 76
3.7 Status Code Summary ................................ 84 4 Security ........................................... 77
4 Security ........................................... 84 4.1 The TCP MD5 Signature Option ....................... 77
5 Acknowledgments .................................... 84 4.2 LDP Use of the TCP MD5 Signature Option ............ 78
6 References ......................................... 84 5 Intellectual Property Considerations ............... 79
7 Author Information ................................. 85 6 Acknowledgments .................................... 79
7 References ......................................... 79
8 Author Information ................................. 80
Appendix.A LDP Label Distribution Procedures .................. 82
A.1 Handling Label Distribution Events ................. 84
A.1.1 Receive Label Request .............................. 85
A.1.2 Receive Label Mapping .............................. 88
A.1.3 Receive Label Release .............................. 92
A.1.4 Receive Label Withdraw ............................. 94
A.1.5 Recognize New FEC .................................. 95
A.1.6 Detect change in FEC next hop ...................... 98
A.1.7 Receive Notification / No Label Resources .......... 100
A.1.8 Receive Notification / No Route .................... 101
A.1.9 Receive Notification / Loop Detected ............... 102
A.1.10 Receive Notification / Label Resources Available ... 102
A.1.11 Detect local label resources have become available . 103
A.1.12 LSR decides to no longer label switch a FEC ........ 104
A.1.13 Timeout of deferred label request .................. 104
A.2 Common Label Distribution Procedures ............... 105
A.2.1 Send_Label ......................................... 105
A.2.2 Send_Label_Request ................................. 107
A.2.3 Send_Label_Withdraw ................................ 108
A.2.4 Send_Notification .................................. 108
A.2.5 Send_Message ....................................... 109
A.2.6 Check_Received_Attributes .......................... 109
A.2.7 Prepare_Label_Request_Attributes ................... 110
A.2.8 Prepare_Label_Mapping_Attributes ................... 112
1. LDP Overview 1. LDP Overview
LDP is the set of procedures and messages by which Label Switched LDP is the set of procedures and messages by which Label Switched
Routers (LSRs) establish Label Switched Paths (LSPs) through a Routers (LSRs) establish Label Switched Paths (LSPs) through a
network by mapping network-layer routing information directly to network by mapping network-layer routing information directly to
data-link layer switched paths. These LSPs may have an endpoint at a data-link layer switched paths. These LSPs may have an endpoint at a
directly attached neighbor (comparable to IP hop-by-hop forwarding), directly attached neighbor (comparable to IP hop-by-hop forwarding),
or may have an endpoint at a network egress node, enabling switching or may have an endpoint at a network egress node, enabling switching
via all intermediary nodes. 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 Note that this document is written with respect to unicast routing
only. Multicast will be addressed in a future revision. only. Multicast will be addressed in a future revision.
Note that this document is written with respect to control-driven
traffic. It describes mappings which are initiated for routes in the
forwarding table, regardless of traffic over those routes. However,
LDP does not preclude data-driven support.
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
adjacency 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
There are four categories of LDP messages: There are four categories of LDP messages:
1. Discovery messages, used to announce and maintain the presence 1. Discovery messages, used to announce and maintain the presence
of an LSR in a network. of an LSR in a network.
2. Session messages, used to establish and maintain terminate 2. Session messages, used to establish, maintain, and terminate
sessions between LSR peers. sessions between LDP peers.
3. Advertisement messages, used to create, change, and delete 3. Advertisement messages, used to create, change, and delete
label mappings for FECs. label mappings for FECs.
4. Notification messages, used to provide advisory information and 4. Notification messages, used to provide advisory information and
to signal errors. to signal error information.
Discovery messages provide a mechanism whereby LSRs continually Discovery messages provide a mechanism whereby LSRs indicate their
indicate their presence in a network via the Hello message. This is presence in a network by sending the Hello message periodically.
transmitted as a UDP packet to the LDP port at the `all LSR routers' This is transmitted as a UDP packet to the LDP port at the `all
group multicast address. When an LSR chooses to establish a session routers' group multicast address. When an LSR chooses to establish a
with an LSR learned via the hello message, it uses the LDP session with another LSR learned via the Hello message, it uses the
initialization procedure over TCP transport. Upon successful LDP initialization procedure over TCP transport. Upon successful
completion of the initialization procedure, the two LSRs are LDP completion of the initialization procedure, the two LSRs are LDP
peers, and may exchange advertisement messages. peers, and may exchange advertisement messages.
When to request a label or advertise a label mapping to a peer is When to request a label or advertise a label mapping to a peer is
largely a local decision made by an LSR. In general, the LSR largely a local decision made by an LSR. In general, the LSR
requests a label mapping from a neighboring LSR when it needs one, requests a label mapping from a neighboring LSR when it needs one,
and advertises a label mapping to a neighboring LSR when it wishes and advertises a label mapping to a neighboring LSR when it wishes
the neighbor to use a label. the neighbor to use a label.
Correct operation of LDP requires reliable and in order delivery of Correct operation of LDP requires reliable and in order delivery of
mappings (although there are circumstances when this second messages. To satisfy these requirements LDP uses the TCP transport
requirement could be relaxed). To satisfy these requirements LDP uses for session, advertisement and notification messages; i.e., for
the TCP transport for adjacency, advertisement and notification everything but the UDP-based discovery mechanism.
messages.
1.3. LDP Error Handling 1.3. LDP Message Structure
LDP errors and other events of interest are signaled to an LSR peer All LDP messages have a common structure that uses a Type-
Length_Value (TLV) encoding scheme; see Section "Type-Length-Value"
encoding. The Value part of a TLV-encoded object, or TLV for short,
may itself contain one or more TLVs.
1.4. LDP Error Handling
LDP errors and other events of interest are signaled to an LDP peer
by notification messages. by notification messages.
There are two kinds of LDP notification messages: There are two kinds of LDP notification messages:
1. Error notifications, used to signal fatal errors. If an LSR 1. Error notifications, used to signal fatal errors. If an LSR
receives an error notification for an LDP session with a peer, receives an error notification from a peer for an LDP session,
it terminates the peer session by closing the TCP transport it terminates the LDP session by closing the TCP transport
connection for the session and discarding all label mappings connection for the session and discarding all label mappings
learned via the session. learned via the session.
2. Advisory notifications, used to pass an LSR information about 2. Advisory notifications, used to pass an LSR information about
the LDP session or the status of some previous message received the LDP session or the status of some previous message received
from the peer. from the peer.
1.4. LDP Extensibility and Future Compatibility 1.5. LDP Extensibility and Future Compatibility
It is likely that functionality will be added to LDP after its Functionality may be added to LDP in the future. It is likely that
initial release. It is also likely that this additional future functionality will utilize new messages and object types
functionality will utilize new messages and object types (TLVs). It (TLVs). It may be desirable to employ such new messages and TLVs
may be desirable to employ such new messages and TLVs within a within a network using older implementations that do not recognize
network using older implementations that do not recognize them. them. While it is not possible to make every future enhancement
While it is not possible to make every future enhancement backwards backwards compatible, some prior planning can ease the introduction
compatible, some prior planning can ease the introduction of new of new capabilities. This specification defines rules for handling
capabilities. This specification defines rules for handling unknown unknown message types and unknown TLVs for this purpose.
message types and unknown TLVs for this purpose.
2. LDP Operation 2. LDP Operation
2.1. FEC Types 2.1. FECs
It is necessary to precisely define which IP packets may be mapped to
each LSP. This is done by providing a FEC specification for each LSP.
The FEC defines which IP packets may be mapped to the same LSP, using
a unique label.
LDP supports LSP granularity ranging from end-to-end flows to the It is necessary to precisely specify which IP packets may be mapped
aggregation of all traffic through a common egress node; the choice to each LSP. This is done by providing a FEC specification for each
of granularity is determined by the FEC choice. LSP. The FEC identifies the set of IP packets which may be mapped to
that LSP.
Each FEC is specified as a list of one or more FEC elements. Each FEC Each FEC is specified as a set of one or more FEC elements. Each FEC
element specifies a set of IP packets which may be mapped to the element identifies a set of IP packets which may be mapped to the
corresponding LSP. corresponding LSP. When an LSP is shared by multiple FEC elements,
that LSP is terminated at (or before) the node where the FEC elements
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. 1. IP Address Prefix. This element is an IP address prefix of any
length from 0 to 32 bits, inclusive.
This element provides a list of one or more IP address
prefixes. Any IP packet whose destination address matches one
or more of the specified prefixes may be forwarded using the
associated LSP.
2. Router ID
This element provides a Router ID (ie, a 32 bit IP address of a
router). Any IP packet for which the path to the destination is
known to traverse the specified router may be forwarded using
the associated LSP. This element allows the full set of
destinations reachable via a specified router to be indicated
in a single FEC element.
3. Flow 2. Host Address. This element is a 32-bit IP address.
This element specifies a set of datagram information, such as We say that a particular IP address "matches" a particular IP address
port, dest-addr, src-addr, etc. This element provides LDP with prefix if and only if that address begins with that prefix. We also
the ability to support MPLS flows with no aggregation. 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
packet's IP destination address. With respect to a particular packet
and a particular LSP, we refer to any IP Address Prefix FEC element
which matches the packet as the "matching prefix".
Where a packet maps to more than one FEC it is transmitted on the LSP The procedure for mapping a particular packet to a particular LSP
associated with the FEC to which the packet has the 'most specific' uses the following rules. Each rule is applied in turn until the
match. packet can be mapped to an LSP.
2.2. Mapping packets to FECs - If there is exactly one LSP which has a Host Address FEC element
that is identical to the packet's IP destination address, then
the packet is mapped to that LSP.
FEC objects (TLVs) are transmitted in the LDP messages that deal with - If there multiple LSPs, each containing a Host Address FEC
(advertise, request, release ad withdraw) FEC-Label mappings. element that is identical to the packet's IP destination address,
then the packet is mapped to one of those LSPs. The procedure
for selecting one of those LSPs is beyond the scope of this
document.
A stream of packets with a given destination network can be - If a packet matches exactly one LSP, the packet is mapped to that
characterized by a single Address Prefix FEC Element. This results LSP.
in each specified address prefix sustaining its own LSP tree. This
singular mapping is recommended in environments where little or no
aggregation information is provided by the routing protocols (such as
within a simple IGP), or in networks where the number of destination
prefixes is limited.
In environments where additional aggregation not provided by the - If a packet matches multiple LSPs, it is mapped to the LSP whose
routing protocols is desired, an aggregation list may be created. In matching prefix is the longest. If there is no one LSP whose
this, all prefixes that are to share a common egress point may be matching prefix is longest, the packet is mapped to one of those
advertised within the same FEC. This type of aggregation is LSPs. The procedure for selecting one of those LSPs is beyond
configured. the scope of this document.
The router ID FEC type may be used in any environment in which the - If it is known that a packet must traverse a particular egress
routing protocols allow routers to determine the egress point for router, and there is an LSP which has an IP Address Prefix FEC
specific IP packets. For example, the router ID FEC type may be used element (of length 32 bits) which is an address of that router,
in combination with BGP, OSPF, and/or IS-IS. then the packet is mapped to that LSP. The procedure for
obtaining this knowledge is beyond the scope of this document.
For example, the mapping between IP packets and the router ID may be 2.2. Label Spaces, Identifiers, Sessions and Transport
provided via the BGP NEXT_HOP attribute. When a BGP border LSR
injects routes into the BGP mesh, it may use its own IP address or
the address of its external BGP peer as the value of the NEXT_HOP
attribute. If the BGP border ISR uses its own IP address as the
NEXT_HOP attribute, then one LSP is created which terminates at the
BGP border, and the border LSR will forward traffic at layer-3
towards its external BGP neighbors. If the BGP border LSR uses the
external BGP peer as the NEXT_HOP attribute, then a separate LSP may
be created for each external BGP neighbor, thereby allowing the
border LSR to switch traffic directly to each of its external BGP
neighbors.
Similarly, the mapping between IP packet and router ID may be 2.2.1. Label Spaces
provided by OSPF. This is comprised of the Router ID of the router
that initiated the link state advertisement. The Router ID may also
be the OSPF Area Border Router.
Note that BGP and OSPF may share the same LSP when a given Router ID The notion of "label space" is useful for discussing the assignment
is found in both protocol's Routing Information Base. and distribution of labels. There are two types of label spaces:
The Router ID FEC allows aggregation of multiple IP address prefixes - Per interface label space. Interface-specific incoming labels
to the same LSP, without requiring that the prefixes be explicitly are used for interfaces that use interface resources for labels.
listed in the FEC. Also, it allows addresses advertised using OSPF An example of such an interface is a label-controlled ATM
and addresses advertised using BGP to be aggregated using the same interface that uses VCIs as labels, or a Frame Relay interface
LSP. Finally, when the set of addresses reachable via a router that uses DLCIs as labels.
changes, and the changes are announced into the routing protocol
(BGP, OSPF, and/or IS-IS), use of the routerID FEC eliminates the
need to explicitly announce the route changes into LDP.
2.3. Label Spaces, Identifiers, Sessions and Transport Note that the use of a per interface label space only makes sense
when the LDP peers are "directly connected" over an interface,
and the label is only going to be used for traffic sent over that
interface.
The notion of "label space" is useful for discussing the assignment - Per platform label space. Platform-wide incoming labels are used
and distribution of labels. There are two types of label spaces: for interfaces that can share the same labels.
- Per interface label space. Interface-specific incoming 2.2.2. LDP Identifiers
labels are used for interfaces that use interface resources
for labels. An example of such an interface is a label-
controlled ATM interface which uses VCIs as labels, or a
frame Relay interface which uses DLCIs as labels.
Note that the use of a per interface label space only makes An LDP identifier is a six octet quantity used to identify an LSR
sense when the LDP peers are "directly connected" over an label space. The first four octets encode an IP address assigned to
interface, and the label is only going to be used for the LSR, and the last two octets identify a specific label space
traffic sent over that interface. within the LSR. The last two octets of LDP Identifiers for
platform-wide label spaces are always both zero. This document uses
the following print representation for LDP Identifiers:
- Per platform label space. Platform-wide incoming labels are <IP address> : <label space id>
used for interfaces that can share the same labels.
An LDP identifier is a six octet quantity used to identify an e.g., 171.32.27.28:0, 192.0.3.5:2.
LSR label space. The first four octets encode an IP address
assigned to the LSR, and the last two octets identify a specific
label space within the LSR. The last two octets of LDP Identif-
iers for platform-wide label spaces are always both zero. This
document uses the following print representation for LDP Iden-
tifiers:
<IP address> : <Label space Id> Note that an LSR that manages and advertises multiple label spaces
uses a different LDP Identifier for each such label space.
for example, 171.32.27.28:0, 192.0.3.5:2. A situation where an LSR would need to advertise more than one label
space to a peer and hence use more than one LDP Identifier occurs
when the LSR has two links to the peer and both are ATM (and use per
interface labels). Another situation would be where the LSR had two
links to the peer, one of which is ethernet (and uses per platform
labels) and the other of which is ATM.
Note that an LSR that manages and advertises more than one label 2.2.3. LDP Sessions
space uses a different LDP Identifier for each such label space.
A situation where an LSR would need to advertise more than one LDP sessions exist between LSRs to support label exchange between
label space to a peer and hence use more than one LDP Identifier them.
occurs when the LSR has two links to the peer and both are ATM
(and use per interface labels). Another situation would be
where the LSR had two links to the peer, one of which is ether-
net (and uses per platform lables) and the other of which is
ATM.
LDP sessions exist between LSRs to support label exchange When an LSR uses LDP to advertise more than one label space to
between them. another LSR it uses a separate LDP session for each label space.
When a LSR must use LDP to advertise more than one label 2.2.4. LDP Transport
space to another LSR it uses a separate LDP session for each
label space rather than a single LDP session for all the
label spaces.
LDP uses TCP as a reliable transport for sessions. LDP uses TCP as a reliable transport for sessions.
When multiple LDP sessions are required between two platforms When multiple LDP sessions are required between two LSRs there is
there is one LDP session per TCP connection rather than many one TCP session for each LDP session.
LDP sessions per TCP connection.
2.4. LDP Sessions between non-Directly Connected LSRs 2.3. LDP Sessions between non-Directly Connected LSRs
LDP sessions between LSRs that are not directly connected at the link LDP sessions between LSRs that are not directly connected at the link
level may be desirable in some situations. level may be desirable in some situations.
For example, consider a "traffic engineering" application where LSR For example, consider a "traffic engineering" application where LSRa
LSR1 sends traffic matching some criteria via an LSP to non-directly sends traffic matching some criteria via an LSP to non-directly
connected LSR LSR2 rather than forwarding the traffic along its nor- connected LSRb rather than forwarding the traffic along its normally
mally routed path. routed path.
An LDP session between LSR1 and LSR2 enables LSR2 to label switch The path between LSRa and LSRb would include one or more intermediate
traffic arriving on the LSP from LSR1. In this situation LSR1 LSRs (LSR1,...LSRn). An LDP session between LSRa and LSRb would
applies two labels to traffic it forwards on the LSP. First, it adds enable LSRb to label switch traffic arriving on the LSP from LSRa by
the label learned via the LDP session with LSR2 to the packet label providing LSRb means to advertise labels for this purpose to LSRa.
stack (either by replacing the label on top of the packet label stack
with it if the packet arrives labeled or by pushing it if the packet
arrives unlabeled). Next, it pushes the label for the LSP onto the
label stack.
2.5. LDP Discovery In this situation LSRa would apply two labels to traffic it forwards
on the LSP to LSRb: a label learned from LSR1 to forward traffic
along the LSP path from LSRa to LSRb; and a label learned from LSRb
to enable LSRb to label switch traffic arriving on the LSP.
LDP discovery is a mechanism that enables an LSR to discover poten- LSRa first adds the label learned via its LDP session with LSRb to
tial LDP peers. Discovery makes it unnecessary to explicitly config- the packet label stack (either by replacing the label on top of the
ure an LSR's label switching peers. packet label stack with it if the packet arrives labeled or by
pushing it if the packet arrives unlabeled). Next, it pushes the
label for the LSP learned from LSR1 onto the label stack.
2.4. LDP Discovery
LDP discovery is a mechanism that enables an LSR to discover
potential LDP peers. Discovery makes it unnecessary to explicitly
configure an LSR's label switching peers.
There are two variants of the discovery mechanism: There are two variants of the discovery mechanism:
- A basic discovery mechanism used to discover LSR neighbors - A basic discovery mechanism used to discover LSR neighbors that
that are directly connected at the link level. are directly connected at the link level.
- An extended discovery mechanism used to locate LSRs that are - An extended discovery mechanism used to locate LSRs that are not
not directly connected at the link level. directly connected at the link level.
2.5.1. Basic Discovery Mechanism 2.4.1. Basic Discovery Mechanism
To engage in LDP Basic Discovery on an interface an LSR periodically To engage in LDP Basic Discovery on an interface an LSR periodically
sends LDP Link Hellos out the interface. LDP Link Hellos are sent as sends LDP Link Hellos out the interface. LDP Link Hellos are sent as
UDP packets addressed to the well known LDP discovery port for the UDP packets addressed to the well-known LDP discovery port for the
"all routers" group multicast address. "all routers" group multicast address.
An LDP Link Hello sent by an LSR carries the LDP Identifier for the An LDP Link Hello sent by an LSR carries the LDP Identifier for the
label space the LSR intends to use for the interface and possibly label space the LSR intends to use for the interface and possibly
additional information. additional information.
Receipt of an LDP Link Hello on an interface identifies a "Hello Receipt of an LDP Link Hello on an interface identifies a "Hello
adjacency" with a potential LDP peer reachable at the link level on adjacency" with a potential LDP peer reachable at the link level on
the interface as well as the label space the peer intends to use for the interface as well as the label space the peer intends to use for
the interface. the interface.
2.5.2. Extended Discovery Mechanism 2.4.2. Extended Discovery Mechanism
LDP sessions between non-directly connected LSRs are supported by LDP LDP sessions between non-directly connected LSRs are supported by LDP
Extended Discovery. Extended Discovery.
To engage in LDP Extended Discovery an LSR periodically sends LDP To engage in LDP Extended Discovery an LSR periodically sends LDP
Targeted Hellos to a specific IP address. LDP Targeted Hellos are Targeted Hellos to a specific IP address. LDP Targeted Hellos are
sent as UDP packets addressed to the well known LDP discovery port at sent as UDP packets addressed to the well-known LDP discovery port at
the specific address. the specific address.
An LDP Targeted Hello sent by an LSR carries the LDP Identifier for An LDP Targeted Hello sent by an LSR carries the LDP Identifier for
the label space the LSR intends to use and possibly additional the label space the LSR intends to use and possibly additional
optional information. optional information.
Extended Discovery differs from Basic Discovery in the following Extended Discovery differs from Basic Discovery in the following
ways: ways:
- A Targeted Hello is sent to a specific IP address rather than - A Targeted Hello is sent to a specific IP address rather than to
to the "all routers" group multicast address for the outgoing the "all routers" group multicast address for the outgoing
interface. interface.
- Unlike Basic Discovery, which is symmetric, Extended Discovery - Unlike Basic Discovery, which is symmetric, Extended Discovery is
is asymmetric. asymmetric.
One LSR initiates Extended Discovery with another targeted One LSR initiates Extended Discovery with another targeted LSR,
LSR, and the targeted LSR decides whether to respond to or and the targeted LSR decides whether to respond to or ignore the
ignore the Targeted Hello. A targeted LSR that chooses to Targeted Hello. A targeted LSR that chooses to respond does so
respond does so by periodically sending Targeted Hellos to the by periodically sending Targeted Hellos to the initiating LSR.
initiating LSR.
Receipt of an LDP Targeted Hello identifies a "Hello adjacency" Receipt of an LDP Targeted Hello identifies a "Hello adjacency" with
with a potential LDP peer reachable at the network level and the a potential LDP peer reachable at the network level and the label
label space the peer intends to use. space the peer intends to use.
2.6. Establishing and Maintaining LDP Sessions 2.5. Establishing and Maintaining LDP Sessions
2.6.1. LDP Session Establishment 2.5.1. LDP Session Establishment
The exchange of LDP Discovery Hellos between two LSRs triggers LDP The exchange of LDP Discovery Hellos between two LSRs triggers LDP
session establishment. Session establishment is a two step process: session establishment. Session establishment is a two step process:
- Transport connection establishment. - Transport connection establishment.
- Session initialization - Session initialization
The following describes establishment of an LDP session between LSRs The following describes establishment of an LDP session between LSRs
LSR1 and LSR2 from LSR1's point of view. It assumes the exchange of LSR1 and LSR2 from LSR1's point of view. It assumes the exchange of
Hellos specifying label space LSR1:a for LSR1 and label space LSR2:b Hellos specifying label space LSR1:a for LSR1 and label space LSR2:b
for LSR2. for LSR2.
2.6.2. Transport Connection Establishment 2.5.2. Transport Connection Establishment
The exchange of Hellos results in a Hello adjacency at LSR1 which The exchange of Hellos results in the creation of a Hello adjacency
binds the link (L) and the label spaces LSR1:a and LSR2:b. at LSR1 that serves to bind the link (L) and the label spaces LSR1:a
and LSR2:b.
1. If LSR1 does not already have an LDP session for the exchange 1. If LSR1 does not already have an LDP session for the exchange
of label spaces LSR1:a and LSR2:b it attempts to open an LDP of label spaces LSR1:a and LSR2:b it attempts to open a TCP
TCP connection for a new session with LSR2. connection for a new LDP session with LSR2.
LSR1 determines the transport addresses to be used at its end LSR1 determines the transport addresses to be used at its end
(A1) and LSR2's end (A2) of the LDP TCP connection. Address (A1) and LSR2's end (A2) of the LDP TCP connection. Address A1
A1 is determined as follows: is determined as follows:
a) If LSR1 uses the Transport Address optional object to a. If LSR1 uses the Transport Address optional object (TLV) in
specify an address, A1 is the address LSR1 advertises via Hello's it sends to LSR2 to advertise an address, A1 is the
the optional object; address LSR1 advertises via the optional object;
b) If LSR1 does not use the Transport Address optional b. If LSR1 does not use the Transport Address optional object,
object, A1 is the source IP address used for Hellos to A1 is the source IP address used in Hellos it sends to
LSR2. LSR2.
Similarly, address A2 is determined as follows: Similarly, address A2 is determined as follows:
a) If LSR2 uses the Transport Address optional object (TLV), a. If LSR2 uses the Transport Address optional object, A2 is
A2 is the address LSR2 advertises via the optional the address LSR2 advertises via the optional object;
object;
b) If LSR2 does not use the Transport Address optional b. If LSR2 does not use the Transport Address optional object,
object, A2 is the source IP address used for Hellos from A2 is the source IP address in Hellos received from LSR2.
LSR2.
2. LSR1 determines whether it will play the active or passive 2. LSR1 determines whether it will play the active or passive role
role in session establishment by comparing addresses A1 and A2 in session establishment by comparing addresses A1 and A2 as
as unsigned integers. If A1 > A2, LSR1 plays the active role; unsigned integers. If A1 > A2, LSR1 plays the active role;
otherwise it is passive. otherwise it is passive.
3. If LSR1 is active, it attempts to establish the LDP TCP con- 3. If LSR1 is active, it attempts to establish the LDP TCP
nection by connecting to the well known LDP port at address connection by connecting to the well-known LDP port at address
A2. If LSR1 is passive, it waits for LSR2 to establish the A2. If LSR1 is passive, it waits for LSR2 to establish the LDP
LDP TCP connection to its well known LDP port. TCP connection to its well-known LDP port.
2.6.3. Session Initialization 2.5.3. Session Initialization
After LSR1 and LSR2 establish a transport connection they negotiate After LSR1 and LSR2 establish a transport connection they negotiate
session parameters by exchanging LDP Initialization messages. The session parameters by exchanging LDP Initialization messages. The
parameters negotiated include LDP protocol version, label distribu- parameters negotiated include LDP protocol version, label
tion method, timer values, VPI/VCI ranges for label controlled ATM, distribution method, timer values, VPI/VCI ranges for label
DLCI ranges for label controlled Frame Relay, etc. controlled ATM, DLCI ranges for label controlled Frame Relay, etc.
Successful negotiation completes establishment of an LDP session Successful negotiation completes establishment of an LDP session
between LSR1 and LSR2 for the advertisement of label spaces LSR1:a between LSR1 and LSR2 for the advertisement of label spaces LSR1:a
and LSR2:b. and LSR2:b.
The following describes the session initialization from LSR1's point The following describes the session initialization from LSR1's point
of view. of view.
1. After the connection is established, if LSR1 is playing the After the connection is established, if LSR1 is playing the active
active role, it initiates negotiation of session parameters by role, it initiates negotiation of session parameters by sending an
sending an Initialization message to LSR2. If LSR1 is Initialization message to LSR2. If LSR1 is passive, it waits for
passive, it waits for LSR2 to initiate the parameter negotia- LSR2 to initiate the parameter negotiation.
tion.
In general when there are multiple links between LSR1 and LSR2 In general when there are multiple links between LSR1 and LSR2 and
and multiple label spaces to be advertised by each, the pas- multiple label spaces to be advertised by each, the passive LSR
sive LSR cannot know which label space to advertise over a cannot know which label space to advertise over a newly established
newly established TCP connection until it receives the first TCP connection until it receives the first LDP PDU on the connection.
LDP PDU on the connection.
By waiting for the Initialization message from its peer the By waiting for the Initialization message from its peer the passive
passive LSR can match the label space to be advertised by the LSR can match the label space to be advertised by the peer (as
peer (as determined from the LDP Identifier in the common determined from the LDP Identifier in the PDU header for the
header for the Initialization message) with a Hello adjacency Initialization message) with a Hello adjacency previously created
previously created when Hellos were exchanged. when Hellos were exchanged.
2. When LSR1 plays the passive role: 1. When LSR1 plays the passive role:
a) If LSR1 receives an Initialization message it attempts to a. If LSR1 receives an Initialization message it attempts to
match the LDP Identifier carried by the message PDU with match the LDP Identifier carried by the message PDU with a
a Hello adjacency. Hello adjacency.
b) If there is a matching Hello adjacency, the adjacency b. If there is a matching Hello adjacency, the adjacency
specifies the local label space for the session. specifies the local label space for the session.
Next LSR1 checks whether the session parameters proposed Next LSR1 checks whether the session parameters proposed in
in the message are acceptable. If they are, LSR1 replies the message are acceptable. If they are, LSR1 replies with
with an Initialization message of its own to propose the an Initialization message of its own to propose the
parameters it wishes to use and a KeepAlive message to parameters it wishes to use and a KeepAlive message to
signal acceptance of LSR2's parameters. If the parame- signal acceptance of LSR2's parameters. If the parameters
ters are not acceptable, LSR1 responds by sending a Nak are not acceptable, LSR1 responds by sending a Session
message and closing the TCP connection. Rejected/Parameters Error Notification message and closing
the TCP connection.
c) If LSR1 cannot find a matching Hello adjacency it sends a c. If LSR1 cannot find a matching Hello adjacency it sends a
Nak message and closes the TCP connection. Session Rejected/No Hello Error Notification message and
closes the TCP connection.
d) If LSR1 receives a KeepAlive in response to its Initiali- d. If LSR1 receives a KeepAlive in response to its
zation message, the session is operational from LSR1's Initialization message, the session is operational from
point of view. LSR1's point of view.
e) If LSR1 receives a Nak message, LSR2 has rejected its e. If LSR1 receives an Error Notification message, LSR2 has
proposed session parameters and LSR1 closes the TCP con- rejected its proposed session and LSR1 closes the TCP
nection. connection.
3. When LSR1 plays the active role: 2. When LSR1 plays the active role:
a) If LSR1 receives a Nak message, LSR2 has rejected its a. If LSR1 receives an Error Notification message, LSR2 has
proposed session parameters and LSR1 closes the TCP con- rejected its proposed session and LSR1 closes the TCP
nection. connection.
b) If LSR1 receives an Initialization message, it checks b. If LSR1 receives an Initialization message, it checks
whether the session parameters are acceptable. If so, it whether the session parameters are acceptable. If so, it
replies with a KeepAlive message. If the session parame- replies with a KeepAlive message. If the session
ters are unacceptable, LSR1 sends a Nak message and parameters are unacceptable, LSR1 sends a Session
closes the connection. Rejected/Parameters Error Notification message and closes
the connection.
c) If LSR1 receives a KeepAlive message, LSR2 has accepted c. If LSR1 receives a KeepAlive message, LSR2 has accepted its
its proposed session parameters. proposed session parameters.
d) When LSR1 has received both an acceptable Initialization d. When LSR1 has received both an acceptable Initialization
message and a KeepAlive message the session is opera- message and a KeepAlive message the session is operational
tional from LSR1's point of view. from LSR1's point of view.
It is possible for a pair of incompatibly configured LSRs that It is possible for a pair of incompatibly configured LSRs that
disagree on session parameters to engage in an endless sequence of disagree on session parameters to engage in an endless sequence
messages as each Naks the other's Initialization messages. An LSR of messages as each NAKs the other's Initialization messages with
must throttle its session setup retry attempts with an exponential Error Notification messages.
backoff in situations where Initialization messages are being
Nak'd. It is also recommended that an LSR detecting such a situa-
tion take action to notify an operator.
2.6.4. Initialization State Machine An LSR must throttle its session setup retry attempts with an
exponential backoff in situations where Initialization messages
are being NAK'd. It is also recommended that an LSR detecting
such a situation take action to notify an operator.
The session establishment setup attempt following a NAK'd
Initialization message must be delayed no less than 15 seconds,
and subsequent delays must grow to a maximum delay of no less
than 2 minutes. The specific session establishment action that
must be delayed is the attempt to open the session transport
connection by the LSR playing the active role.
The throttled sequence of Initialization NAKs is unlikely to
cease until operator intervention reconfigures one of the LSRs.
After such a configuration action there is no further need to
throttle subsequent session establishment attempts (until their
initialization messages are NAK'd).
Due to the asymmetric nature of session establishment,
reconfiguration of the passive LSR will go unnoticed by the
active LSR without some further action. Section "Hello Message"
describes an optional mechanism an LSR can use to signal
potential LDP peers that it has been reconfigured.
2.5.4. Initialization State Machine
It is convenient to describe LDP session negotiation behavior in It is convenient to describe LDP session negotiation behavior in
terms of a state machine. We define the LDP state machine to have terms of a state machine. We define the LDP state machine to have
five possible states and present the behavior as a state transition five possible states and present the behavior as a state transition
table and as a state transition diagram. table and as a state transition diagram.
Session Initialization State Transition Table Session Initialization State Transition Table
STATE EVENT NEW STATE STATE EVENT NEW STATE
NON EXISTENT Session TCP connection established INITIALIZED NON EXISTENT Session TCP connection established INITIALIZED
established established
INITIALIZED Transmit Initialization msg OPENSENT INITIALIZED Transmit Initialization msg OPENSENT
(Active Role)
Receive acceptable OPENREC Receive acceptable OPENREC
Initialization msg Initialization msg
(Passive Role )
Action: Transmit Initialization Action: Transmit Initialization
msg and KeepAlive msg msg and KeepAlive msg
Receive Any other LDP msg NON EXISTENT Receive Any other LDP msg NON EXISTENT
Action: Transmit Nak msg and Action: Transmit Error Notification msg
close transport connection (NAK) and close transport connection
OPENREC Receive KeepAlive msg OPERATIONAL OPENREC Receive KeepAlive msg OPERATIONAL
Receive Any other LDP msg NON EXISTENT Receive Any other LDP msg NON EXISTENT
Action: Transmit Nak msg and Action: Transmit Error Notification msg
close transport connection (NAK) and close transport connection
OPENSENT Receive acceptable OPENREC OPENSENT Receive acceptable OPENREC
Initialization msg Initialization msg
Action: Transmit KeepAlive msg Action: Transmit KeepAlive msg
Receive Any other LDP msg NON EXISTENT Receive Any other LDP msg NON EXISTENT
Action: Transmit Nak msg and Action: Transmit Error Notification msg
close transport connection (NAK) and close transport connection
OPERATIONAL Receive Shutdown msg NON EXISTENT OPERATIONAL Receive Shutdown msg NON EXISTENT
Action: Transmit Shutdown msg and Action: Transmit Shutdown msg and
close transport connection close transport connection
Receive other LDP msgs OPERATIONAL Receive other LDP msgs OPERATIONAL
Timeout NON EXISTENT Timeout NON EXISTENT
Action: Transmit Shutdown msg and Action: Transmit Shutdown msg and
close transport connection close transport connection
skipping to change at page 18, line 19 skipping to change at page 19, line 19
| | | | | | | |
| +------------+ | | +------------+ |
| Session | ^ | | Session | ^ |
| connection | | | | connection | | |
| established | | Rx any LDP msg except | | established | | Rx any LDP msg except |
| V | Init msg or Timeout | | V | Init msg or Timeout |
| +-----------+ | | +-----------+ |
Rx Any other | | | | Rx Any other | | | |
msg or | |INITIALIZED| | msg or | |INITIALIZED| |
Timeout / | +---| |-+ | Timeout / | +---| |-+ |
Tx Nak msg | | +-----------+ | | Tx NAK msg | | +-----------+ | |
| | (Passive Role) | (Active Role) | | | (Passive Role) | (Active Role) |
| | Rx Init msg / | Tx Init msg | | | Rx Acceptble | Tx Init msg |
| | Init msg / | |
| | Tx Init msg | | | | Tx Init msg | |
| | Tx KeepAlive | | | | Tx KeepAlive | |
| V msg V | | V msg V |
| +-------+ +--------+ | | +-------+ +--------+ |
| | | | | | | | | | | |
+---|OPENREC| |OPENSENT|----------------->| +---|OPENREC| |OPENSENT|----------------->|
+---| | | | Rx Any other msg | +---| | | | Rx Any other msg |
| +-------+ +--------+ or Timeout | | +-------+ +--------+ or Timeout |
Rx KeepAlive | ^ | Tx Nak msg | Rx KeepAlive | ^ | Tx NAK msg |
msg | | | | msg | | | |
| | | Rx Init msg / | | | | Rx Acceptable |
| | | Init msg / |
| +----------------+ Tx KeepAlive msg | | +----------------+ Tx KeepAlive msg |
| | | |
| +-----------+ | | +-----------+ |
+----->| | | +----->| | |
|OPERATIONAL| | |OPERATIONAL| |
| |---------------------------->+ | |---------------------------->+
+-----------+ Rx Shutdown msg +-----------+ Rx Shutdown msg
All other | ^ or TIMEOUT / All other | ^ or Timeout /
LDP msgs | | Tx Shutdown msg LDP msgs | | Tx Shutdown msg
| | | |
+---+ +---+
2.6.5. Maintaining Hello Adjacencies 2.5.5. Maintaining Hello Adjacencies
An LDP session with a peer has one or more Hello adjacencies. An LDP session with a peer has one or more Hello adjacencies.
An LDP session has multiple Hello adjacencies when a pair of LSRs are An LDP session has multiple Hello adjacencies when a pair of LSRs is
connected by multiple links that share the same label space; for connected by multiple links that share the same label space; for
example, multiple PPP links between a pair of routers. In this example, multiple PPP links between a pair of routers. In this
situation the Hellos an LSR sends on each such link carries the same situation the Hellos an LSR sends on each such link carry the same
LDP Identifier. LDP Identifier.
LDP includes mechanisms to monitor the necessity of an LDP session LDP includes mechanisms to monitor the necessity of an LDP session
and its Hello adjacencies. and its Hello adjacencies.
LDP uses the regular receipt of LDP Discovery Hellos to indicate a LDP uses the regular receipt of LDP Discovery Hellos to indicate a
peer's intent to use the label space identified by the Hello. An LSR peer's intent to use the label space identified by the Hello. An LSR
maintains a hold timer with each Hello adjacency which it restarts maintains a hold timer with each Hello adjacency 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 con- expires without receipt of a matching Hello from the peer, LDP
cludes that the peer no longer wishes to label switch using that concludes that the peer no longer wishes to label switch using that
label space for the link (or target, in the case of Targeted Hellos) label space for that link (or target, in the case of Targeted Hellos)
in question or that the peer has failed, and it 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 closing the transport
connection. connection.
2.6.6. Maintaining LDP Sessions 2.5.6. Maintaining LDP Sessions
LDP includes mechanisms to monitor the integrity of the session tran- LDP includes mechanisms to monitor the integrity of the LDP session.
sport connection.
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 connection. An LSR main- connection to monitor the integrity of the session. An LSR maintains
tains a keepalive timer for each peer session which it resets when- a KeepAlive timer for each peer session which it resets whenever it
ever it receives an LDP PDU from the session peer. If the keepalive receives an LDP PDU from the session peer. If the KeepAlive timer
timer expires without receipt of an LDP PDU from the peer the LSR expires without receipt of an LDP PDU from the peer the LSR concludes
concludes that the transport connection is bad or that the peer has that the transport connection is bad or that the peer has failed, and
failed, and it terminates the peer session by closing the transport it terminates the LDP session by closing the transport connection.
connection.
An LSR must arrange that its LDP peer sees an LDP PDU from it at After an LDP session has been established, an LSR must arrange that
least every keepalive time period to ensure the peer restarts the its peer receive an LDP PDU from it at least every KeepAlive time
session keepalive timer. The LSR may send any protocol message to period to ensure the peer restarts the session KeepAlive timer. The
meet this requirement. In circumstances where an LSR has no other LSR may send any protocol message to meet this requirement. In
information to communicate to its peer, it sends a KeepAlive message. circumstances where an LSR has no other information to communicate to
its peer, it sends a KeepAlive message.
An LSR may choose to terminate an LDP session with a peer at any An LSR may choose to terminate an LDP session with a peer at any
time. Should it choose to do so, it informs the peer with a Shutdown time. Should it choose to do so, it informs the peer with a Shutdown
message. message.
2.7. Label Distribution and Management 2.6. Label Distribution and Management
2.7.1. Label Distribution Control Mode The MPLS architecture [ARCH] allows an LSR to distribute a FEC label
binding in response to an explicit request from another LSR. This is
known as Downstream On Demand label distribution. It also allows an
LSR to distribute label bindings to LSRs that have not explicitly
requested them. This is known as Downstream Unsolicited label
distribution.
Both of these label distribution techniques may be used in the same
network at the same time. However, for any given LDP session, each
LSR must be aware of the label distribution method used by its peer
in order to avoid situations where one peer using Downstream
Unsolicted label distribution assumes its peer is also. See Section
"Downstream-on-Demand label Advertisement".
2.6.1. Label Distribution Control Mode
The behavior of the initial setup of LSPs is determined by whether The behavior of the initial setup of LSPs is determined by whether
the LSR is operating with independent or ordered LSP control. An LSR the LSR is operating with independent or ordered LSP control. An LSR
may support both types of control as a configurable option. may support both types of control as a configurable option.
2.7.1.1. Independent Label Distribution Control 2.6.1.1. Independent Label Distribution Control
When using independent LSP control, each node may advertise label When using independent LSP control, each LSR may advertise label
mappings to its neighbors at any time it desires. For example, when mappings to its neighbors at any time it desires. For example, when
operating in independent Downstream-on-Demand mode, an LSR may answer operating in independent Downstream-on-Demand mode, an LSR may answer
requests for label mappings immediately, without waiting for a label requests for label mappings immediately, without waiting for a label
mapping from the next hop. When operating in independent Downstream mapping from the next hop. When operating in independent Downstream
allocation mode, an LSR may advertise a label mapping for a FEC to Unsolicited mode, an LSR may advertise a label mapping for a FEC to
its neighbors whenever it is prepared to label-switch that FEC. its neighbors whenever it is prepared to label-switch that FEC.
A consequence of using independent mode is that an upstream label can A consequence of using independent mode is that an upstream label can
be advertised before a downstream label is received. This can result be advertised before a downstream label is received. This can result
in unlabeled packets being sent to the downstream node. in unlabeled packets being sent to the downstream LSR.
2.7.1.2. Ordered Label Distribution Control 2.6.1.2. Ordered Label Distribution Control
When using LSP ordered control, an LSR may initiate the transmission When using LSP ordered control, an LSR may initiate the transmission
of a label mapping only for an FEC for which it has a label mapping of a label mapping only for a FEC for which it has a label mapping
for the FEC next hop, or for which the LSR is the egress. For each for the FEC next hop, or for which the LSR is the egress. For each
FEC for which the LSR is not the egress and no mapping exists, the FEC for which the LSR is not the egress and no mapping exists, the
LSR MUST wait until a label from a downstream LSR for is received LSR MUST wait until a label from a downstream LSR is received before
before mapping the FEC and passing corresponding labels to upstream mapping the FEC and passing corresponding labels to upstream LSRs.
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 attached interfaces). directly 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 boun- 3 FEC elements are reachable by crossing a routing domain
dary, such as another area for OSPF summary net-works, or boundary, such as another area for OSPF summary networks,
another autonomous system for OSPF AS externals and BGP routes or another autonomous system for OSPF AS externals and BGP
[rfc1583] [rfc1771]. routes [rfc1583] [rfc1771].
2.7.2. Label Retention Mode 2.6.2. Label Retention Mode
2.7.2.1. Conservative Label Retention Mode 2.6.2.1. Conservative Label Retention Mode
In Downstream Allocation mode, label mapping advertisements for all In Downstream Unsolicited advertisement mode, label mapping adver-
routes may be received from all peer LSRs. When using conservative tisements for all routes may be received from all peer LSRs. When
label retention, advertised label mappings are only retained if they using conservative label retention, advertised label mappings are
will be used to forward packets (i.e., if they are received from a retained only if they will be used to forward packets (i.e., if they
valid next hop according to routing). If operating in Downstream- are received from a valid next hop according to routing). If operat-
on-Demand mode, label mappings will only be requested of the ing in Downstream-on-Demand mode, an LSR will request label mappings
appropriate next hop LSR according to routing. Since Downstream-on- only from the next hop LSR according to routing. Since Downstream-
Demand mode is primarily used when label conservation is desired on-Demand mode is primarily used when label conservation is desired
(e.g., an ATM switch with limited cross connect space), it is typi- (e.g., an ATM switch with limited cross connect space), it is typi-
cally used with the conservative label retention mode. cally used with the conservative label retention mode.
The main advantage of the conservative mode is that the only the The main advantage of the conservative mode is that only the labels
labels that are required for the forwarding of data are allocated and that are required for the forwarding of data are allocated and main-
maintained. This is particularly important in LSRs where the label tained. This is particularly important in LSRs where the label space
space is inherently limited, such as in an ATM switch. A disadvan- is inherently limited, such as in an ATM switch. A disadvantage of
tage of the conservative mode is that if routing changes the next hop the conservative mode is that if routing changes the next hop for a
for a given destination, a new label must be obtained from the new given destination, a new label must be obtained from the new next hop
next hop before labeled packets can be forwarded. before labeled packets can be forwarded.
2.7.2.2. Liberal Label Retention Mode 2.6.2.2. Liberal Label Retention Mode
In Downstream Allocation mode, label mapping advertisements for all In Downstream Unsolicited advertisement mode, label mapping adver-
routes may be received from all peer LSRs. When using liberal label tisements for all routes may be received from all LDP peers. When
retention, advertised label mappings are retained from all next hops using liberal label retention, every label mappings received from a
regardless of whether they are valid next hops for the advertised peer LSR is retained regardless of whether the LSR is the next hop
mapping. When operating in Downstream-on-Demand mode, label mappings for the advertised mapping. When operating in Downstream-on-Demand
are requested of all peer LSRs. Note, however, that Downstream-on- mode with liberal label retention, an LSR might choose to request
Demand mode is typically associated with ATM switch-based LSRs where label mappings for all known prefixes from all peer LSRs. Note, how-
the conservative approach is recommended. ever, that Downstream-on-Demand mode is typically used by devices
such as ATM switch-based LSRs for which the conservative 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 reac-
tion to routing changes can be quick because labels already exist. tion to routing changes can be quick because labels already exist.
The main disadvantage of the liberal mode is that unneeded label map- The main disadvantage of the liberal mode is that unneeded label map-
pings are distributed and maintained. pings are distributed and maintained.
2.7.3. 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 Down-
stream or Downstream-on-Demand allocation mode. LSRs exchange adver- stream Unsolicited or Downstream-on-Demand advertisement mode. LSRs
tisement modes during initialization. The major difference between exchange advertisement modes during initialization. The major
Downstream and Downstream-on-Demand modes is in which LSR takes difference between Downstream Unsolicited and Downstream-on-Demand
responsibility for initiating mapping requests and mapping advertise- modes is in which LSR takes responsibility for initiating mapping
ments requests and mapping advertisements.
2.8. 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 (as opposed to Downstream-on-Demand) When operating in Downstream Unsolicited mode, the LIB entry for an
more, the LIB entry for an address prefix associates a collection of address prefix associates a collection of (LDP Identifier, label)
(LDP Identifier, label) pairs with the prefix, one such pair for each pairs with the prefix, one such pair for each peer advertising a
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 forward-
ing. To retrieve the label the LSR must be able to map the next hop ing. To retrieve the label the LSR must be able to map the next hop
address for the prefix to an LDP Identifier. 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 With-
draw Address messages. draw 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
2.9. Loop Detection
Each LSR MUST support the configurable loop-detection option. LSRs
perform loop detection via the LSR-path-vector object (TLV) contained
within each Mapping and Query message. Upon receiving such a mes-
sage, the LSR performs loop detection by verifying that its unique
router-id is not already present in the list. If a loop is detected,
the LSR must transmit a NAK message to the sending node, and does
not install the mapping or propagate the message any further. In
addition, if there is an upstream label spliced to the downstream
label for the FEC, the LSR must unsplice the labels. On those mes-
sages in which no loop is detected, the LSR must concatenate itself
to the LSR-path-vector before propagating.
If loop detection is desired in some portion of the network, then it
should be turned on in ALL LSRs within that portion of the network,
else loop detection will not operate properly.
2.10. Loop Prevention via Diffusion
LSR diffusion support is a configurable option, which permits an LSR
to verify that a new routed path is loop free before installing an
LSP on that path. An LSR which supports diffusion does not splice an
upstream label to a new downstream label until it ensures that con-
catenation of the upstream path with the new downstream path will be
loop free.
A LSR which detects a new next hop for an FEC transmits a Query mes-
sage containing its unique router id to each of its upstream peers.
An LSR that receives such a Query message processes the Query as fol-
lows. (The following procedures are described in terms of Ack and
Nak messages. An Ack is a Notification message signalling Success; a
Nak is a Notification message signalling Loop Detected)
o If the downstream LSR not the correct next hop for the given
FEC, the upstream LSR responds with an Ack message, indicating
that the downstream LSR may change to the new path.
o If the downstream LSR is the correct next hop for the given
FEC, the upstream LSR performs loop detection via the LSR-
path-vector.
o If a loop is detected, the upstream LSR responds with a Nak
message that indicates the LSR is to be "pruned, and the LSR
unsplices all connections for that FEC to the downstream node,
thereby pruning itself off of the tree.
o If a loop is not detected, the upstream node concatenates its
unique router-id to the LSR-path-vector, and propagates the
Query message to its upstream peers.
o Each LSR which receives an Ack message from its upstream peer
in response to a query message, in turn forwards the ack-
nowledgement to the downstream LSR which sent the Query mes-
sage.
o If an LSR doesn't receive a Ack Message for a given query
within a "reasonable" period of time, it "unsplices" the
upstream peer that has not responded, and responds with a Nak
message to its downstream peer, indicating the pruning of the
upstream peer.
o An LSR which receives a new Query message for an FEC before it
has received responses from all of its upstream peers for a
previous Query message must concatenate the old and the new
LSR-path-vector within the new query advertisement before pro-
pagating.
o The diffusion computation continues until each upstream path
responds with an acknowledgment. An LSR that does not have any
upstream LDP peers must acknowledge the Query message.
The LSR which began the diffusion may splice its upstream label to
the new downstream label only after receiving an acknowledge mes-
sage from the upstream peer.
As LSR diffusion support is a configurable option, an LSR which
does not support diffusion will never originate a Query message.
However, these LSRs must still recognize and process the Query mes-
sages, as described above.
2.11. Explicitly Routing LSPs
The need for explicit routing (ER) in MPLS has been explored else-
where [ARCH] [FRAME]. At the MPLS WG meeting held during the Wash-
ington IETF there was consensus that LDP should support explicit
routing of LSPs with provision for indication of associated (forward-
ing) priority. This section specifies mechanisms to provide that
support, and provides a means to allow the reservation of 'resources'
for the explicitly routed LSP.
In this document we propose an end to end setup mechanism that could,
in principal, be invoked from either end of the explicitly routed LSP
(ERLSP). However we specify it here only for the case of initiation
by the ingress in the belief that such a mechanism maps naturally to
the setup in the opposite direction. We believe that the, inevit-
able, latency associated with this (end to end) setup mechanism is
tolerable since most of the motivations for ERLSPs, for example
'traffic engineering' imply that the LSPs setup in this manner will
have a long lifetime (at least when compared to those setup in
response to dynamic routing).
We introduce objects and procedures that provide support for:
- Strict and Loose explicit routing
- Specification of class of service
- Reservation of bandwidth
- Route pinning
- ERLSP preemption
Only unidirectional point-to-point ERLSP is specified currently.
The scheme can be easily extended to accommodate multipoint-to-
point ERLSPs. The FEC object (TLV) may be used to determined which
ERLSPs are "merged" to form a multipoint-to- point ERLSP. Alterna-
tively, a multipoint-to-point ERLSP can be setup from the egress by
completely specifying the multipoint- to-point tree. Also, tunnel-
ing ERLSPs within other ERLSPs is for future study.
To setup a ERLSP an LSR (that will be the 'ingress' of the LSP)
generates an explicit request. The explicit request contains an
explicit route object which in turn contains a sequence of explicit
request next hop objects and a pointer to the current entry in that
sequence. The explicit request next hop objects specify the IP
address of the LSRs through which the ERLSP should pass. These LSR
hops specified in the explicit route are referred to as 'peg LSRs'.
An explicit request MUST specify the stream that will be associated
with the ERLSP by inserting the appropriate FEC value in the
request. The FEC value 'opaque tunnel' exists to support ERLSPs
where the intermediate LSRs on the LSP need know nothing about the
traffic flowing on the LSP.
The setup mechanism for ERLSPs employs an end to end protocol.
Individual ERLSPs are uniquely identified by an ERLSPID associated
with them by the LSR that initiates their setup. The ERLSPID is
generated by the ingress LSR of the LSP. The ERLSPID has another
component called Peg ERLSPID which is generated by each peg LSR
when the next peg LSR from itself is loosely routed. This is used
by the intermediate LSRs to identify a loosely routed segment. The
Peg ERLSPID is not used in a segment that is strictly routed.
Requests travel from the 'ingress' of the LSP toward what will be
the 'egress'. Responses indicating the status of the ERLSP request
travel back toward the ingress of the ERLSP. ERLSPID is used in
both Request and Response messages.
The addresses specified in the next hop objects in the explicit
route object should be those of the LSR's IP address or the incom-
ing interfaces on the LSRs through which the LSP should pass. The
ERLSPID, FEC, incoming interface (previous hop) and LDP identifier
of the LSR that generated the message are all stored in an ERLSP
control block. Here's a synopsis of the entire mechanism to
instantiate an ERLSP:
An ingress node originates a ERLSP request message. The message
contains an unique ERLSPID, FEC object, explicit route object,
and an optional object for resource assignment for the ERLSP.
At an intermediate node the 'active' ERNH object is identified
by the pointer in the explicit route object. On message receipt
the pointer always points to the receiving LSR object in the
explicit route message in case of strict routing. If a segment
of ERLSP is loosely routed then pointer always points to the
upstream peg LSR at all the intermediate LSRs in this segment.
The penultimate hop to the downstream peg LSR advances the
pointer to the next ERNH object in the list.
If the ERNH objects subtype indicates 'Strict' then dependent on
the next ERNH IP address the appropriate LDP Identifier for the
LDP session with the next hop and the appropriate output inter-
face are discovered (by using the information learnt from the
address message see Section "LDP Identifiers"). The outgoing
interface (next hop) information is also stored in the ERLSP
control block. In the case of strict ERLSP, the neighbor MUST
be directly adjacent to the current LSR.
If the ERNH object subtype indicates 'Loose' then dependent upon
the next ERNH IP address a next hop is selected as per the FIB
information for the downstream peg LSR. This information is
again maintained in the ERLSP control block. Peg LSRs are
allowed to change the Explicit Route Object if the path to the
next Peg LSR is selected to be 'loose'. This allows the Peg
LSRs to select a specific path to the next Peg LSR. The default
path to the next Peg LSR in case the segment is chosen as
'loose' is determined by the hop-by- hop forwarding path to the
next Peg LSR. However, Peg LSR are allowed only to select a
path downstream to the next Peg LSR, they cannot change paths on
any other segment of the ERLSP.
Bandwidth reservations (if any) are processed. How this hap-
pens, i.e. the precise connection admission procedures is out-
side the scope of the LDP specification. The admission control
must also use the preemption value specified for the LSP in
determining if resources are available for the LSP. If a reser-
vation cannot be accommodated a response indicating that fact is
returned to the previous hop. Note that the resources are only
reserved at this time. The LSRs will commit the bandwidth with
the labels when the response comes back from the egress LSR.
If the ERLSP can be accommodated the pointer in the explicit
request object is incremented to point at the next explicit
request next hop object in case of strict routing and the
request message is sent to the LDP peer discovered as described
above. In case of loose routing, the pointer is incremented
only if the direct next hop is the next downstream peg LSR.
If an LSR finds it impossible to satisfy a Explicit request then
an 'Explicit response' message is created indicating the reason.
The ERLSPID from (failed) request is inserted in the message and
it is sent to the LDP peer identified in the associated entry in
the ERLSP control block after which the ERLSP block is freed.
LSRs receiving Explicit responses indicating failure process
them in a similar manner. They create a new Explicit request
and copy the ERLSPID and Status from the Explicit request they
received into it. They use the ERLSPID to obtain the appropri-
ate ERLSP control block and thus identify the LDP peer toward
which the 'new' Explicit response message should be sent. Hav-
ing done that they free the ERLSP control block.
When an Explicit request reaches the LSR specified in the last
ERNH object in that request and that LSR accedes to the request
it generates an Explicit response indicating successful setup of
the ERLSP. The egress node also includes a label in the
response message. The Explicit response is (reverse path) for-
warded through the LSRs that the original Explicit request
traversed using the mechanism described above (inspection of
ERLSP control block). In this case, of course, the ERLSP con-
trol block is not deleted. An intermediate LSR receiving such a
response message allocates a new label on its incoming interface
and creates a connection between the new and the given label in
the message. The LSR also commits the previously reserved
bandwidth to this connection at the appropriate scheduler(s).
The LSR then forwards the message to its previous hop with the
new label. When the successful response reaches the ingress LSR
the ERLSP is declared in-service.
There is also support for route pinning for loosely routed seg-
ments. When a ERLSP is pinned the loose path is not changed
when `better' paths become available. Once a ERLSP goes in-
service there is protocol support to reassign resources to the
ERLSP if required.
2.12. ERLSP State Machine
The ERLSP control block may contain the following information:
- ERLSPID/Peg ERLSPID
- State
- FEC object
- Flags
o Self is Peg Node
o Pinned path
o Upstream segment (Strict/Loose) type
o downstream segment (Strict/Loose) type
- next peg node
- preemption level
- upstream neighbor (next hop/interface)
- downstream neighbor (next hop/interface)
- BW information (only at peg LSRs with loose downstream
segment)
- Explicit Route Object (only at peg LSRs with loose
downstream segment)
For the purpose of matching message to existing ERLSP control
block, both the ERLSPID and Peg ERLSPID in the message are
matched against the ones in the control block. Its only when
both of them match that the message is considered to be for the
matched control block, otherwise it is treated as a new ERLSP
request. The ingress may use the ERLSPID as the peg ERLSPID.
At the peg nodes, the control block fields ERLSPID and Previous
Peg ERLSDID are compared because Peg ERLSPID contains the self
assigned Peg ERLSPID. Also note that the Request message at
Peg node is only compared for ERLSPID to select a control
block.
The state tables for peg node and non peg nodes are given
separately. Separate state tables are used only for
illustrative purposes. The state engines can be collapsed into
a single state engine. Moreover, a completely strict ERLSP can
be treated as a special case of loosely routed where every
neighbor is a peg LSR with several of the state transitions
optimized.
2.12.1. Loose Segment Peg LSR Transitions:
Peg LSRs in a loosely routed ERLSP segment are those that are expli-
citly listed in the explicit route object as the starting or ending
of a loose segment.
State NULL
Event Action New State
Request Create ERLSP control block; store Response
relevant information from the Awaited
message into the control block;
select a new peg ERLSPID; reserve
BW specified in the message; obtain
next hop (or interface) towards
next peg LSR; propagate message
towards the obtained next hop.
If last node in the explicit route Established
object, allocate an upstream label;
commit BW; originate a Response
message upstream.
If unable to process request for No change
any reason, issue a NAK message to
the sender with appropriate error
code.
Response Send NAK message to the sender. No change
Others Silently ignore event. No change
State RESPONSE_AWAITED
Event Action New State
Response Install downstream label in Established
message; choose an upstream label;
connect upstream to downstream
label; commit BW to the connection;
propagate Response upstream with
upstream label.
If unable to process Response Null
message for any reason then recover
resources; originate a Nak message
upstream; originate a Release
message downstream; delete control
block.
Upstream Release resources; propagate Nak Null
lost downstream; delete control block.
Downstream Reassign a new Peg ERLSPID. Start Retry
lost RETRY timer.
Nak from Reassign a new Peg ERLSPID. RETRY Retry
downstream timer.
If error code in Nak is severe then Null
propagate the Nak upstream; release
resources; delete control block.
Nak from Release resources; propagate Nak Null
upstream downstream; delete control block.
New NH If ERLSP is pinned, ignore event. Retry
Otherwise, send a Nak downstream;
change NH in the control block;
reassign a new Peg ERLSPID. Start
RETRY timer.
Others Silently ignore event. No change
State RETRY
Event Action New State
Retry Originate Request message towards Response
Timer the next hop in the control block. Awaited
New NH If ERLSP is pinned, ignore the No change
event. Otherwise change next hop
information in the control block.
Nak from Release all resources (BW, label, Null
upstream timer); delete control block.
Upstream Release all resources (BW, label, Null
lost timer); delete control block.
Release Release all resources (BW, label, Null
timer); delete control block.
Downstream If there is a new next hop, update No change
lost that in the control block.
Otherwise, delete timer; recover Null
resources; send Nak upstream;
delete control block.
Others Silently ignore event. No change
State RECONNECT_AWAITED
Event Action New State
Request Make appropriate changes in the Established
control block; make label
connection; send a Response message
upstream with upstream label.
If unable to process Request Null
message for any reason then send a
Release message downstream and a
Nak message upstream; release
resources; delete control block.
Reconnect Release resources; send Release Null
Awaited message downstream; delete control
Timer block.
Upstream Ignore event. No change
lost
Downstream Release resources; delete control Null
lost block.
New NH Release resources; delete control Null
block.
Nak from Release resources; delete control Null
downstream block.
Others Silently ignore event. No change
State ESTABLISHED
Event Action New State
Upstream Start RECONNECT_AWAITED timer. Reconnect
lost Awaited
Downstream Reassign a new Peg ERLSPID. Start Retry
lost RETRY timer.
Nak from Reassign a new Peg ERLSPID. Start Retry
downstream RETRY timer.
If error code in Nak is severe then Null
propagate the Nak upstream; release
resources; delete control block.
Nak from Reassign a new Peg ERLSPID. Start Reconnect
upstream RECONNECT_AWAITED timer. Awaited
If error code in Nak is severe, Null 2.8. Loop Detection
then propagate the Nak downstream;
release resources; delete control
block.
New NH If ERLSP is pinned, ignore the Retry Loop detection is a configurable option which provides a mechanism
event. Otherwise, send a Nak for finding looping LSPs and for preventing Label Request messages
downstream; change next hop in from looping in the presence of non-merge capable LSRs.
control block; reassign a new Peg
ERLSPID. Start RETRY timer.
Release Release resources; propagate Null The mechanism makes use of Path Vector and Hop Count TLVs carried by
message downstream; delete control Label Request and Label Mapping messages. It builds on the following
block. basic properties of these TLVs:
Others Silently ignore event. No change - A Path Vector TLV contains a list of the LSRs that its containing
message has traversed. An LSR is identified in a Path Vector
list by its unique LSR Identifier (Id), which is the IP address
component of its LDP Identifier. When an LSR propagates a mes-
sage containing a Path Vector TLV it adds its LSR Id to the Path
Vector list. An LSR that receives a message with a Path Vector
that contains its LSR Id detects that the message has traversed a
loop. LDP supports the notion of a maximum allowable Path Vector
length; an LSR that detects a Path Vector has reached the maximum
length behaves as if the containing message has traversed a loop.
2.12.2. Loose Segment Non-Peg LSR Transitions: - A Hop Count TLV contains a count of the LSRS that the containing
message has traversed. When an LSR propagates a message contain-
ing a Hop Count TLV it increments the count. An LSR that detects
a Hop Count has reached a configured maximum value behaves as if
the containing message has traversed a loop. By convention a
count of 0 is interpreted to mean the hop count is unknown.
Incrementing an unknown hop count value results in an unknown hop
count value (0).
Non-peg LSRs in a loose segment of an ERLSP are the LSRs intermediate The following paragraphs describes LDP loop detection procedures. In
to two peg LSRs and through which the loose segment is routed using these paragraphs, "MUST" means "MUST if configured for loop detec-
the hop-by-hop forwarding path. tion". The paragraphs specify messages that must carry Path Vector
and Hop Count TLVs. Note that the Hop Count TLV and its procedures
are used without the Path Vector TLV in situations when loop detec-
tion is not configured (see [ATM]).
State NULL 2.8.1. Label Request Message
Event Action New State The use of the Path Vector TLV and Hop Count TLV prevent Label
Request messages from looping in environments that include non-merge
capable LSRs.
Request Create ERLSP control block; reserve Response The rules that govern use of the Hop Count TLV in Label Request
BW specified in the message; obtain Awaited messages by LSR R when Loop Detection is enabled are the following:
next hop (or interface) towards
next peg LSR; if penultimate hop to
next peg LSR then increment pointer
in ERNH object; propagate message
towards the obtained next hop
If unable to process request for No change - The Label Request message MUST include a Hop Count TLV.
any reason, issue a Nak message to
the sender with appropriate error
code.
Response Send a Nak message to the sender. No change - 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.
Others Silently ignore event. No change - 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
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
TLV to its next hop along with the Label Request message;
State RESPONSE_AWAITED The rules that govern use of the Path Vector TLV in Label Request
messages by LSR R when Loop Detection is enabled are the following:
Event Action New State - If R is sending the Label Request because it is a FEC ingress, then
if R is non-merge capable, it MUST include a Path Vector TLV of
length 1 containing its own LSR Id.
Response Install downstream label in Established - If R is sending the Label Request as a result of having received a
message; choose an upstream label; Label Request from an upstream LSR, then if the received Label
connect upstream to downstream Request contains a Path Vector TLV or if R is non-merge capable:
label; commit BW to connection;
propagate Response upstream with
upstream label.
If unable to process Response Null R MUST add its own LSR Id to the Path Vector, and MUST pass the
message for any reason then resulting Path Vector to its next hop along with the Label
recovery resources; propagate a Nak Request message. If the Label Request contains no Path Vector
message upstream; originate a TLV, R MUST include a Path Vector TLV of length 1 containing
Release message downstream; delete its own LSR Id.
control block.
Upstream Originate a Nak message downstream; Null Note that if R receives a Label Request message for a particular FEC,
lost delete control block. and R has previously sent a Label Request message for that FEC to its
next hop and has not yet received a reply, and if R intends to merge
the newly received Label Request with the existing outstanding Label
Request, then R does not propagate the Label Request to the next hop.
Downstream Originate a Nak message upstream; Null If R receives a Label Request message from its next hop with a Hop
lost delete control block. Count TLV which exceeds the configured maximum value, or with a Path
Vector TLV containing its own LSR Id or which exceeds the maximum
allowable length, then R detects that the Label Reqeust message has
traveled in a loop.
Nak from Propagate Nak message upstream; Null When R detects a loop, it MUST send a Loop Detected Notification mes-
downstream release reserved BW; delete control sage to the source of the Label Request message and drop the Label
block. Request message.
Nak from Propagate Nak message downstream; Null 2.8.2. Label Mapping Message
upstream release reserved BW; delete control
block;
New NH If ERLSP is pinned, ignore the Null The use of the Path Vector TLV and Hop Count TLV in the Label Mapping
event. Otherwise, send Nak message message provide a mechanism to find and terminate looping LSPs. When
upstream and downstream; release an LSR receives a Label Mapping message from a next hop, the message
reserved BW; delete control block. is propagated upstream as specified below until an a ingress LSR is
reached or a loop is found.
Release Propagate message downstream; Null The rules that govern the use of the Hop Count TLV in Label Mapping
release resources; delete control messages sent by an LSR R when Loop Detection is enabled are the fol-
block. lowing:
Others Silently ignore event. No change - R MUST include a Hop Count TLV.
State ESTABLISHED - If R is the egress, the hop count value MUST be 1.
Event Action New State - If the Label Mapping message is being sent to propagate a Label
Mapping message received from the next hop to an upstream peer, the
hop count value MUST be the result of incrementing the hop count
value received from the next hop.
Upstream Send Nak message downstream; Null - If the Label Mapping message is not being sent to propagate a Label
lost release resources (BW, label); Mapping message, the hop count value MUST be the result of incre-
delete control block. menting R's current knowledge of the hop count to the egress. Note
that the hop count to the egress will be unknown if R has not
received a Label Mapping message from the next hop.
Downstream Send Nak message upstream; release Null Any Label Mapping message MAY contain a Path Vector TLV. The rules
lost resources; delete control block. 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-
ing:
Nak from Release resources; propagate Nak Null - If R is the egress, the Label Mapping message need not include a
downstream message upstream; delete control Path Vector TLV.
block.
Nak from Release resources; propagate Null - If R is sending the Label Mapping message to propagate a Label Map-
upstream message Nak downstream; delete ping message received from the next hop to an upstream peer, then:
control block.
New NH If ERLSP is pinned, ignore the Null o If R is merge capable and if R has not previously sent a Label
event. Otherwise, release Mapping message to the upstream peer, then it MUST include a
resources; originate Nak message Path Vector TLV.
upstream; originate Nak message
downstream; delete control block.
Release Release resources; propagate Null o If the received message contains an unknown hop count, then R
message downstream; delete control MUST include a Path Vector TLV.
block.
Others Silently ignore event. No change o If R has previously sent a Label Mapping message to the
upstream peer, then it MUST include a Path Vector TLV if the
received message reports an LSP hop count increase, a change in
hop count from unknown to known, or a change from known to
unknown.
2.12.2.1. Strict Segment Transitions If the above rules require R include a Path Vector TLV in the Label
Mapping message, R computes it as follows:
A LSR whose upstream and downstream segment of an ERLSP is o If the received Label Mapping message included a Path Vector,
strict has a state transition exactly similar to the non-peg the Path Vector sent upstream MUST be the result of adding R's
LSR (only different being does not handle the case of pinned LSR Id to the received Path Vector.
down option).
2.12.3. ERLSP Timeouts o If the received message had no Path Vector, the Path Vector
sent upstream MUST be a path vector of length 1 containing R's
LSR Id.
The following timeouts are used in the state transition: - If the Label Mapping message is not being sent to propagate a
received message upstream, the Label Mapping message MUST include a
Path Vector of length 1 containing R's LSR Id.
RETRY If R receives a Label Mapping message from its next hop with a Hop
Default value TBD. This timer is set by the peg LSR to ori- Count TLV which exceeds the configured maximum value, or with a Path
ginate a Request message downstream on the elapse of the timer Vector TLV containing its own LSR Id or which exceeds the maximum
when a downstream loose segment is lost. allowable length, then R detects that the corresponding LSP contains
a loop.
RECONNECT When R detects a loop, it MUST stop using the label for forwarding,
Default value TBD. This timer is set by the peg LSR to dein- drop the Label Mapping message. and send a Loop Detected Notification
stall an ERLSP on the elapse of the timer when a upstream message to the source of the Label Mapping message.
loose segment is lost.
2.12.4. ERLSP Error Codes 2.8.3. Discussion
NOTE*NOTE*NOTE*NOTE*NOTE*NOTE: LSRs which are configured for loop detection are NOT expected to
store the path vectors as part of the LSP state.
To be supplied. Note that in a network where only non-merge capable LSRs are present,
Path Vectors are passed downstream from ingress to egress, and are
not passed upstream. Even when merge is supported, Path Vectors need
not be passed upstream along an LSP which is known to reach the
egress. When an LSR experiences a change of next hop, it need pass
Path Vectors upstream only when it cannot tell from the hop count
that the change of next hop does not result in a loop.
This subsection should be moved to Section 3. In the case of ordered label distribution, Label Mapping messages are
propagated from egress toward ingress, naturally creating the Path
Vector along the way. In the case of independent label distribution,
an LSR may originate a Label Mapping message for an FEC before
receiving a Label Mapping message from its downstream peer for that
FEC. In this case, the subsequent Label Mapping message for the FEC
received from the downstream peer is treated as an update to LSP
attributes, and the Label Mapping message must be propagated
upstream. Thus, it is recommended that loop detection be configured
in conjunction with ordered label distribution, to minimize the
number of Label Mapping update messages.
END NOTE * END NOTE * END NOTE: If loop detection is desired in some portion of the network, then it
should be turned on in ALL LSRs within that portion of the network,
else loop detection will not operate properly.
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 pro-
cessing the messages. cessing 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 mes-
sages in an LDP PDU need not be related to one another. For example, sages in an LDP PDU need not be related to one another. For example,
a single PDU could carry a message advertising FEC-label bindings for a single PDU could carry a message advertising FEC-label bindings for
several FECs, another message requesting label bindings for several several FECs, another message requesting label bindings for several
other FECs, and a third notification message signalling some event. other FECs, and a third notification message signaling some event.
3.1. LDP PDUs 3.1. LDP PDUs
Each LDP PDU is a fixed LDP header followed by one or more LDP mes- Each LDP PDU is an LDP header followed by one or more LDP messages.
sages. The fixed LDP header is: The LDP header is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | PDU Length | | Version | PDU Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LDP Identifier | | LDP Identifier |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Res | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version Version
Two octet unsigned integer containing the version number of the Two octet unsigned integer containing the version number of the
protocol. This version of the specification specifies LDP protocol protocol. This version of the specification specifies LDP protocol
version 1. version 1.
PDU Length PDU Length
Two octet integer specifying the total length of this PDU in bytes, Two octet integer specifying the total length of this PDU in
excluding the Version and PDU Length fields. octets, excluding the Version and PDU Length fields.
The maximum allowable PDU Length is negotiable when an LDP session
is initialized. Prior to completion of the negotiation the maximum
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 for which
this PDU applies. The first four octets encode an IP address this PDU applies. The first four octets encode an IP address
assigned to the LSR. This address should be the router-id, also assigned to the LSR. This address should be the router-id, also
used in LSR Path Vector used by loop detection and loop prevention used to identify the LSR in loop detection Path Vectors. The last
procedures. The last two octets identify a label space within the two octets identify a label space within the LSR. For a platform-
LSR. For a platform-wide label space, these should both be zero. wide label space, these should both be zero.
Res Note that there is no alignment requirement for the first octet of an
This field is reserved. It must be set to zero on transmission and LDP PDU.
must be ignored on receipt.
3.2. Type-Length-Value Encoding 3.2. LDP Procedures
LDP defines messages, TLVs and procedures in the following areas:
- Peer discovery;
- Session management;
- Label distribution;
- Notification of errors and advisory information.
The sections that follow describe the message and TLV encodings for
these areas and the procedures that apply to them.
The label distribution procedures are complex and are difficult to
describe fully, coherently and unambiguously as a collection of
separate message and TLV specifications.
Appendix A, "LDP Label Distribution Procedures", describes the label
distribution procedures in terms of label distribution events that
may occur at an LSR and how the LSR must respond. Appendix A is the
specification of LDP label distribution procedures. If a procedure
described elsewhere in this document conflicts with Appendix A,
Appendix A specifies LDP behavior.
3.3. Type-Length-Value Encoding
LDP uses a Type-Length-Value (TLV) encoding scheme to encode much of LDP uses a Type-Length-Value (TLV) encoding scheme to encode much of
LDP message contents. An LDP TLV is encoded as a 2 octet Type field, the information carried in LDP messages.
followed by a 2 octet Length Field followed by a variable length
Value field. An LDP TLV is encoded as a 2 octet field that uses 14 bits to specify
a Type and 2 bits to specify behavior when an LSR doesn't recognize
the Type, followed by a 2 octet Length Field, followed by a variable
length Value field.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | |U|F| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Value | | Value |
~ ~ ~ ~
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear
(=0), a notification must be returned to the message originator and
the entire message must be ignored; if U is set (=1), the unknown
TLV is silently ignored and the rest of the message is processed as
if the unknown TLV did not exist.
F bit
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-
warded. If F is clear (=0), the unknown TLV is not forwarded with
the containing message; if F is set (=1), the unknown TLV is for-
warded with the containing message.
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 the Octet string of Length octets that encodes information to be inter-
interpretation of which is specfied by the Type field. preted as specified by the Type field.
Note that there is no alignment requirement for the first octect of a
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 specifica-
tion does not use the TLV scheme to its full generality. It is not tion does not use the TLV scheme to its full generality. It is not
used where its generality is unnecessary and its use would waste used where its generality is unnecessary and its use would waste
space unnecessarily. These are usually places where the type of a space unnecessarily. These are usually places where the type of a
value to be encoded is known, for example by its position in a mes- value to be encoded is known, for example by its position in a mes-
sage or an enclosing TLV, and the length of the value is fixed or sage 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 is possible to think about TLVs related in this way in terms of While it is possible to think about TLVs related in this way in terms
a TLV type that specifies a TLV class and a TLV subtype that speci- of a TLV type that specifies a TLV class and a TLV subtype that
fies a particular kind of TLV within that class, this specification specifies a particular kind of TLV within that class, this specifica-
does not formalize the notion of a TLV subtype. tion 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 of a contiguous block in the 16-bit TLV type number label TLVs, from of 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 document section that describes each. protocol and the section in this document that describes each.
3.3. Commonly Used TLVs 3.4. TLV Encodings for Commonly Used Parameters
There are several TLV encodings used by more than one LDP message. There are several parameters used by more than one LDP message. The
The encodings for these commonly used TLVs are specified in this sec- TLV encodings for these commonly used parameters are specified in
tion. this section.
3.3.1. FEC TLV 3.4.1. FEC TLV
Labels are bound to Forwarding Equivalence Classes (FECs). An 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC (0x0100) | Length | |U|F| FEC (0x0100) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element 1 | | FEC Element 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element n | | FEC Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
FEC Element 1 to FEC Element n FEC Element 1 to FEC Element n
There are several types of FEC elements; see Section "FEC Types". There are several types of FEC elements; see Section "FECs". The
The FEC element encoding depends on the type of FEC element. Note FEC element encoding depends on the type of FEC element.
that while the representation of the FEC element value is type-
dependent that the value encoding itself is one where standard LDP
TLV encoding is not used.
A FEC Element value is encoded as a 1 octet field that specifies A FEC Element value is encoded as a 1 octet field that specifies
the element type, and a variable length field that is the type- the element type, and a variable length field that is the type-
dependent element value. dependent element value. Note that while the representation of the
FEC element value is type-dependent, the FEC element encoding
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 Prefix value encoding below. Prefix 0x02 See below.
Router Id 0x03 4 octet full IP address. Host Address 0x03 4 octet full IP address; see below.
Flow 0x04 See Flow value encoding below.
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 asso-
ciated with the label within the following label TLV. Must be ciated with the label within the following label TLV. Must be
the only FEC Element in the FEC TLV. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 Assigned Numbers [ref] that encodes the address fam- NUMBERS in [rfc1700] that encodes the address family for the
ily 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.
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.
Flow FEC Element value 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Source Address | | Host Addr (3) | Address Family | Host Addr Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Direction | Reserved | | |
| Host Addr |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Source Address Address Family
Four octet source IPv4 address. Two octet quantity containing a value from ADDRESS FAMILY
NUMBERS in [rfc1700] that encodes the address family for the
Network Destination Address address prefix in the Prefix field.
Four octet destination IPv4 address.
NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
For generality the address encodings here should include an
Address Family field, etc.
END NOTE * END NOTE * END NOTE:
Source Port
Two octet source port.
Destination Port
Two octet destination port.
Protocol
Protocol type.
Direction
One octet indicating the direction of the LSP. Field is set to
1 on Downstream; field is set to 2 on Upstream.
NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
Use of this FEC is not fully specified in this version of the Host Addr Len
protocol Length of the Host address in octets.
END NOTE * END NOTE * END NOTE: Host Addr
An address encoded according to the Address Family field.
3.3.1.1. 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 can-
not decode, it should stop decoding the FEC TLV, abort processing the not decode, it should stop decoding the FEC TLV, abort processing the
message containing the TLV, and send an Ack/Nack message to its LSR message containing the TLV, and send an Notification message to its
peer signalling an error. LDP peer signaling an error.
3.3.2. 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.
3.3.2.1. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Generic Label (0x0200) | Length | |U|F| 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.
3.3.2.2. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ATM Label (0x0201) | Length | |U|F| 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 signifi-
cant. If V-bit is 10, only the VCI is significant. cant. If V-bit is 10, only the VCI is significant.
VPI VPI
skipping to change at page 43, line 6 skipping to change at page 35, line 19
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 signifi-
cant. If V-bit is 10, only the VCI is significant. cant. 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 Connection Identifier. If the VCI is less than 16- bits, it Virtual Channel Identifier. If the VCI is less than 16- bits, it
should be right justified in the field and the preceding bits must should be right justified in the field and the preceding bits must
be set to 0. If Virtual Path switching is indicated in the V-bits be set to 0. If Virtual Path switching is indicated in the V-bits
field, then this field must be ignored by the receiver and set to 0 field, then this field must be ignored by the receiver and set to 0
by the sender. by the sender.
3.3.2.3. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Relay Label (0x0202) | Length | |U|F| 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 43, line 32 skipping to change at page 35, line 45
| 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
values are supported: values are supported:
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 The Data Link Connection Identifier. Refer to [FR] for the label
draft-ietf-mpls-fr-01.txt [FR] for the label values and formats. values and formats.
3.3.3. 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 mes-
sages. sages.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address List (0x0101) | Length | |U|F| 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 Assigned Numbers [ref] that encodes the addresses contained in in [rfc1700] that encodes the addresses contained in the Addresses
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 encod-
ing of the individual addresses depends on the Address Family. ing 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
3.3.4. COS TLV 3.4.4. COS TLV
The COS (Class of Service) TLV may appear as an optional field in The COS (Class of Service) TLV may appear as an optional field in
messages that carry label mappings. Its encoding is: 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
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS (0x0102) | Length | |U|F| COS (0x0102) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| COS Value | | COS Value |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
COS Value
The COS Value may be one of several types, encoded as a 1 octet
type followed by a variable length, type-dependent value. Note
that the encoding of the COS value is not the standard LDP TLV
encoding. Note also that the length of the type-dependent value
can be derived from the length of the COS TLV.
The following COS value encodings are defined by this version of
the protocol:
COS Name Type code Value COS Value
The value field for this TLV is a subject for further study.
IP Prec 0x01 1 octet IP Precedence
If in decoding a COS TLV an LSR encounters a COS type it cannot One possibility is to define a set of CoS values that map to Dif-
decode, it should stop decoding the COS TLV, abort processing the ferentiated Services [DIFFSERV] code points. Other CoS values
message containing the TLV, and send an Ack/Nack message to its LSR could be supported in addition to or in place of the Differentiated
peer signalling an error. Services code points.
3.3.5. Hop Count TLV 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 links require
use of the Hop Count TLV (see [ATM]).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count (0x0103) | Length | |U|F| 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.
3.3.5.1. Hop Count Procedures 3.4.5.1. Hop Count Procedures
During setup of an LSP an LSR may receive a Label Mapping or Label During setup of an LSP an LSR 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. If the LSR then passes a does, it should record the hop count value. If the LSR then pro-
Label Mapping message for the LSP to an upstream peer or a Label pagates the Label Mapping message for the LSP to an upstream peer or
Request to a downstream peer to continue the LSP setup, it must the Label Request message to a downstream peer to continue the LSP
increment the recorded hop count value and include it in a Hop Count setup, it must increment the recorded hop count value and include it
TLV in the message. The first LSR in the LSP should set the hop in a Hop Count TLV in the message. The first LSR in the LSP should
count value to 1. set the hop count value to 1.
If an LSR receives a Label Mapping message containing a Hop Count By convention a value of 0 indicates an unknown hop count. The
TLV, it must check the hop count value to determine whether the hop result of incrementing an unknown hop count is itself an unknown hop
count has wrapped (hop count value = 0). If so, it must reject the count (0).
Label Mapping message in order to prevent a forwarding loop.
3.3.6. Path Vector TLV 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
exceeded its configured maximum allowable value. If so, it must
behave as if the containing message has traversed a loop by sending a
Notification message signaling Loop Detected in reply to the sender
of the message.
The Path Vector TLV is used in messages that implement LDP loop If Loop Detection is configured, the LSR must follow the procedures
detection and prevention. It records the path of LSRs a label adver- specified in Section "Loop Detection".
tisement has traversed to setup an LSP. Its encoding is:
3.4.6. Path Vector TLV
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-
tion mechanism. See Section "Loop Detection". Its use in the Label
Request message records the path of LSRs the request has traversed.
Its use in the Label Mapping message records the path of LSRs a label
advertisement has traversed to setup an LSP.
Its encoding is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector (0x0104) | Length | |U|F| 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-identifiers indicating the path of LSRs the map- A list of router-ids indicating the path of LSRs the message has
ping message has traversed. Each router-id must be the router-id traversed. Each LSR Id is the IP address (router-id) component of
component of the LDP identifier for the corresponding LSR. This the LDP identifier for the corresponding LSR. This ensures it is
ensures it is unique within the LSR network. unique within the LSR network.
3.3.6.1. Path Vector Procedures 3.4.6.1. Path Vector Procedures
During setup of an LSP an LSR may receive a Label Mapping message for The Path Vector TLV is carried in Label Mapping and Label Request
the LSP that contains the Path Vector TLV. If it does, the LSR must messages when loop detection is configured.
pass a Label Mapping message for the LSP to the upstream peer(s) to
continue the LSP setup. This message must include a Path Vector TLV
in the message. The value of the path vector in the Path Vector TLV
must be the received path vector with the LSRs own LSR Id appended to
it.
If an LSR receives a Label Mapping message containing a Path Vector 3.4.6.1.1. Label Request Path Vector
TLV, it must check the path vector value to determine whether the
vector contains its own LSR-id. If so, it must reject the Label Map-
ping message in order to prevent a forwarding loop.
The Path Vector TLV is also used in the Label Query message. See Section "Loop Detection" specifies situations when an LSR must
Sections "Loop Detection" and "Loop Prevention via Diffusion" for include a Path Vector TLV in a Label Request message.
more details.
3.3.7. Status TLV An LSR that receives a Path Vector in a Label Request message must
perform the procedures described in Section "Loop Detection".
If the LSR detects a loop, it must reject the Label Request message.
The LSR must:
1. Transmit a Notification message to the sending LSR signaling
"Loop Detected".
2. Not propagate the Label Reqeust message further.
Note that a Label Request message with Path Vector TLV is forwarded
until:
1. A loop is found,
2. The LSP egress is reached,
3. The maximum Path Vector limit or maximum Hop Count limit is
reached. This is treated as if a loop had been detected.
3.4.6.1.2. Label Mapping Path Vector
Section "Loop Detection" specifies the situations when an LSR must
include a Path Vector TLV in a Label Mapping message.
An LSR that receives a Path Vector in a Label Mapping message must
perform the procedures described in Section "Loop Detection".
If the LSR detects a loop, it must reject the Label Mapping message
in order to prevent a forwarding loop. The LSR must:
1. Transmit a Notification message to the sending LSR signaling
"Loop Detected".
2. Not propagate the message further.
3. Check whether the Label Mapping message is for an existing LSP.
If so, the LSR must unsplice any upstream labels which are
spliced to the downstream label for the FEC.
Note that a Label Mapping message with a Path Vector TLV is forwarded
until:
1. A loop is found,
2. An LSP ingress is reached, or
3. The maximum Path Vector or maximum Hop Count limit is reached.
This is treated as if a loop had been detected.
3.4.7. Status TLV
Notification messages carry Status TLVs to specify events being sig- Notification messages carry Status TLVs to specify events being sig-
nalled. naled.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (0x0300) | Length | |U|F| 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 signalled. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Status Data | |E|F| Status Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
F 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 notifica-
tion. If clear (=0), this is an advisory notification. tion. If clear (=0), this is an advisory notification.
E bit F bit
End-to-end bit. If set (=1), the notification should be for- Forward bit. If set (=1), the notification should be forwarded
warded to the LSR for the next-hop or previous-hop for the LSP, to the LSR for the next-hop or previous-hop for the LSP, if any,
if any, associated with the event being signalled. If clear associated with the event being signaled. If clear (=0), the
(=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.
This specification defines Status Codes (32-bit unsigned integers This specification defines Status Codes (32-bit unsigned integers
with the above encoding). with the above encoding).
A Status Code of 0 signals success. A Status Code of 0 signals success.
Message ID Message ID
If non-zero, 32-bit value that identifies the peer message to which If non-zero, 32-bit value that identifies the peer message to 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
peer message. peer message.
3.4. LDP Messages 3.5. LDP Messages
All LDP messages have the following TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Message Length | |U| Message Type | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| Mandatory Parameters | | Mandatory Parameters |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| Optional Parameters | | Optional Parameters |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown message bit. Upon receipt of an unknown message, if U is
clear (=0), a notification is returned to the message originator;
if U is set (=1), the unknown message is silently ignored.
Message Type Message Type
Identifies the type of message Identifies the type of message
Message Length Message Length
Specifies the length of the message value component (Mandatory plus Specifies the cumulative length in octets of the Message ID, Manda-
Optional Parameters) in octets tory Parameters, and Optional Parameters.
Message Id Message Id
Four octet integer used to identify this message. Used by the 32-bit value used to identify this message. Used by the sending
sending LSR to facilitate identifying notification messages that LSR to facilitate identifying notification messages that may apply
may apply to this message. An LSR sending a notification message to this message. An LSR sending a notification message in response
in response to this message will include this Message Id in the to this message should include this Message Id in the notification
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.
For messages that have required parameters, the required parameters For messages that have required parameters, the required parameters
MUST appear in the order specified by the individual message MUST appear in the order specified by the individual message
specifications in the sections that follow. specifications in the sections that follow.
Optional Parameters Optional Parameters
Variable length set of optional message parameters. Many messages Variable length set of optional message parameters. Many messages
have no optional parameters. have no optional parameters.
For messages that have optional parameters, the optional parameters For messages that have optional parameters, the optional parameters
may appear in any order. may appear in any order.
Note that there is no alignment requirement for the first octet of an
LDP message.
The following message types are defined in this version of LDP: The following message types are defined in this version of LDP:
Message Name Type Section Title Message Name Section Title
Notification "Notification Message"
Hello "Hello Message"
Initialization "Initialization Message"
KeepAlive "KeepAlive Message"
Address "Address Message"
Address Withdraw "Address Withdraw Message"
Label Mapping "Label Mapping Message"
Label Request "Label Request Message"
Label Withdraw "Label Withdraw Message"
Label Release "Label Release Message"
Notification 0x0001 "Notification Message"
Hello 0x0100 "Hello Message"
Initialization 0x0200 "Initialization Message"
KeepAlive 0x0201 "KeepAlive Message"
Address 0x0300 "Address Message"
Address Withdraw 0x0301 "Address Withdraw Message"
Label Mapping 0x0401 "Label Mapping Message"
Label Request 0x0402 "Label Request Message"
Label Withdraw 0x0403 "Label Withdraw Message"
Label Release 0x0404 "Label Release Message"
Label Query 0x0405 "Label Query Message"
Explicit Route Request 0x0500 "Explicit Route Request Message"
Explicit Route Response 0x0501 "Explicit Route Response 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 message are related to one another, for example the Some of the above messages are related to one another, for example
Label Mapping, Label Request, Label Withdraw, and Label Release mes- the Label Mapping, Label Request, Label Withdraw, and Label Release
sages. messages.
While is possible to think about messages related in this way in While is possible to think about messages related in this way in
terms of a message type that specifies a message class and a message terms of a message type that specifies a message class and a message
subtype that specifies a particular kind of message within that subtype that specifies a particular kind of message within that
class, this specification does not formalize the notion of a message class, this specification does not formalize the notion of a message
subtype. subtype.
The specification assigns type values for related messages, such as The specification assigns type values for related messages, such as
the label messages, from of a contiguous block in the 16-bit message the label messages, from of a contiguous block in the 16-bit message
type number space. type number space.
3.4.1. 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 signi-
ficant event. A Notification message signals a fatal error or pro- ficant event. A Notification message signals a fatal error or pro-
vides advisory information regarding an item such as the processing vides advisory information such as the outcome of processing an LDP
of LDP messages or the state of the LDP session. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Notification (0x0001) | Message Length | |U| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) | | Status (TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer used to identify this message. 32-bit value used to identify this message.
Status TLV Status TLV
Indicates the event being signalled. The encoding for the Status Indicates the event being signaled. The encoding for the Status
TLV is specified in Section "Status TLV". TLV is specified in Section "Status TLV".
Optional Parameters Optional Parameters
This variable length field contains 0 or more parameters, each This variable length field contains 0 or more parameters, each
encoded as a TLV. The following Optional Parameters are generic encoded as a TLV. The following Optional Parameters are generic
and may appear in any Notification Message: and may appear in any Notification Message:
Optional Parameter Type Length Value Optional Parameter Type Length Value
Extended Status 0x0301 4 See below Extended Status 0x0301 4 See below
Returned PDU 0x0302 var See below
Returned Message 0x0303 var See below
Other Optional Parameters, specific to the particular event being Other Optional Parameters, specific to the particular event being
signalled 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 addi-
tional information that supplements the status information con- tional information that supplements the status information con-
tained in the Notification Status Code. tained in the Notification Status Code.
3.4.1.1. Notification Message Procedures Returned PDU
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
as much PDU data following the header as appropriate for the
condition being signalled by the Notification message.
Returned Message
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
type and length fields and as much message data following the
type and length fields as appropriate for the condition being
signalled by the Notification message.
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 mes-
sage containing a Status TLV that encodes the information and option- sage containing a Status TLV that encodes the information and option-
ally additional TLVs that provide more information about the event. ally 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 ses-
sion immediately by closing the session TCP connection and discard sion 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 bind-
ings learned via the session. ings learned via the session.
3.4.1.2. Events Signalled by Notification Messages 3.5.1.2. Events Signaled by Notification Messages
It is useful for descriptive purpose to classify events signalled by It is useful for descriptive purpose to classify events signaled by
Notification Messages into the following categories. Notification Messages into the following categories.
3.4.1.2.1. 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 mal-
formed if: formed 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 signalled receiver with the LDP session. This is a fatal error signaled by
by the Bad LDP Identifier Status Code. 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 signalled 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 (< 20) or too long (> TBD). - The PDU Length field is too short (< 20) or too long
This is a fatal error signaled by the Bad PDU Length Status Code. (> maximum PDU length). This is a fatal error signaled by the
Bad PDU Length Status Code. Section "Initialization Message"
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. See Section "Unknown Message Types" - The Message Type is unknown.
for more detail.
If the Message Type is < 0x80000000 (high order bit = 0) it is a If the Message Type is < 0x8000 (high order bit = 0) it is a
fatal error signalled by the Unknown Message Type Status Code. fatal error signaled by the Unknown Message Type Status Code.
If the Message Type is >= 0x8000000 (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 mes-
sage extends beyond the end of the containing LDP PDU. This is a sage extends beyond the end of the containing LDP PDU. This is a
fatal error signalled by the Bad Message Length Status Code. fatal error signaled by the Bad Message Length Status Code.
3.4.1.2.2. Unknown or Malformed TLV 3.5.1.2.2. Unknown or Malformed TLV
Malformed TLVs contained in LDP messages that are part of the LDP Malformed TLVs contained in LDP messages that are part of the LDP
Discovery mechanism are handled by silently discarding the containing Discovery mechanism are handled by silently discarding the containing
message. message.
A TLV contained in an LDP message received on a TCP connection of an A TLV contained in an LDP message received on a TCP connection of an
LDP is malformed if: LDP is malformed if:
- The TLV Length is too large, that is, indicates that the TLV - The TLV Length is too large, that is, indicates that the TLV
extends beyond the end of the containing message. This is a extends beyond the end of the containing message. This is a
fatal error signalled by the Bad TLV Length Status Code. fatal error signaled by the Bad TLV Length Status Code.
- The TLV type is unknown. See Section "Unknown TLV in Known Mes- - The TLV type is unknown.
sage Type" for more detail.
If the TLV type is < 0x80000000 (high order bit 0) it is a fatal If the TLV type is < 0x8000 (high order bit 0) it is a fatal
error signalled by the Unknown TLV Status Code. error signaled by the Unknown TLV Status Code.
If the TLV type is >= 0800000000 (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 han-
dles the TLV but cannot decode the TLV Value. This is dles the TLV but cannot decode the TLV Value. This is inter-
intrepreted as indicative of a bug in either the sending or preted as indicative of a bug in either the sending or receiving
receiving LSR. It is a fatal error signalled by the Malformed LSR. It is a fatal error signaled by the Malformed TLV Value
TLV Value Status Code. Status Code.
3.4.1.2.3. Session Hold Timer Expiration 3.5.1.2.3. Session Hold Timer Expiration
This is a fatal error signalled by the Hold Timer Expired Status This is a fatal error signaled by the Hold Timer Expired Status Code.
Code.
3.4.1.2.4. Unilateral Session Shutdown 3.5.1.2.4. Unilateral Session Shutdown
This is a non-fatal event signalled 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. Note that although this is a provide a reason for the Shutdown. The sending LSR terminates the
"non-fatal" event, the sending LSR terminates the session immediately session immediately after sending the Notification.
after sending the Notification.
3.4.1.2.5. 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 Initial-
ization") may fail if the session parameters received in the Initial- ization") may fail if the session parameters received in the Initial-
ization Message are unacceptable. This is a fatal error. The ization 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 are defined in Sections "Initialization Message Notification and is defined in Sections "Initialization Message".
Status Codes".
3.4.1.2.6. 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 signalled 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 sig-
nal them are described in the sections that describe these messages. nal them are described in the sections that describe these messages.
3.4.1.2.7. Explicitly Routed LSP Setup Events 3.5.1.2.7. Miscellaneous Events
Establishment of an Explicitly Routed LSP may fail for a variety of
reasons. All such failures are considered non-fatal conditions and
they are signalled by the Explicit Response Message.
3.4.1.2.8. Miscellaneous Events
These are events that fall into none of the categories above. There These are events that fall into none of the categories above. There
are no miscellaneous events defined in this version of the protocol. are no miscellaneous events defined in this version of the protocol.
3.4.2. 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 Mechan-
ism; see Section "LDP Discovery". ism; 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hello (0x0100) | Message Length | |U| Hello (0x0100) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Hello Parameters TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer used to identify this message. 32-bit value used to identify this message.
Common Hello Parameters TLV
Specifies parameters common to all Hello messages. The encoding
for the Common Hello Parameters TLV 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| Common Hello Parms(0x0400)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hold Time |T|R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Hold Time,
Hello hold time in seconds. An LSR maintains a record of Hellos
received from potential peers (see Section "Hello Message Pro-
cedures"). Hello Hold Time specifies the time the sending LSR
will maintain its record of Hellos from the receiving LSR without
receipt of another Hello.
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
the minimum of the hold times proposed in their Hellos.
A value of 0 means use the default. There are interface type
specific defaults for Link Hellos as well as a default for Tar-
geted Hellos. A value of 0xfffff means infinite.
T, Targeted Hello
A value of 1 specifies that this Hello is a Targeted Hello. A
value of 0 specifies that this Hello is a Link Hello.
R, Request Send Targeted Hellos
A value of 1 requests the receiver to send periodic Targeted Hel-
los 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
receiving LSR checks whether it has been configured to send Tar-
geted Hellos to the Hello source in response to Hellos with this
request. If not, it ignores the request. If so, it initiates
periodic transmission of Targeted Hellos to the Hello source.
Reserved
This field is reserved. It must be set to zero on transmission
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 version encoded as a TLV. The optional parameters defined by this ver-
of the protocol are sion of the protocol are
Optional Parameter Type Length Value
Targeted Hello 0x0400 0 --
Send Targeted Hello 0x0401 0 --
Transport Address 0x0402 4 See below
Hello Hold Time 0x0403 4 See below
Targeted Hello Optional Parameter Type Length Value
This Hello is a Targeted Hello. Without this optional parameter
the Hello is a Link Hello.
Send Targeted Hello Transport Address 0x0401 4 See below
Requests the receiver to send periodic Targeted Hellos to the Configuration 0x0402 4 See below
source of this Hello. An LSR initiating Extended Discovery uses Sequence Number
this option.
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 is opening the LDP session TCP connection. If this optional TLV
not present the IPv4 source address for the UDP packet carrying is not present the IPv4 source address for the UDP packet car-
the Hello should be used. rying the Hello should be used.
Hello Hold Time Configuration Sequence Number
An LSR maintains a record of Hellos received from potential peers Specifies a 4 octet unsigned configuration sequence number that
(see below) When present, this parameter specifies the time in identifies the configuration state of the sending LSR. Used by
seconds the sending LSR will maintain its record of Hellos from the receiving LSR to detect configuration changes on the
the receiving LSR without receipt of another Hello. When not sending LSR.
present, the sender will use a default hold time. There are
interface type specific defaults for Link Hellos as well a
default for Targeted Hellos.
3.4.2.1. 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
for the Hellos. The LSR maintains a hold timer with the Hello adja- corresponding to the Hellos. The LSR maintains a hold timer with the
cency which it restarts whenever it receives a Hello that matches the Hello adjacency which it restarts whenever it receives a Hello that
Hello adjacency. If the hold timer for a Hello adjacency expires the matches the Hello adjacency. If the hold timer for a Hello adjacency
LSR discards the Hello adjacency: see sections "Maintaining Hello expires the LSR discards the Hello adjacency: see sections "Maintain-
Adjacencies" and "Maintaining LDP Sessions". ing Hello Adjacencies" and "Maintaining LDP Sessions".
A LSR processes a received LDP Hello as follows: We recommend that the interval between Hello transmissions be at most
one third of the Hello hold time.
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 implementa-
tion dependent (see below for example criteria). tion 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 common header for the specified by the LDP identifier in the PDU header for the
Hello, it attempts to establish a session for the label space; Hello, it follows the procedures of Section "LDP Session Estab-
see section "LDP Session Establishment". lishment".
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:
- The LSR has been configured to accept Targeted Hellos, or - The LSR has been configured to accept Targeted Hellos, or
- The LSR has been configured to send Targeted Hellos to - The LSR has been configured to send Targeted Hellos to
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:
Targeted Hello
No special processing required.
Send Targeted Hello
If the Send Targeted Hello option is carried by the Hello,
the LSR checks whether it has been configured to send Tar-
geted Hellos to the Hello source in response to Hellos with
this option. If not, it ignores the option. If so, it
initiates periodic transmission of Targeted Hellos to the
Hello source.
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.
Hello Hold Time Configuration Sequence Number
A pair of LSRs negotiate the hold times they use for Hellos The Configuration Sequence Number optional parameter is used by
from each other. Each LSR proposes a hold time in its Hel- the sending LSR to signal configuration changes to the receiv-
los either explicitly by including the Hold Time optional ing LSR. When a receiving LSR playing the active role in LDP
TLV or implicitly by omitting it. The hold time used by session establishment detects a change in the sending LSR con-
the LSRs is the minimum of the hold times proposed in their figuration, it may clear the session setup backoff delay, if
Hellos. any, associated with the sending LSR (see Section "Session Ini-
tialization").
We recommend that the interval between Hello transmissions be at A sending LSR using this optional parameter is responsible for
most one third of the Hello hold time. maintaining the configuration sequence number it transmits in
Hello messages. Whenever there is a configuration change on
the sending LSR, it increments the configuration sequence
number.
3.4.3. 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 ses-
sion establishment procedure; see Section "LDP Session Establish- sion establishment procedure; see Section "LDP Session Establish-
ment". ment".
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initialization (0x0200) | Message Length | |U| Initialization (0x0200) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Session Parameters TLV | | Common Session Parameters TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer 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 common
to all LDP sessions. to all LDP sessions.
The encoding for the Basic 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Sess Params (0x0500) | Message Length | |U|F| Common Sess Parms (0x0500)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Version | Hold Time | | Protocol Version | Hold Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|D| PVLim | Reserved | 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 pro-
tocol version 1. tocol version 1.
Hold Time Hold 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 Interval. The receiving LSR MUST calculate the value
of the KeepAlive Timer by using the smaller of its proposed of the KeepAlive Timer by using the smaller of its proposed
Hold Time and the Hold Time received in the PDU. The value Hold Time and the Hold Time received in the PDU. The value
chosen for Hold Time indicates the maximum number of seconds chosen for Hold Time indicates the maximum number of seconds
that may elapse between the receipt of successive PDUs from the that may elapse between the receipt of successive PDUs from the
LSR peer. The Keepalive Timer is reset each time a PDU LDP peer. The KeepAlive Timer is reset each time a PDU
arrives. arrives.
A, Label Advertisement Discipline
Indicates the type of Label advertisement. A value of 0 means
Downstream Unsolicited advertisement; a value of 1 means Down-
stream On Demand.
If one LSR proposes Downstream Unsolicted and the other pro-
poses Downstream on Demand, the rules for resolving this
difference is:
- If the session is for a label-controlled ATM link or a
label-controlled Frame Relay link, then Downstream on
Demand must be used.
- Otherwise, Downstream Unsolicted must be used.
If the label advertisement discipline determined in this way is
unacceptable to an LSR, it must send a Session
Rejected/Parameters Advertisement Mode Notification message in
response to the Initialization message and not establish the
session.
D, Loop Detection
Indicates whether loop detection based on path vectors is
enabled. A value of 0 means loop detection is disabled; a
value of 1 means that loop detection is enabled.
PVLim, Path Vector Limit
The configured maximum path vector length. Must be 0 if loop
detection is disabled (D = 0). If the loop detection pro-
cedures would require the LSR to send a path vector that
exceeds this limit, the LSR will behave as if a loop had been
detected for the FEC in question.
When Loop Detection is enabled in a portion of a network, it is
recommended that all LSRs in that portion of the network be
configured with the same path vector limit. Although
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
a possible misconfiguration.
Reserved
This field is reserved. It must be set to zero on transmission
and ignored on receipt.
Max PDU Length
Two octet unsigned integer that proposes the maximum allowable
length for LDP PDUs for the session. A value of 255 or less
specifies the default maximum length of 4096 octets.
The receiving LSR MUST calculate the maximum PDU length for the
session by using the smaller of its and its peer's proposals
for Max PDU Length. The default maximum PDU length applies
before session initialization completes.
If the maximum PDU length determined this way is unacceptable
to an LSR, it must send a Session Rejected/Parameters Max PDU
Length Notification message in response to the Initialization
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 common 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 Pro-
cedures". cedures".
If there is no matching Hello adjacency, the LSR must send a
Session Rejected/No Hello Notification message in response to
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
Label Allocation 0x0501 1 See below ATM Session Parameters 0x0501 var See below
Discipline Frame Relay Session 0x0502 var See below
Loop Detection 0x0502 0 -- Parameters
Merge 0x0503 1 See below
ATM Null Encapsulation 0x0504 0 --
ATM Label Range 0x0600 8 See below
Frame Relay Label Range 0x0601 8 See below
Label Allocation Discipline ATM Session Parameters
Indicates the type of Label allocation. A value of 0 is Used when an LDP session manages label exchange for an ATM link
Downstream allocation, A value of 1 is Downstream On Demand. to specify ATM-specific session parameters.
If this optional parameter is not specfied, Downstream alloca-
tion is used.
Loop Detection 0 1 2 3
If present, indicates that Loop Detection is enabled. If 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
absent, Loop Detection is disabled. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| ATM Sess Parms (0x0501) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M | N |E| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ATM Label Range Component 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ATM Label Range Component N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Merge M, ATM Merge Capabilities
Specifies the merge capabilities of an ATM or Frame Relay Specifies the merge capabilities of an ATM switch. The follow-
switch. The following values are supported in this version of ing values are supported in this version of the specification:
the specification:
Value Meaning Value Meaning
0 Merge not supported 0 Merge not supported
For ATM Merge:
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
For Frame Relay Merge: If the merge capabilities of the LSRs differ, then:
Non-zero Merge supported
ATM Null Encapsulation - Non-merge and VC-merge LSRs may freely interoperate.
If present, specifies that the LSR supports the null
- The interoperability of VP-merge-capable switches with
non-VPN-merge-capable switches is a subject for future
study.
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
LSR domain.
N, Number of label range components
Specifies the number of ATM Label Range Components included in
the TLV.
E, ATM Null Encapsulation
A value of 1 specifies specifies that the LSR supports the null
encapsulation of [rfc1483] for its data VCs on the ATM link encapsulation of [rfc1483] for its data VCs on the ATM link
managed by the LDP session. In this case IP packets are managed by the LDP session. In this case IP packets are car-
carried directly inside AAL5 frames. If absent, the null ried directly inside AAL5 frames. A value of 0 specifies that
encapsulation is not supported. the null encapsulation is not supported.
ATM Label Range Reserved
Used when an LDP session manages label exchange for an ATM link. This field is reserved. It must be set to zero on transmission
The ATM Label Range TLV contains the label range supported by the and ignored on receipt.
transmitting LSR. A receiving LSR MUST calculate the intersection
between the received range and its own supported label range. The One or more ATM Label Range Components
intersection is the range in which the LSR may allocate and accept A list of ATM Label Range Components which together specify the
labels. LSRs may NOT establish an adjacency with neighbors whose Label range supported by the transmitting LSR.
intersection range is NULL.
A receiving LSR MUST calculate the intersection between the
received range and its own supported label range. The inter-
section is the range in which the LSR may allocate and accept
labels. LSRs MUST NOT establish a session with neighbors for
which the intersection of ranges is NULL. In this case, the
LSR must send a Session Rejected/Parameters Label Range Notifi-
cation message in response to the Initialization message and
not establish the session.
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
skipping to change at page 61, line 5 skipping to change at page 56, line 45
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 ori-
ginating switch. If the VCI is less than 16-bits it should ginating switch. If the VCI is less than 16-bits it should
be right justified in this field and preceding bits should be be right justified in this field and preceding bits should be
set to 0. set to 0.
Frame Relay Label Range Frame Relay Session Parameters
Used when an LDP session manages label exchange for a Frame Used when an LDP session manages label exchange for a Frame Relay
Relay link. The Frame Relay Label Range TLV contains the label link to specify Frame Relay-specific session parameters.
range supported by the transmitting LSR. A receiving LSR MUST
calculate the intersection between the received range and its 0 1 2 3
own supported label range. The intersection is the range in 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
which the LSR may allocate and accept labels. LSRs may NOT +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
establish an adjacency with neighbors whose intersection range |U|F| FR Sess Parms (0x0502) | Length |
is NULL. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M | N | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Relay Label Range Component 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Relay Label Range Component N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M, Frame Relay Merge Capabilities
Specifies the merge capabilities of a Frame Relay switch. The
following values are supported in this version of the specifi-
cation:
Value Meaning
0 Merge not supported
1 Merge supported
Non-merge and merge Frame Relay LSRs may freely interoperate.
N, Number of label range components
Specifies the number of Frame Relay Label Range Components
included in the TLV.
Reserved
This field is reserved. It must be set to zero on transmission
and ignored on receipt.
One or more Frame Relay Label Range Components
A list of Frame Relay Label Range Components which together
specify the Label range supported by the transmitting LSR.
A receiving LSR MUST calculate the intersection between the
received range and its own supported label range. The inter-
section is the range in which the LSR may allocate and accept
labels. LSRs MUST NOT establish a session with neighbors for
which the intersection of ranges is NULL. In this case, the
LSR must send a Session Rejected/Parameters Label Range Notifi-
cation message in response to the Initialization message and
not establish the session.
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
This field is reserved. It must be set to zero on transmis-
sion 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
3.4.3.1. Initialization Message Procedures Minimum DLCI
This 23-bit vield specifies the lower bound of a block of
Data Link Connection Identifiers (DLCIs) that is supported on
the originating switch. The DLCI should be right justified
in this field and unused bits should be set to 0.
Maximum DLCI
This 23-bit vield specifies the upper bound of a block of
Data Link Connection Identifiers (DLCIs) that is supported on
the originating switch. The DLCI should be right justified
in this field and unused bits should be set to 0.
Note that there is no Generic Session Parameters TLV for sessions
which advertise Generic Labels.
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.
3.4.4. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| KeepAlive (0x0201) | Message Length | |U| KeepAlive (0x0201) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer 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.
3.4.4.1. KeepAlive Message Procedures 3.5.4.1. KeepAlive Message Procedures
The Hold Timer mechanism described in Section "Maintaining LDP Ses- The Hold Timer mechanism described in Section "Maintaining LDP Ses-
sions" resets a seesion hold timer every time an LDP PDU is received. sions" resets a session hold timer every time an LDP PDU is received.
The KeepAlive Message is provided to allow reset of the Hold Timer in The KeepAlive Message is provided to allow reset of the Hold Timer in
circumstances where an LSR has no other information to communicate to circumstances where an LSR has no other information to communicate to
an LDP peer. an LDP peer.
An LSR must arrange that its peer sees 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. That message may be any other from the least every Hold Time period. Any LDP protocol message will do but,
protocol or, in circumstances where there is no need to send one of in circumstances where no other LDP protocol messages have been sent
them, it must be KeepAlive Message. within the period, a KeepAlive message must be sent.
3.4.5. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address (0x0300) | Message Length | |U| Address (0x0300) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Address List TLV | | Address List TLV |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer 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.
3.4.5.1. 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 Identif-
iers and next hop addresses; see section "LDP Identifiers and Next iers and next hop addresses; see Section "LDP Identifiers and Next
Hop Addresses". 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 Map-
ping or Label Request messages and LSR should advertise its interface ping or Label Request messages an LSR should advertise its interface
addresses with one or more Address messages. 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 adver-
tise the new address with an Address message. tise 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".
3.4.6. 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 Message to an LDP peer to withdraw previ-
ously advertised interface addresses. ously 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Withdraw (0x0301) | Message Length | |U Address Withdraw (0x0301) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Address List TLV | | Address List TLV |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer 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 mes-
sage. sage.
3.4.6.1. Address Withdraw Message Procedures 3.5.6.1. Address Withdraw Message Procedures
See Section "Address Message Procedures" See Section "Address Message Procedures"
3.4.7. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Mapping (0x0400) | Message Length | |U| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Label Mapping TLV 1 | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | Label TLV |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Label Mapping TLV n | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer used to identify this message. 32-bit value used to identify this message.
FEC-Label Mapping TLV FEC TLV
Each specifies a binding between an FEC and a label. A FEC-Label Specifies the FEC component of the FEC-Label mapping being adver-
Mapping TLV is a nested TLV that contains a FEC TLV, a Label TLV, tised. See Section "FEC TLV" for encoding.
an optional COS TLF, an optional Hop Count TLV, and an optional
Path Vector TLV:
0 1 2 3 Label TLV
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 Specifies the Label component of the FEC-Label mapping. See Sec-
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ tion "Label TLV" for encoding.
| FEC-label Mapping (0x0700) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The encodings for the FEC, Label, COS, Hop Count, and Path Vector Optional Parameters
TLVs can be found in Section "Commonly Used TLVs". This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are:
NOTE*NOTE*NOTE*NOTE*NOTE*NOTE: Optional Parameter Length Value
Need to add multipath possibility to above by allowing multiple Label Request 4 See below
label TLVs to the FEC-label Mapping TLV. This will be done with Message Id
the addition: COS TLV 1 See below
Hop Count TLV 1 See below
Path Vector TLV variable See below
Label TLV2 (optional) The encodings for the COS, Hop Count, and Path Vector TLVs can be
... found in Section "TLV Encodings for Commonly Used Parameters".
Label TLVn (optional)
with discussion. Label Request Message Id
If this Label Mapping message is a response to a Label Request
message that carried the Return Message Id optional parameter
(see Section "Label Request Message") the Label Mapping message
must include the Request Message Id optional parameter. The
value of this optional parameter is the Message Id of the
corresponding Label Request Message.
END NOTE * END NOTE * END NOTE: 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.
Optional Parameters Hop Count
No optional parameters are defined for the Label Mapping message. Specifies the running total of the number of LSR hops along the
LSP being setup by the Label Message. Section "Hop Count Pro-
cedures" describes how to handle this TLV.
3.4.7.1. Label Mapping Message Procedures Path Vector
Specifies the LSRs along the LSP being setup by the Label Mes-
sage. Section "Path Vector Procedures" describes how to handle
this TLV.
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 its LDP peers. If an LSR distributes a mapping for a for a FEC to an LDP peer. If an LSR distributes a mapping for a FEC
FEC to multiple LDP peers, it is a local matter whether it maps a to multiple LDP peers, it is a local matter whether it maps a single
single label to the FEC, and distributes that mapping to all its label to the FEC, and distributes that mapping to all its peers, or
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 always responsible for the consistency of the label map- An LSR is responsible for the consistency of the label map- pings it
pings it has distributed, and that its peers have these mappings. has distributed, and that its peers have these mappings.
3.4.7.1.1. Independent Control Mapping See Appendx A "LDP Label Distribution Procedures" for more details.
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 an LSR to peers 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 allocation. label advertisement mode is Downstream Unsolicited advertise-
ment.
2. The LSR receives a Request message from an upstream peer for an 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 an FEC changes to another LDP peer, and loop 3. The next hop for a FEC changes to another LDP peer, and loop
detection is configured. detection is configured.
4. The attributes of a mapping change. 4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND 5. The receipt of a mapping from the downstream next hop AND
a) no upstream mapping has been created OR a) no upstream mapping has been created OR
b) loop detection is configured OR b) loop detection is configured OR
c) the attributes of the mapping have changed. c) the attributes of the mapping have changed.
3.4.7.1.2. Ordered Control Mapping 3.5.7.1.2. Ordered Control Mapping
If an LSR is doing ordered control, a Mapping message is transmitted If an LSR is doing ordered control, a Mapping message is transmitted
by downstream LSRs upon any of the following conditions: by downstream LSRs upon any of the following conditions:
1. The LSR recognizes a new FEC via the forwarding table, and is 1. The LSR recognizes a new FEC via the forwarding table, and is
the egress for that FEC. the egress for that FEC.
2. The LSR receives a Request message from an upstream peer for an 2. The LSR receives a Request message from an upstream peer for a
FEC present in the LSR's forwarding table, and the LSR is the FEC present in the LSR's forwarding table, and the LSR is the
egress for that FEC OR has a downstream mapping for that FEC. egress for that FEC OR has a downstream mapping for that FEC.
3. The next hop for an FEC changes to another LDP peer, and loop 3. The next hop for a FEC changes to another LDP peer, and loop
detection is configured. detection is configured.
4. The attributes of a mapping change. 4. The attributes of a mapping change.
5. The receipt of a mapping from the downstream next hop AND 5. The receipt of a mapping from the downstream next hop AND
a) no upstream mapping has been created OR a) no upstream mapping has been created OR
b) loop detection is configured OR b) loop detection is configured OR
c) the attributes of the mapping have changed. c) the attributes of the mapping have changed.
3.4.7.1.3. 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 map-
pings when operating in Downstream-on-Demand mode. However, unless pings when operating in Downstream-on-Demand mode. However, unless
some rules are followed, it is possible for neighboring LSRs with some rules are followed, it is possible for neighboring LSRs with
different advertisement modes to get into a livelock situation where different advertisement modes to get into a livelock situation where
everything is functioning properly, but no labels are distributed. everything is functioning properly, but no labels are distributed.
For example, consider two LSRs Ru and Rd where Ru is the upstream LSR For example, consider two LSRs Ru and Rd where Ru is the upstream LSR
and Rd is the downstream LSR for a particular FEC. In this example, and Rd is the downstream LSR for a particular FEC. In this example,
Ru is using Downstream allocation mode and Rd is using Downstream- Ru is using Downstream Unsolicited advertisement mode and Rd is using
on-Demand mode. In this case, Rd may assume that Ru will request a Downstream-on-Demand mode. In this case, Rd may assume that Ru will
label mapping when it wants one and Ru may assume that Rd will adver- request a label mapping when it wants one and Ru may assume that Rd
tise a label if it wants Ru to use one. If Rd and Ru operate as sug- will advertise a label if it wants Ru to use one. If Rd and Ru
gested, no labels will be distributed and packets must be routed at operate as suggested, no labels will be distributed from Rd to Ru.
layer-3.
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.
However, if all interfaces on an LSR are configured to operate in
Downstream- on-Demand mode the LSR can wait to issue a request until
a corresponding request has been sent from an upstream LSR.
3.4.7.1.4. Downstream Allocation 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.
3.4.8. 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 one or more specific FECs. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Request (0x0401) | Message Length | |U| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Request TLV 1 | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Request TLV n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer used to identify this message. 32-bit value used to identify this message.
FEC-Request TLV FEC TLV
Each specifies an FEC for which a label mapping is requested. A The FEC for which a label is being requested. See Section "FEC
FEC-Request TLV is a nested TLV that contains a FEC TLV, an TLV" for encoding.
optional COS TLV, and an optional Hop Count TLV.
0 1 2 3 Optional Parameters
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 This variable length field contains 0 or more parameters, each
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ encoded as a TLV. The optional parameters are:
| FEC-Request (0x0701) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The encodings for the FEC, COS, and Hop Count TLVs are specified in Optional Parameter Length Value
Section "Commonly Used TLVs".
Optional Parameters Return Message Id 0 See below
No optional parameters are defined for the Label Request message. COS TLV 1 See below
Hop Count TLV 1 See below
Path Vector TLV variable See below
3.4.8.1. Label Request Message Procedures The encodings for the COS, Hop Count, and Path Vector TLVs can be
found 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
Specifies the running total of the number of LSR hops along the
LSP being setup by the Label Request Message. Section "Hop
Count Procedures" describes how to handle this TLV.
Path Vector
Specifies the LSRs along the LSR being setup by the Label
Request Message. Section "Path Vector Procedures" describes
how to handle this TLV.
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 an FEC. that the downstream LSR assign and advertise a label for a FEC.
An LSR transmits a Request message under any of the following condi- An LSR may transmit a Request message under any of the following con-
tions: ditions:
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 Operational LDP peer, and the LSR doesn't next hop is an LDP peer, and the LSR doesn't already have a
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.
If a request cannot be satisfied by the downstream LSR, the request- 3. The LSR receives a Label Request for a FEC from an upstream LDP
ing LSR may optionally choose to request again at a later time, or, peer, the FEC next hop is an LDP peer, and the LSR doesn't
if the downstream LSR is configured for Downstream Allo- cation, the already have a mapping from the next hop.
requesting LSR may wait for the mapping, assuming that the downstream
LSR will provide the mapping automatically when it is available.
NOTE*NOTE*NOTE*NOTE*NOTE*NOTE: The receiving LSR should respond to a Label Request message with a
Label Mapping for the requested label or with a Notification message
indicating why it cannot satisfy the request.
In the case where the downstream LSR is doing DoD, how does the This version of the protocol defines the following Status Codes for
requesting LSR decide when to make its request? the Notification message that signals a request cannot be satisfied:
TDP addresses this issue by having a "now I have label resources" No Route
message which it sends to downwstream peers whose requests it has The FEC for which a label was requested is for a Prefix FEC Ele-
denied. This serves as a signal to them to re-issue their ment, and the LSR does not have a route for that prefix.
requests. LDP should probably have this. Without such a signal,
the denied requester has no recourse but to periodically retry.
END NOTE * END NOTE * END NOTE: No Label Resources
The LSR cannot provide a label because of resource limitations.
When resources become available the LSR must notify the request-
ing LSR by sending a Notification message with the Label
Resources Available Status Code.
3.4.9. Label Withdraw Message An LSR that receives a No Label Resources response to a Label
Request message must not issue further Label Request messages
until it receives a Notification message with the Label Resources
Available Status code.
Loop Detected
The LSR has detected a looping Label Requst message.
See Appendx A "LDP Label Distribution Procedures" for more details.
3.5.9. 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 map-
pings the LSR had previously advertised. This breaks the mapping pings 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Withdraw (0x0402) | Message Length | |U| Label Withdraw (0x0402) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Withdraw-Release TLV 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Withdraw-Release TLV n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
Four octet integer used to identify this message.
FEC-Withdraw-Release TLV
Each TLV specifies a FEC-label mapping being withdrawn. A FEC-
Withdraw-Release TLV is a nested TLV that contains a FEC TLV and an
optional label TLV.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Withdraw-Release (0x0702) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) | | Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The encodings for the FEC and Label TLVs are specified in Section Message Id
"Commonly Used TLVs". 32-bit value used to identify this message.
NOTE*NOTE*NOTE*NOTE*NOTE*NOTE: FEC TLV
Identifies the FEC for which the FEC-label mapping is being with-
drawn.
Need to add multipath possibility to above by allowing multiple Optional Parameters
label TLVs to the FEC-label Mapping TLV. This will be done with This variable length field contains 0 or more parameters, each
the addition: encoded as a TLV. The optional parameters are:
Label TLV2 (optional) Optional Parameter Length Value
...
Label TLVn (optional)
with discussion. Label TLV variable See below
END NOTE * END NOTE * END NOTE: The encoding for Label TLVs are found in Section "Label TLVs".
Optional Parameters Label
No optional parameters are defined for the Label Withdraw message. If present, specifies the label being withdrawn (see procedures
below).
3.4.9.1. Label Withdraw Message Procedures 3.5.9.1. Label Withdraw Message Procedures
An LSR transmits a Withdraw message under the following condition: An LSR transmits a Label Withdraw message under the following condi-
tions:
1. The LSR no longer recognizes a previously known FEC. 1. The LSR no longer recognizes a previously known FEC.
2. Optionally, the LSR has unspliced an upstream label from the 2. The LSR has decided unilaterally (e.g., via configuration) to
downstream label. no longer label switch a FEC (or FECs) with the label mapping
being withdrawn.
The FEC in the FEC-Withdraw-Release TLV is a FEC for which labels are The FEC TLV specifies the FEC for which labels are to be withdrawn.
to be withdrawn. If no label TLV follows the FEC, all labels associ- If no Label TLV follows the FEC, all labels associated with the FEC
ated with the FEC are to be withdrawn, else only the labels specified are to be withdrawn; otherwise only the label specified in the
in the following Label TLV are to be withdrawn. optional Label TLV is to be withdrawn.
3.4.10. Label Release Message The FEC TLV may contain the Wildcard FEC Element; if so, it may con-
tain no other FEC Elements. In this case, if the Label Withdraw mes-
sage contains an optional Label TLV, then the label is to be with-
drawn from all FECs to which it is bound. If there is not an
optional Label TLV in the Label Withdraw message, then the sending
LSR is withdrawing all label mappings previously advertised to the
receiving LSR.
See Appendx A "LDP Label Distribution Procedures" for more details.
3.5.10. 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 previ-
ously requested of and/or advertised by the peer. ously 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Release (0x0403) | Message Length | |U| Label Release (0x0403) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Withdraw-Release TLV 1 | | FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-Withdraw-Release TLV n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters | | Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id Message Id
Four octet integer used to identify this message. 32-bit value used to identify this message.
FEC-Withdraw-Release TLVs
Each TLV specifies a FEC-label mapping being released. The encod-
ing for the FEC-Withdraw-Release TLV is specified in Section "With-
draw Message".
NOTE*NOTE*NOTE*NOTE*NOTE*NOTE:
Need to add multipath possibility to above by allowing multiple FEC TLV
label TLVs to the FEC-label Mapping TLV. This will be done with Identifies the FEC for which the FEC-label mapping is being
the addition: released.
Label TLV2 (optional) Optional Parameters
... This variable length field contains 0 or more parameters, each
Label TLVn (optional) encoded as a TLV. The optional parameters are:
with discussion. Optional Parameter Length Value
Label TLV variable See below
END NOTE * END NOTE * END NOTE: The encodings for Label TLVs are found in Section "Label TLVs".
Optional Parameters Label
No optional parameters are defined for the Label Release message. If present, the label being released (see procedures below).
3.4.10.1. Label Release Message Procedures 3.5.10.1. Label Release Message Procedures
An LSR transmits a Release message to a peer when it is no longer An LSR transmits a Label Release message to a peer when it is no
needs a label previously received from or requested of that peer. longer needs a label previously received from or requested of that
peer.
An LSR transmits a Release message under any of the following condi- An LSR must transmit a Label Release message under any of the follow-
tions: ing 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 determines that a previously received label is no 2. The LSR receives a label mapping from an LSR which is not the
longer valid, as the downstream LSR from which it was received next hop for the FEC, and the LSR is configured for conserva-
is no longer the next hop for the FEC, and the LSR is config- tive operation.
ured for conservative operation.
3. The LSR has received a Withdraw message for a previously 3. The LSR has received a Label Withdraw message for a previously
received label. 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 mes-
sage will never be transmitted in the case of conditions (1) and (2) sage will never be transmitted in the case of conditions (1) and (2)
as specified above. In this case, the upstream LSR keeps each unused as specified above. In this case, the upstream LSR keeps each unused
label, so that it can immediately be used later if the downstream label, so that it can immediately be used later if the downstream
peer becomes the next hop for the FEC. peer becomes the next hop for the FEC.
The FEC in the FEC-Withdraw-Release TLV is a FEC for which labels are The FEC TLV specifies the FEC for which labels are to be released.
to be released. If no label TLV follows the FEC TLV, all labels If no Label TLV follows the FEC, all labels associated with the FEC
associated with the FEC are to be released, else only the labels are to be released; otherwise only the label specified in the
specified in the following Label TLV are to be released. optional Label TLV is to be released.
3.4.11. Label Query Message The FEC TLV may contain the Wildcard FEC Element; if so, it may con-
tain no other FEC Elements. In this case, if the Label Release mes-
sage contains an optional Label TLV, then the label is to be released
for all FECs to which it is bound. If there is not an optional Label
TLV in the Label Release message, then the sending LSR is releasing
all label mappings previously learned from the receiving LSR.
An LSR sends a Label Query message to an LDP peer when performing the See Appendx A "LDP Label Distribution Procedures" for more details.
loop prevention diffusion algorithm on an FEC.
The encoding for the Label Query Message is: 3.6. Messages and TLVs for Extensibility
0 1 2 3 Support for LDP extensibility includes the rules for the U and F bits
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 that specify how an LSR should handle unknown TLVs and messages.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Query (0x0405) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id This section specifies TLVs and messages for vendor-private and
Four octet integer used to identify this message. experimental use.
The encodings for the FEC and Path Vector TLVs can be found in Sec- 3.6.1. LDP Vendor-private Extensions
tion "Commonly Used TLVs".
Optional Parameters Vendor-private TLVs and messages are used to convey vendor-private
No optional parameters are defined for the Label Query message. information between LSRs.
3.4.11.1. Label Query Message Procecures 3.6.1.1. LDP Vendor-private TLVs
See Section "Loop Prevention via Diffusion" for general procedures The Type range 0x2F00 through 0x2FFF is reserved for vendor-private
for handling the Query Message. TLVs.
3.4.12. Explicit Route Request Message 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER Request (0x0500) | Message Length | |U|F| Type (0x2F00-0x2FFF) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-ER TLV 1 | | Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Data.... |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-ER TLV n | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Id
Four octet integer used to identify this message.
FEC-ER TLV
Each specifies a binding between an FEC and a label. A FEC-ER TLV
is a nested TLV that contains a FEC TLV, a Label TLV, an explicit-
route identifier (ERLSPID) TLV, the explict-route TLV, an optional
COS TLF, and an optional Bandwith Reservation TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC-ER TLV (0x0703) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ERLSPID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Explicit Route TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Reservation TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The encodings for the FEC and COS TLVs can be found in Section
"Commonly Used TLVs".
ERLSPID TLV
The globally unique value that identifies the explicit route.
The encoding for the ERLSPID 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ERLSPID (0x0801) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Explicit Identifier |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Peg Explicit Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Explicit Identifier
A 6-octet globally unique value that identifies the explicit
route LSP. It is generated by the LSR that creates the Expli-
cit Request message. The first four octets is the LSR IP
Address. The last two octets contain a `Local identifier'
value. It is incumbent on an LSR that originates an Explicit
Request message to choose an unused value for the Local Iden-
tifier.
Peg Explicit Identifier
A 6-octet globally unique value that identifies a loose segment
of an explicit route LSP. It is generated by the upstream peg
LSR that creates the loose segment. The first four octets is
the LSR IP Address. The last two octets contain a 'Local iden-
tifier' value. It is incumbent on a peg LSR that creates a
loose segment to choose an unused value for the Local Identif-
ier every time the segment is reestablished. When a segment is
strictly routed this field is set to zero by the sender and
ignored by the receiver.
Explicit Route TLV
The sequence of ER Next Hop (ERNH) TLVs and a pointer to the one
that should be processed by the LSR that receives this ER TLV.
The encoding for the Explicit Route 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Explicit Route TLV (0x0800) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next ERNH TLV Pointer | Reserved |P|Preempt|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ERNH TLV (Variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next ERNH TLV Pointer
This 16 bit unsigned integer points to the offset in octets of
the next ERNH TLV to be processed. The first octet after the
two reserved octets that follow this pointer is defined to have
an offset value of zero. For example an ERNH TLV Pointer value
of zero would point to the first ERNH TLV in the sequence of
ERNH Objects.
P bit
when set indicates that the loosely routed segments must remain
pinned-down. ERLSP must be rerouted only when adjacency is
lost along the segment. When not set indicates loose segment
is not pinned down and must be changed to match the underlying
hop-by-hop path.
Preempt
A 16 level preemption is provided to facilitate placement of
ERLSP when resources aren't available. Each LSR maintains this
value in the ERLSP control block. A higher preemption value
can preempt LSPs with lower value.
Reserved
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
ERNH TLV
This TLV contains the four octet IP address of an LSR through
which the Explicit Route LSP is to pass and an (optional)
reservation (RES) TLV to be processed by that LSR.
The strict TLV indicates that the ER LSP setup must be routed
directly via the LSR indicated in the ERNH object; i.e. that
that LSR must be the next hop in the Explicit Route LSP's path.
The loose TLV indicates that the LSP may be routed in any way;
i.e. via other unspecified LSRs, so long as it (eventually)
reaches the LSR specified in the ERNH object. This TLV may be
followed by the optional Reservation TLV.
The ERNH encodings are: U bit
0 1 2 3 Unknown TLV bit. Upon receipt of an unknown TLV, if U is clear
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), a notification must be returned to the message originator and
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ the entire message must be ignored; if U is set (=1), the unknown
| ER Strict TLV (0x0802) | Length | TLV is silently ignored and the rest of the message is processed as
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ if the unknown TLV did not exist.
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 The determination as to whether a vendor-private message is under-
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 stood is based on the Type and the mandatory Vendor ID field.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER Loose TLV (0x0803) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Ipv4 Address F bit
The IP address of the next LSR in the Explicit Route LSP. 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-
warded. If F is clear (=0), the unknown TLV is not forwarded with
the containing message; if F is set (=1), the unknown TLV is for-
warded with the containing message.
Bandwidth Reservation TLV Type
Specifies the bandwidth reservation required at each LSR hop. Type value in the range 0x2F00 through 0x2FFF. Together, the Type
The encoding for the Bandwidth Reservation is: and Vendor Id field specify how the Data field is to be inter-
preted.
0 1 2 3 Length
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 Specifies the cumulative length in octets of the Vendor ID and Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ fields.
| Bandwidth TLV (0x0804) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BW requirement |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
BW Requirement Vendor Id
Unsigned 32 bit integer representing the bandwidth, in units of 802 Vendor ID as assigned by the IEEE.
kilo bps, that must be reserved for the LSP at every LSR identi-
fied in the ERNH Object. The bandwidth is guaranteed within a
coarser time period allowing for simpler implementations. The
specified bandwidth is guaranteed within several milliseconds or
a few seconds time period. Nodes may also use this as a minimal
bandwidth guarantee within the same time period.
3.4.12.1. Explicit Route Request Procedures Data
The remaining octets after the Vendor ID in the Value field are
optional vendor-dependent data.
See Sections "Explicitly Routing LSPs" and "ERLSP State Machine" for 3.6.1.2. LDP Vendor-private Messages
general procedures for handling the Explicit Route Request Message.
3.4.13. Explicit Route Response Message The Message Type range 0x2F00 through 0x2FFF is reserved for vendor-
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER Response (0x0501) | Message Length | |U| Msg Type (0x2F00-0x2FFF) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID | | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ERLSPID TLV | | Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV | + +
| Remaining Mandatory Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status TLV | | |
+ +
| Optional Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The encodings for the Label, and Status TLVs can be found in Section U bit
3.3.3 ("Commonly Used TLVs"). Unknown message bit. Upon receipt of an unknown message, if U is
clear (=0), a notification is returned to the message originator;
if U is set (=1), the unknown message is silently ignored.
Message Id The determination as to whether a vendor-private message is under-
Four octet integer used to identify this message. stood is based on the Msg Type and the Vendor ID parameter.
ERLSPID TLV Msg Type
The globally unique value used for ERLSPID in the Explicit Request Message type value in the range 0x2F00 through 0x2FFF. Together,
message that elicited this Response message. The encoding for the the Msg Type and the Vendor ID specify how the message is to be
ERLSPID (shown above and repeated here for convenience) is: interpreted.
0 1 2 3 Message Length
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 Specifies the cumulative length in octets of the Message ID, Vendor
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ID, Remaining Mandatory Parameters and Optional Parameters.
| ERLSPID (0x0801) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Explicit Identifier |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Peg Explicit Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Explicit Identifier Message ID
A 6-octet globally unique value that identifies the explicit 32-bit integer used to identify this message. Used by the sending
route LSP. It is generated by the LSR that creates the Explicit LSR to facilitate identifying notification messages that may apply
Request message. The first four octets is the LSR IP Address. to this message. An LSR sending a notification message in response
The last two octets contain a `Local identifier' value. It is to this message will include this Message Id in the notification
incumbent on an LSR that originates an Explicit Request message message; see Section "Notification Message".
to choose an unused value for the Local Identifier.
Peg Explicit Identifier Vendor ID
A 6-octet globally unique value that identifies a loose segment 802 Vendor ID as assigned by the IEEE.
of an explicit route LSP. It is generated by the upstream peg
LSR that creates the loose segment. The first four octets is the
LSR IP Address. The last two octets contain a 'Local identifier'
value. It is incumbent on a peg LSR that creates a loose segment
to choose an unused value for the Local Identifier every time the
segment is reestablished. When a segment is strictly routed this
field is set to zero by the sender and ignored by the receiver.
3.4.13.1. Explicit Route Respon