LDP, Label Distribution Protocol

Description Glossary RFCs Publications Obsolete RFCs


Protocol suite:ATM, TCP/IP.
Protocol type:Application layer protocol.
Port:646 (TCP, UDP).
MIME subtype:
SNMP MIBs: iso.org.dod.internet.mgmt.mib-2.transmission.mplsStdMIB (
iso.org.dod.internet.mgmt.mib-2.transmission.mplsStdMIB.MPLS-LDP-STD-MIB (
iso.org.dod.internet.mgmt.mib-2.transmission.mplsStdMIB.MPLS-LDP-ATM-STD-MIB (
iso.org.dod.internet.mgmt.mib-2.transmission.mplsStdMIB.MPLS-LDP-FRAME-RELAY-STD-MIB (
iso.org.dod.internet.mgmt.mib-2.transmission.mplsStdMIB.MPLS-LDP-GENERIC-STD-MIB (
Working groups:
Links: IANA: LDP name spaces.

MAC header IP header TCP | UDP header LDP header Data :::

LDP header:

0001020304050607 0809101112131415 1617181920212223 2425262728293031
Version Length
Label space Data :::

Version. 16 bits.
Version number of the protocol.

Length. 16 bits.
Total size of this message in bytes excluding the Version and Length fields. The maximum allowable length is negotiable when an LDP session is initialized. Prior to completion of the negotiation the maximum allowable length is 4096 bytes.

LSR ID, Label Switched Router ID. 32 bits.

Label space. 16 bits.

Data. Variable length.

TLV record:

0001020304050607 0809101112131415 1617181920212223 2425262728293031
U F Type TLV length
Value :::

U, Unknown TLV. 1 bit.

0 A notification must be returned to the message originator and the entire message must be ignored.
1 The unknown TLV is silently ignored and the rest of the message is processed as if the unknown TLV did not exist.

F, Forward unknown TLV. 1 bit.
Valid only when the U bit is set and the LDP message containing the unknown TLV is to be forwarded.

0The unknown TLV is not forwarded with the containing message.
1The unknown TLV is forwarded with the containing message.

Type. 14 bits.

0x0100FEC. RFC 3036, RFC 5036
0x0101Address List. RFC 3036, RFC 5036
0x0103Hop Count. RFC 3036, RFC 5036
0x0104Path Vector. RFC 3036, RFC 5036
0x0200Generic Label. RFC 3036, RFC 5036
0x0201ATM Label. RFC 3036, RFC 5036
0x0202Frame Relay Label. RFC 3036, RFC 5036
0x0203FT Protection TLV.RFC 3479
0x0300Status. RFC 3036, RFC 5036
0x0301Extended Status. RFC 3036, RFC 5036
0x0302Returned PDU. RFC 3036, RFC 5036
0x0303Returned Message. RFC 3036, RFC 5036
0x0400Common Hello Parameters. RFC 3036, RFC 5036
0x0401IPv4 Transport Address. RFC 3036, RFC 5036
0x0402Configuration Sequence Number. RFC 3036, RFC 5036
0x0403IPv6 Transport Address. RFC 3036, RFC 5036
0x0500Common Session Parameters. RFC 3036, RFC 5036
0x0501ATM Session Parameters. RFC 3036, RFC 5036
0x0502Frame Relay Session Parameters. RFC 3036, RFC 5036
0x0503FT Session TLV.RFC 3479
0x0504FT Ack TLV.RFC 3479
0x0505FT Cork TLV.RFC 3479
0x0600Label Request Message ID. RFC 3036, RFC 5036
0x0601MTU. RFC 3988
0x0800Explicite Route. RFC 3212
0x0801IPv4 Prefix ER-Hop. RFC 3212
0x0802IPv6 Prefix ER-Hop. RFC 3212
0x0803Autonomous System Number ER-Hop. RFC 3212
0x0804LSP-ID ER-HOP. RFC 3212
0x0810Traffic Parameters. RFC 3212
0x0820Preemption. RFC 3212
0x0821LSPID. RFC 3212
0x0822Resource Class. RFC 3212
0x0823Route Pinning. RFC 3212
0x0824Generalized Label Request. RFC 3472
0x0825Generalized Label. RFC 3472
0x0826Upstream Label. RFC 3472
0x0827Label Set.RFC 3472
0x0828Waveband Label.RFC 3472
0x0829ER-Hop.RFC 3472
0x082AAcceptable Label Set.RFC 3472
0x082BAdmin Status.RFC 3472
0x082CInterface ID.RFC 3472
0x082DIPv4 Interface ID.RFC 3472
0x082EIPv6 Interface ID.RFC 3472
0x082FIPv4 IF_ID Status.RFC 3472
0x0830IPv6 IF_ID Status.RFC 3472
0x0831Op-Sp Call ID.RFC 3475
0x0832GU Call ID.RFC 3475
0x0833Call Capability.RFC 3475
0x0834Crankback.RFC 3475
0x0835Protection.RFC 3472
0x0837Unnumbered Interface ID.RFC 3480
0x0838SONET/SDH Traffic Parameters.RFC 3946
0x0901Diff-Serv.RFC 3270
0x0960IPv4 Source ID.RFC 3476
0x0961IPv6 Source ID.RFC 3476
0x0962NSAP Source ID.RFC 3476
0x0963IPv4 Destination ID.RFC 3476
0x0964IPv6 Destination ID. RFC 3476
0x0965NSAP Destination ID. RFC 3476
0x0966Egress Label. RFC 3476
0x0967Local Connection ID. RFC 3476
0x0968Diversity. RFC 3476
0x0969Contract ID. RFC 3476
0x096APW Status. RFC 4447
0x096BPW Interface Parameters. RFC 4447
0x096CGroup ID. RFC 4447
0x096EBandwidth TLV. 
0x0970UNI Service Level. RFC 3476

TLV length. 16 bits.
Size of the Value field in bytes.

Value. Variable length.

Message name space:

0x0001Notification. RFC 3036
0x0100Hello. RFC 3036
0x0200Initialization. RFC 3036
0x0201KeepAlive. RFC 3036
0x0300Address. RFC 3036
0x0301Address Withdraw. RFC 3036
0x0400Label Mapping. RFC 3036
0x0401Label Request. RFC 3036
0x0402Label Withdraw. RFC 3036
0x0403Label Release. RFC 3036
0x0404Label Abort Request. RFC 3036
0x0500Call Setup. RFC 3475
0x0501Call Release. RFC 3475
Vendor private extensions. 
Experimental extensions. 



[RFC 3036] LDP Specification.

[RFC 3037] LDP Applicability.

[RFC 3038] VCID Notification over ATM link for LDP.

[RFC 3212] Constraint-Based LSP Setup using LDP.

[RFC 3213] Applicability Statement for CR-LDP.

[RFC 3214] LSP Modification Using CR-LDP.

[RFC 3215] LDP State Machine.

[RFC 3270] Multi-Protocol Label Switching (MPLS) Support of Differentiated Services.

[RFC 3472] Generalized Multi-Protocol Label Switching (GMPLS) Signaling Constraint-based Routed Label Distribution Protocol (CR-LDP) Extensions.

[RFC 3475] Documentation of IANA assignments for Constraint-Based LSP setup using LDP (CR-LDP) Extensions for Automatic Switched Optical Network (ASON).

[RFC 3478] Graceful Restart Mechanism for Label Distribution Protocol.

[RFC 3479] Fault Tolerance for the Label Distribution Protocol (LDP).

[RFC 3480] Signalling Unnumbered Links in CR-LDP (Constraint-Routing Label Distribution Protocol).

[RFC 3612] Applicability Statement for Restart Mechanisms for the Label Distribution Protocol (LDP).

[RFC 3815] Definitions of Managed Objects for the Multiprotocol Label Switching (MPLS), Label Distribution Protocol (LDP).

[RFC 3946] Generalized Multi-Protocol Label Switching (GMPLS) Extensions for Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) Control.

[RFC 3988] Maximum Transmission Unit Signalling Extensions for the Label Distribution Protocol.

[RFC 4221] Multiprotocol Label Switching (MPLS) Management Overview.

[RFC 4447] Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP).


Obsolete RFCs:

Description Glossary RFCs Publications Obsolete RFCs