IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)
obsoletes
- rfc-4205 — Intermediate System to Intermediate System (IS-IS) Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)
updated by
- rfc-6001 — Generalized MPLS (GMPLS) Protocol Extensions for Multi-Layer and Multi-Region Networks (MLN/MRN)
- rfc-6002 — Generalized MPLS (GMPLS) Data Channel Switching Capable (DCSC) and Channel Set Label Extensions
- rfc-7074 — Revised Definition of the GMPLS Switching Capability and Type Fields
updates
- rfc-5305 — IS-IS Extensions for Traffic Engineering
Extracted elements (26)
Maximum and Minimum LSP Bandwidth fields throughout the ISCD sub-TLV are encoded in bytes per second (not bits per second) using IEEE 754 floating-point format. This is a non-obvious unit choice that implementors must handle correctly to avoid bandwidth miscalculation.
The Interface Switching Capability Descriptor sub-TLV is permitted to appear multiple times in a single extended IS reachability TLV because a single interface may have more than one switching capability (e.g., both packet and lambda switching), each requiring its own descriptor.
The SRLG TLV uses a separate top-level TLV (type 138) rather than a sub-TLV of the extended IS reachability TLV because SRLG membership is a link property that must be identified by both endpoints' System IDs, pseudonode number, and interface addresses, requiring more addressing context than a sub-TLV allows.
Support for unnumbered interfaces in GMPLS IS-IS extensions requires implementation of the Point-to-Point Three-Way Adjacency IS-IS Option type (RFC 5303), which carries the Extended Local Circuit ID used as the Link Identifier.
A restarting node SHOULD follow IS-IS restart procedures (RFC 5306) and RSVP-TE restart procedures (RFC 3473) when originating TE link LSPs.
If the Link Local/Remote Identifiers sub-TLV occurs more than once within the extended IS reachability TLV, the receiver SHOULD ignore all these sub-TLVs.
Neighbors of the restarting node SHOULD continue to advertise the actual unreserved bandwidth on TE links from the neighbors to that node during the restart period.
Prior to a planned restart, the restarting node SHOULD originate TE LSPs with 0 unreserved bandwidth, and 0 Max LSP Bandwidth for LSC/FSC links, to discourage new LSP establishment through the restarting router.
The Interface Switching Capability Descriptor sub-TLV MAY occur more than once within the extended IS reachability TLV, to support interfaces with more than one Interface Switching Capability Descriptor.
The Link Local/Remote Identifiers sub-TLV MUST NOT occur more than once within the extended IS reachability TLV.
The Link Protection Type sub-TLV MUST NOT occur more than once within the extended IS reachability TLV; if it does, the receiver SHOULD ignore all occurrences.
The second (Reserved) octet of the Link Protection Type sub-TLV SHOULD be set to zero by the sender and SHOULD be ignored by the receiver.
The SRLG TLV MAY occur more than once within the IS-IS Link State Protocol Data Units.
When originating TE link LSPs during restart, the restarting node SHOULD advertise 0 unreserved bandwidth and TE Default metric 0xffffff; for LSC or FSC links, Max LSP Bandwidth SHOULD be set to 0 until preserved LSP resources are accounted for.
For PSC-1/2/3/4 switching capability, the capability-specific information field includes Minimum LSP Bandwidth (4-octet IEEE float, bytes/sec) and Interface MTU (2-octet integer, bytes).
For TDM switching capability, the capability-specific information field includes Minimum LSP Bandwidth (4-octet IEEE float, bytes/sec) and a 1-octet indication: 0 = Standard SONET/SDH, 1 = Arbitrary SONET/SDH. For L2SC and LSC, no capability-specific field is present.
Link Identifiers for unnumbered interfaces are exchanged in the Extended Local Circuit ID field of the Point-to-Point Three-Way Adjacency IS-IS Option type (RFC 5303), not in any GMPLS-specific TLV.
The SRLG TLV Flags octet uses bit 0 (least significant) to indicate whether the interface is numbered (1) or unnumbered (0); all other bits are reserved and should be set to 0.
The Switching Capability field in the ISCD sub-TLV uses the following values: 1=PSC-1, 2=PSC-2, 3=PSC-3, 4=PSC-4, 51=L2SC, 100=TDM, 150=LSC, 200=FSC. The Encoding field references values from RFC 3471 Section 3.1.1.
This document registers three sub-TLV types for top-level TLV 22 in the IS-IS sub-TLV registry: type 4 (Link Local/Remote Identifiers, length 8), type 20 (Link Protection Type, length 2), and type 21 (Interface Switching Capability Descriptor, variable length).
This document registers TLV type 138 (Shared Risk Link Group / GMPLS-SRLG) in the IS-IS TLV codepoint registry, applicable in LSP PDUs only (not IIH or SNP).
GMPLS TE TLVs are not used for SPF computation or normal IP routing, so these extensions have no direct effect on IP routing. However, tampering with GMPLS TE TLVs may affect the underlying optical and/or SONET/SDH transport network. IS-IS cryptographic authentication mechanisms (RFC 5304) can be used to secure these TLVs.
The Interface Switching Capability Descriptor sub-TLV (type 21) encodes: 1-octet Switching Cap, 1-octet Encoding, 2-octet Reserved, eight 4-octet IEEE floating-point Max LSP Bandwidth fields (priorities 0–7, in bytes/sec), and variable Switching Capability-specific information.
The Link Local/Remote Identifiers sub-TLV (type 4) has a fixed length of 8 octets: 4 octets of Link Local Identifier followed by 4 octets of Link Remote Identifier. If the Link Remote Identifier is unknown, it is set to 0.
The Link Protection Type sub-TLV (type 20) is 2 octets: the first octet is a bit vector of protection capabilities (0x01=Extra Traffic, 0x02=Unprotected, 0x04=Shared, 0x08=Dedicated 1:1, 0x10=Dedicated 1+1, 0x20=Enhanced); the second octet is reserved.
The SRLG TLV (type 138) encodes: 6-octet System ID, 1-octet Pseudonode Number, 1-octet Flags, 4 octets of IPv4 interface address or Link Local Identifier, 4 octets of IPv4 neighbor address or Link Remote Identifier, followed by a variable-length list of 4-octet SRLG values. Total length = 16 + 4*(number of SRLG values).