2017-12-18 2026-03-21 Standards Action 0 Shortest Path First (SPF) algorithm based on link metric. This is the standard shortest path algorithm as computed by the IGP protocol. Consistent with the deployed practice for link-state protocols, Algorithm 0 permits any node to overwrite the SPF path with a different path based on its local policy. 1 Strict Shortest Path First (SPF) algorithm based on link metric. The algorithm is identical to Algorithm 0 but Algorithm 1 requires that all nodes along the path will honor the SPF routing decision. Local policy at the node claiming support for Algorithm 1 MUST NOT alter the SPF paths computed by Algorithm 1. 2-127 Unassigned 128-255 Flexible Algorithms RFC9350, Section 4 Expert Review Uma Chunduri, Jeff Tantsura When this registry is modified, the YANG module "iana-msd-type" must be updated as defined in . 0 Reserved 1 Base MPLS Imposition MSD MPLS 2 ERLD-MSD MPLS 3 Readable Label Depth MPLS 4-40 Unassigned 41 SRH Max SL SRv6 42 SRH Max End Pop SRv6 43 Unassigned 44 SRH Max H.encaps SRv6 45 SRH Max End D SRv6 46-250 Unassigned 251-254 Experimental Use 255 Reserved Expert Review Les Ginsberg, Chris Hopps 0 RSVP-TE (R-bit) 1 Segment Routing Policy (S-bit) 2 Loop-Free Alternate (F-bit) 3 Flexible Algorithm (X-bit) RFC9350, Section 12 4-63 Unassigned 0-127 Standards Action 128-255 User-Defined Metric 0 IGP Metric RFC9350, Section 5.1 No 1 Min Unidirectional Link Delay as defined in RFC8570, Section 4.2 and RFC7471, Section 4.2 RFC9350, Section 5.1 No 2 Traffic Engineering Default Metric as defined in RFC5305, Section 3.7 and Traffic Engineering Metric as defined in RFC3630, Section 2.5.5 RFC9350, Section 5.1 No 3 Bandwidth Metric Yes 4-127 Unassigned 128-255 Reserved for User-Defined Metric Yes Standards Action 0 Prefix Metric Flag (M-flag) RFC9350, Sections 6.4 and 7.4 IETF Review 0 Path computation with GMPLS link constraints 1 Bidirectional path computation 2 Diverse path computation 3 Load-balanced path computation 4 Synchronized paths computation 5 Support for multiple objective functions 6 Support for additive path constraints (max hop count, etc.) 7 Support for request prioritization 8 Support for multiple requests per message 9 Global Concurrent Optimization (GCO) 10 P2MP path computation 11 Active stateful PCE capability 12 Passive stateful PCE capability 13 Active Stateful PCE with P2MP 14 Passive Stateful PCE with P2MP 15 Stateful PCE Initiation with P2MP 16 FlowSpec 17 TCP-AO Support 18 PCEP over TLS support 19-31 Unassigned Standards Action 0 Reserved 1 PCE-ADDRESS 2 PATH-SCOPE 3 PCE-DOMAIN 4 NEIG-PCE-DOMAIN 5 PCE-CAP-FLAGS 6 KEY-ID 7 KEY-CHAIN-NAME 8-65535 Unassigned Expert Review Unassigned 0 Reserved for centralized mode 1-127 Unassigned 128-254 Reserved for Private Use 255 Reserved Expert Review Peter Psenak, Shraddha Hegde 1 Check if any exclude Administrative Group rule is part of the Flex-Algorithm Definition. If such exclude rule exists, check if any color that is part of the exclude rule is also set on the link. If such a color is set, the link MUST be pruned from the computation. RFC9350, Section 13 2 Check if any exclude SRLG rule is part of the Flex-Algorithm Definition. If such exclude rule exists, check if the link is part of any SRLG that is also part of the SRLG exclude rule. If the link is part of such SRLG, the link MUST be pruned from the computation. RFC9350, Section 13 3 Check if any include-any Administrative Group rule is part of the Flex-Algorithm Definition. If such include-any rule exists, check if any color that is part of the include-any rule is also set on the link. If no such color is set, the link MUST be pruned from the computation. RFC9350, Section 13 4 Check if any include-all Administrative Group rule is part of the Flex-Algorithm Definition. If such include-all rule exists, check if all colors that are part of the include-all rule are also set on the link. If all such colors are not set on the link, the link MUST be pruned from the computation. RFC9350, Section 13 5 If the Flex-Algorithm Definition uses something other than the IGP metric (Section 5 of ), and such metric is not advertised for the particular link in a topology for which the computation is done, such link MUST be pruned from the computation. A metric of value 0 MUST NOT be assumed in such a case. RFC9350, Section 13 6 Check if any exclude FAEMB rule is part of the Flex-Algorithm definition. If such exclude rule exists and the link has Maximum Link Bandwidth advertised, check if the link bandwidth satisfies the FAEMB rule. If the link does not satisfy the FAEMB rule, the link MUST be pruned from the Flex-Algorithm computation. RFC9843, Section 6 7 Check if any exclude FAEMD rule is part of the Flex-Algorithm definition. If such exclude rule exists and the link has Min Unidirectional link delay advertised, check if the link delay satisfies the FAEMD rule. If the link does not satisfy the FAEMD rule, the link MUST be pruned from the Flex-Algorithm computation. RFC9843, Section 6 8 Check if any exclude reverse Admin Group rule is part of the Flex-Algorithm definition. If such exclude rule exists, check if any Admin Group that is part of the exclude rule is also set on the link in the reverse direction. If such Admin Group is set on the link in the reverse direction, the link MUST be pruned from the computation. RFC9917, Section 11 9 Check if any include-any reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-any rule exists, check if any Admin Group that is part of the include-any rule is also set on the link in the reverse direction. If no such Admin Group is set on the link in the reverse direction, the link MUST be pruned from the computation. RFC9917, Section 11 10 Check if any include-all reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-all rule exists, check if all Admin Groups that are part of the include-all rule are also set on the link in the reverse direction. If all such Admin Groups are not set on the link in the reverse direction, the link MUST be pruned from the computation. RFC9917, Section 11