How are SRv6 SIDs used?

SRv6 SIDs

Segment routing IPv6 (SRv6) encodes 128-bit segment identifiers (SIDs) programmed as IPv6 addresses to provide tunnels to IPv6 destinations. SRv6 SIDs are an alternative to SR-MPLS SIDs. Three types of IGP-advertised SRv6 SIDs are supported:

END SIDs — Equivalent to Node SIDs, these are configured for Loopback interfaces from the static label range and are used as Loose Hops
END.X SIDs — Equivalent to Adjacency SIDs, these are configured or auto-generated for Network Interfaces and are used for Strict Hops
LAN END.X SIDs — Adjacency SIDs to ISIS neighbors over a broadcast interface, auto-generated when “end-x-auto-allocate” is configured on the node

NSP's path control views display SRv6 SIDs for links, nodes, and prefixes where applicable to enable robust routing and troubleshooting. Visibility of SRv6 SIDs on IGP links simplifies network management by enabling direct control over traffic routes, thereby improving network efficiency. In segment routing, both prefixes and nodes can be assigned the same type of SID, which acts as a universal identifier. This SID can be advertised through IGPs, simplifying the control plane as both types of entities use the same addressing and forwarding mechanism. By using the same SID for both prefixes and nodes, networks can more flexibly define end-to-end paths that include specific network segments and node hops. Advertising SIDs on prefixes enables routers to directly map traffic flows to optimal paths, significantly enhancing network efficiency and reducing latency. Integrating SIDs into IGP broadcasts allows for easier network management and supports advanced routing techniques without the need for additional protocols.

Note: The NSP requires that BGP-LS prefixes be marked with the 'redistributed' flag when they are re-advertised. This may not be enabled by default on routers. Users should consult the relevant router documentation to determine how to enable this flag.

SRv6 SIDs can be used with NSP's path finder function, the IETF topology API, the IGP Topology Discovery Service, and the NSP's path simulation function (when a 24.8 or later network is imported).

Each SRv6 SID contains a locator, which is displayed in the Routers list and on the network map, when a router is selected. Each router can have multiple locators for Algo 0 and different FlexAlgo IDs. When a router is selected on the Routers table on the network map, the locators for Algo 0 and FlexAlgos are displayed on the right hand side panel. The NSP's path finder function can also be used to find a SRv6 path for Algo 0 or for locator FlexAlgo IDs.

To allow for a larger number of SIDs, the NSP also supports the use of micro-SIDs (uSIDs) for END, END.X, and LAN END.X SIDs. These micro-SIDs are identified by their Endpoint behavior types and the suffix (uN for END SIDs and uA for END.X SIDs), which is visible in their prefix address.

Note: The IGP Topology Discovery service does not report SRv6 SIDs to the NSP's PostgreSQL database. Therefore, the RestConf API will not display any SRv6 SIDs.

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