Information About SSPF with Segment Routing
Strict Shortest Path First
Segment Routing supports the following two algorithms:
Algorithm 0: This is a Shortest Path First (SPF) algorithm based on link metric. This shortest path algorithm is computed by the Interior gateway protocol (IGP).
Algorithm 1: This is a Strict Shortest Path First (SSPF) algorithm based on link metric. The algorithm 1 is identical to algorithm 0 but requires that all nodes along the path honor the SPF routing decision. Local policy does not alter the forwarding decision. For example, a packet is not forwarded through locally engineered path.
Different SIDs are associated with the same prefix for each algorithm.
Strict Shortest Path First is supported by default - but strict SIDs must be configured for at least one node address on each node supporting Segment Routing.
Approaches for Configure Strict Shortest Path First
The two approaches to configure Strict SFP are as follows:
Using the connect-prefix-sid-map command—Strict SFP is configured globally on all the nodes. For a network to be Strict SFP-aware (that is, for ISIS to populate Strict SPF), all nodes must be configured with a local Strict SFP SID.
Using Segment-routing Mapping Server—One node in the network is configured as mapping server and the remaining nodes act as a client.