Overview
Segment Routing (SR) is a source routing technology. The source node selects a path for the packets, and then encodes the segment identifiers (SIDs) of other nodes on the path in the packets. The nodes will process the arriving packets based on the SIDs in the packets. The source node can select any reachable path for the packets and only the source node needs to maintain the path status.
They are used to identify the following types of segments:
Prefix segment—Forwarding entries are created based on the prefix of the destination address in packets. The source node uses the shortest path to forward the packets. SIDs are assigned to other nodes according to the destination address prefix.
Adjacency segment—SIDs are assigned to nodes based on adjacency. The source node selects a path for the packets and encodes the SIDs of other nodes on the path in the packets.
SR can operate with MPLS. In an MPLS network, SR uses MPLS labels as SIDs for packet forwarding.