SRLSP

Segment routing label switched paths (SRLSPs) are special CRLSPs established based on SR. An MPLS TE tunnel can contain one or multiple SRLSPs. When a packet arrives, the source node (ingress node) forwards the packet through the SRLSPs if its output interface is the MPLS TE tunnel interface.

The device supports only static SRLSPs established by using the adjacency method. You must configure the outgoing labels on the ingress node and the incoming labels and other constraints on all transit nodes that the traffic flow traverses.

Figure 83 shows how a static SRLSP forwards a packet.

  1. Ingress node Device A adds a label stack to the packet and then forwards it to Device B.

    The label stack is an ordered list of adjacency SIDs of the nodes that the SRLSP traverses: 201, 202, and 203.

  2. When Device B receives the packet, it removes the top label of the label stack (label 201) and then forwards the packet to the next node Device C.

  3. When Device C receives the packet, it removes the top label of the label stack (label 202) and then forwards the packet to the next node Device D.

  4. When Device D receives the packet, it removes the last label (label 203) of the packet and then forwards the packet (an IP packet) to Device E (the egress node).

  5. When egress node Device E receives the packet, it forwards the packet to the destination IP address.

Figure 83: How a static SRLSP forwards a packet (adjacency method)