Forwarding Example with SIDs
Figure 1-1 shows an example of forwarding a packet using a prefix SID.
Figure 1-1: Forwarding example
1. If ingress node R1 receives packet destined for R7 with no SR label stack in packet header, the packet will get forwarded to R7 along the IGP shortest-path (R1-R2-R3-R7).
2. If the packet was received with SR label stack of [16005], R1 inspects the top label which is 16005. 16005 is the node SID associated with R5 and so this tells R1 to forward the packet along IGP shortest-path to R5 (R1-R2-R5 or R1-R4-R5). The next hop node (R2 or R4) does the same action as R1. On receiving the packet, R5 inspects the top label which is 16005 and since it matches its node SID, it pops the top label. There are no more labels in the stack and R5 forwards the packet to R7 along the IGP shortest-path (R5-R6-R7).
3. If the packet was received with SR label stack of [16006, 24067], R1 inspects the top label which is 16006 and because that is the node SID associated with R6, R1 forwards the packet along the IGP shortest-path to R6 (R1-R2-R3-R6, R1-R2-R5-R6 or R1-R4-R5-R6). R6 inspects the top label which is 16006 and because it matches its node SID, R6 pops the top label and inspects the next label which is 24067. 24067 is the adjacency SID associated with R6's adjacency with R7 so this tells R6 to pop the label and forward the packet over its link connected to R7.
Last modified date: 06/27/2023