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SRv6 TI-LFA FRR
Conventional loop-free alternate (LFA) requires that at least one neighbor be a loop-free next hop to a destination. Remote LFA (RLFA) requires that there be at least one node that connects to the source and destination nodes along links without passing through any faulty node. Unlike LFA or RLFA, Topology-Independent Loop-free Alternate FRR (TI-LFA) uses an explicit path to represent a backup path, which poses no topology constraints and provides more reliable fast reroute (FRR).
SRv6 TI-LFA
In Figure 3-53, if the P space and Q space do not intersect, RLFA requirements fail to be fulfilled, and RLFA cannot compute a backup path. If a fault occurs on the link between DeviceB and DeviceE, DeviceB forwards data packets to DeviceC. DeviceC is not a Q node and has no FRR entry directly to the destination IP address of DeviceF. In this situation, DeviceC has to recompute a path. The cost of the link between DeviceC and DeviceD is 1000. DeviceC considers that the optimal path to DeviceF passes through DeviceB. Therefore, DeviceC transmits the packet back to DeviceB, leading to a loop and resulting in a forwarding failure.
TI-LFA FRR provides link and node protection for SRv6. Figure 3-54 shows how SRv6 TI-LFA FRR is implemented.
