Configuring IS-IS FRR
A link or router failure on a path can cause packet loss and routing loop. IS-IS FRR enables fast rerouting to minimize the failover time.
Figure 42: Network diagram for IS-IS FRR
In Figure 42, after you enable FRR on Router B, IS-IS automatically calculates or designates a backup next hop when a link failure is detected. In this way, packets are directed to the backup next hop to reduce traffic recovery time. Meanwhile, IS-IS calculates the shortest path based on the new network topology, and forwards packets over the path after network convergence.
You can assign a backup next hop for IS-IS FRR through the following ways:
Enable IS-IS FRR to calculate a backup next hop through Loop Free Alternate (LFA) calculation.
Designate a backup next hop with a routing policy for routes matching specific criteria.