Which two components does the IS-IS IPv4 Loop-Free Alternate Fast Reroute feature fail to protect? (Choose two.)
IS-IS (Intermediate System to Intermediate System) is a routing protocol used in Service Provider networks. The Loop-Free Alternate (LFA) Fast Reroute (FRR) feature is used to provide a backup path in case of a link or node failure. This feature helps to reduce packet loss and minimize the convergence time in case of a failure.
However, there are certain scenarios where the IS-IS IPv4 LFA FRR feature fails to provide protection. Let's discuss the two components that are not protected by this feature:
ECMP (Equal Cost Multi-Path) paths: IS-IS IPv4 LFA FRR feature does not protect ECMP paths. When multiple paths with the same cost exist between the source and destination, the router can load-balance traffic across these paths. If one of the paths fails, traffic is rerouted to the backup path. However, if all the paths fail, the traffic is dropped. In this scenario, the IS-IS IPv4 LFA FRR feature cannot provide protection.
MPLS TE (Traffic Engineering) tunnels: IS-IS IPv4 LFA FRR feature does not protect MPLS TE tunnels. MPLS TE tunnels are used to provide traffic engineering capabilities in Service Provider networks. These tunnels are established between the ingress and egress routers, and the traffic is forwarded through the tunnels based on the path defined by the network operator. If the primary path fails, the traffic is rerouted through the backup path. However, if the backup path is also protected by IS-IS IPv4 LFA FRR, then the backup path may not be available, and the traffic will be dropped.
Therefore, the answer is A. ECMP and E. MPLS TE tunnels. The IS-IS IPv4 LFA FRR feature provides protection to port channels, downstream paths, and subinterfaces.