Usage Scenario
By default, IS-IS supports TI-LFA path computation at the same level, but does not support cross-level path computation. If a Level-1 loop is open and no Level-1 backup path is available, TI-LFA FRR cannot be implemented in Level-1. After this command is enabled, a Level-2 path can be used to protect the Level-1 primary path, ensuring that the convergence time of FRR switching is within 50 ms.