Supported Platforms
Detour Computations
Computing and setting up detours is done independently at each node. On a node, if an LSP has fast reroute enabled and if a downstream link or node can be identified, the router or switch performs a Constrained Shortest Path First (CSPF) computation using the information in the local traffic engineering database. For this reason, detours rely on your IGP supporting traffic engineering extensions. Without the traffic engineering database, detours cannot be established.
CSPF initially attempts to find a path that skips the next downstream node. Attempting to find this path provides protection against downstream failures in either nodes or links. If a node-skipping path is not available, CSPF attempts to find a path on an alternate link to the next downstream node. Attempting to find an alternate link provides protection against downstream failures in links only. Detour computations might not succeed the first time. If a computation fails, the router recomputes detours approximately once every refresh interval until the computation succeeds. The RSVP metric for each detour is set to a value in the range from 10,000 through 19,999.
