Supported Platforms
Fast Reroute Path Optimization
A fast reroute protection path is nondeterministic. The actual protection path of a particular node depends on the history of the LSP and the network topology when the fast reroute path was computed. The lack of deterministic behavior can lead to operational difficulties and poorly optimized paths after multiple link flaps in a network. Even in a small network, after a few link flaps fast reroute paths can traverse an arbitrarily large number of nodes and can remain in that state indefinitely. This is inefficient and makes the network less predictable.
Fast reroute optimization addresses this deficiency. It provides a global path optimization timer, allowing you to optimize all LSPs that have fast reroute enabled and a detour path up and running. The timer value can be varied depending on the expected RE processing load.
The fast reroute optimization algorithm is based on the IGP metric only. As long as the new path’s IGP metric is lower than the old path’s, the CSPF result is accepted, even if the new path might be more congested (higher bandwidth utilization) or traverses more hops.
In conformance with RFC 4090, Fast Reroute Extensions to RSVP-TE for LSP Tunnels, when a new path is computed and accepted for fast reroute optimization, the existing detour is destroyed first and then the new detour is established. To prevent traffic loss, detours actively protecting traffic are not optimized.
