The FRR MPLS facility backup method and one-to-one backup method are configured on the ingress LER (iLER) by using the fast-reroute command.
The behavior of an LSP at an iLER with both FRR and a standby LSP path configured is as follows.
When a downstream detour route (alternative path) becomes active at a Point of Local Repair (PLR):
The iLER switches to the standby LSP path as soon as it is notified of the reroute. If the primary LSP path is subsequently repaired at the PLR, the LSP switches back to the primary path. If the standby path goes down, the LSP is switched back to the primary path, even though the primary path is still on the detour route at the PLR.
If the primary path goes down at the iLER while the LSP is on the standby path, the detour route at the iLER is torn down and, for one-to-one backup detour routes, a ‟path tear” is sent for the detour route. In other words, the detour route at the iLER does not protect the standby LSP. If and when the primary LSP is again successfully resignaled, the iLER detour route will be restarted.
When the primary LSP fails at the iLER:
The LSP switches to the detour route. If the primary path undergoes a global revertive recovery, the LSP switches back to the primary path. If the LSP is on the detour route and the detour route fails, the LSP is switched to the standby path.
Administrative groups are not taken into account when creating the detour routes for LSPs.