When BGP fast reroute is enabled, BGP decides when a primary path is no longer usable and notifies the IOM. Based on BGP input, the IOM immediately reroutes affected traffic to the backup path.
When BGP fast reroute is enabled, the IOM reroutes traffic onto a backup path based on input from BGP. When BGP decides that a primary path is no longer usable, it notifies the IOM and affected traffic is immediately switched to the backup path.
The following events trigger failure notifications to the IOM and traffic rerouting to backup paths:
peer IP address is unreachable and peer tracking is enabled
BFD session associated with the BGP peer goes down
BGP session is terminated with the peer (for example, send or receive NOTIFICATION)
there is no longer any route (allowed by the next-hop resolution policy, if configured) that can resolve the BGP next-hop address
BGP tunnel that resolves the next hop goes down because the BGP label-IPv4 route is withdrawn by the peer or becomes invalid due to an unresolved next hop