Loop-Free Alternate (LFA) Fast Reroute (FRR)
Loop-Free Alternate Fast Reroute is a mechanism that allows dynamic routing protocols to quickly switch (within 50 ms) to a backup path when a primary path fails. Without LFA FRR, protocols such as OSPF must re-run their routing algorithm to find a new path when the primary path fails. With LFA FRR, a backup path is precomputed and is installed as a backup next hop in the forwarding table.
If the alternate paths have the same metric and are loop free, then a series of tie breakers is used to determine the backup path.
You can calculate LFA per prefix or per link. The explanation is here:
Difference between per-prefix LFA and per-link based LFA
Here is an overview of (routing) protocols with LFA FRR support:
Links: