LFA (Loop free alternate)
What is concept of LFA (Loop free alternate)? and How actually it work and where we implement to real scenario Loop Free Alternates (LFA) is a mechanism by which a neighbor can be used as a backup next hop to provide a local repair path for the traffic to flow temporarily in case of failures in the primary next hop (node or link).For this the basic requirement is that the selected backup neighbor provides a loop free path with respect to primary next hop towards a destination originating a set of IGP prefixes. In certain topologies and usage scenarios, it may be possible that multiple destinations are originating the same prefix and there is no viable LFA to the best prefix originator, whilst a non-best prefix originator has one. Per prefix LFA is a mechanism by which LFA to a non-best prefix originator can be used in lieu of the LFA to the best prefix originator to provide local repair. In such cases, per prefix LFA can be used to increase the local repair coverage for the OSPF protocol. OSPF Loop-Free Alternate (LFA) Fast Reroute (FRR) allows OSPF to quickly switch (within 50 ms) to a backup path when a primary path fails. Without LFA FRR, OSPF has to re-run SPF to find a new path when the primary path fails. With LFA FRR, OSPF pre-computes a backup path and installs the backup next hop in the forwarding table.
Please see below picture for topology Loop Free Alternate (LFA) is a mechanism by which neighbours can be used as backup hops which are then used to provide a local fix path for traffic flowing in the event of a failure on the next main hop (node or link). LFA Fast Reroute allows OSPF to quickly switch to a backup path when a primary path fails. Without LFA FRR, OSPF has to re-run SPF to find a new path when the primary path fails. With LFA FRR, OSPF pre-computes a backup path and installs the backup next hop in the forwarding table. When a primary path breaks, LFA Fast Reroute enables OSPF to swiftly move to a backup link. When the primary path breaks without LFA FRR, OSPF must restart SPF to locate a new path. OSPF pre-calculates a backup path when using LFA FRR, and it puts the backup next hop in the forwarding table. OSPF may swiftly transition to a backup path when a primary path fails thanks to LFA Fast Reroute. When the primary path fails, OSPF would need to restart SPF in order to find a new path without LFA FRR. When using LFA FRR, OSPF pre-calculates a backup path and inserts the backup next hop into the forwarding table. OSPF Loop-Free Alternate (LFA) Fast Reroute (FRR) allows OSPF to quickly switch (within 50 ms) to a backup path when a primary path fails. Without LFA FRR, OSPF has to re-run SPF to find a new path when the primary path fails. With LFA FRR, OSPF pre-computes a backup path and installs the backup next hop in the forwarding table. OSPF Loop-Free AlternateFast Reroute allows OSPF to quickly switch (within 50 ms) to a backup path when a primary path fails. Without LFA FRR, OSPF has to re-run SPF to find a new path when the primary path fails. With LFA FRR, OSPF pre-computes a backup path and installs the backup next hop in the forwarding table. LFA Fast Reroute allows OSPF to quickly switch to a backup path when a primary path fails. Without LFA FRR, OSPF has to re-run SPF to find a new path when the primary path fails. With LFA FRR, OSPF pre-computes a backup path and installs the backup next hop in the forwarding table