A customer reports that each time a networking component fails, OSPF recalculates the backup path, with causes a short outage. Which solution must the customer implement to improve this situation?
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.
Option B is the correct answer because LFA FRR is a technique that provides a fast, local reroute for link and node failures in OSPF networks. It uses precomputed backup paths that avoid the failed component and ensure loop-free convergence in less than 50 milliseconds. This ensures that there is no disruption to traffic during the time that OSPF recalculates the new path.
I'm going with B because LFA FRR require no re-calculation of the backup path. While true Incremental SPF reduces the potential outage time, it still needs to re-calculate a backup path which is why B is the more correct answer to me.
OSPF Loop-Free Alternate (LFA) Fast Reroute (FRR) - repair route implemented by CEF
https://networklessons.com/cisco/ccie-routing-switching-written/ospf-loop-free-alternate-lfa-fast-reroute-frr
"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."
I find that "Incremental SPF" is used to decrease CPU load upon recalculation, but how does it help in reducing outage time?
I am leaning towards LFA FRR, as "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." (https://networklessons.com/cisco/ccie-routing-switching-written/ospf-loop-free-alternate-lfa-fast-reroute-frr)
from the link shared above: "Incremental SPF allows the system to recompute only the affected part of the tree. Recomputing only a portion of the tree rather than the entire tree results in faster OSPF convergence and saves CPU resources" - so it should reduce the outage as well
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