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Advantages of per link LFA over per prefix LFA
A. Per Link LFA
. Simpler computation – single rSPF per protected neighbour
. No prefix processing
. Less CPU/Memory intensive
. Smaller coverage
B. Per-Prefix LFA
. More complex computation – full Dijkstra per neighbour
. Per prefix backup computation
. More CPU/memory intensive
. Better Coverage
. Better controlled backup selection from the available set of backups
C.
D.
Correct Answer: A
Explanation/Reference:
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pi/configuration/xe-3s/iri-xe-3s-book/iri-ip-lfa-frr.pdf
Advantages of using per-prefix LFAs are as follows:
+ The repair path forwards traffic during transition when the primary path link is down.
+ All destinations having a per-prefix LFA are protected. This leaves only a subset (a node at the far side of the failure) unprotected.
Prefix-based LFAs allow computing backup information per prefix. Thus, repair/backup info computed for a given prefix using prefix-based LFA may be different than one computed by per-link LFA.
. More complex computation – full Dijkstra per neighbour
. Per prefix backup computation
. More CPU/memory intensive
. Better Coverage
. Better controlled backup selection from the available set of backups
In link-based LFAs, all prefixes reachable through the primary (protected) link share the same backup information. This means that the whole set of prefixes sharing the same primary also share the repair/FRR ability.
. Simpler computation – single rSPF per protected neighbour
. No prefix processing
. Less CPU/Memory intensive
. Smaller coverage
