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Beginner

Difference between LFA and FRR

Hello experts!

I have troubles in understanding what is the difference between these two technologies in MPLS networks.
Are they used for the same thing? (assuring backup path)
Or maybe FRR uses LFA for calculating paths?

If we use FRR with RSVP-TE, do we need LFA?
I would be glad of any clarifications on this topic.

2 REPLIES 2
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Cisco Employee

Both IP FRR (LFA) and RSVP-TE FRR have same purpose i.e. to Fast ReRoute the traffic to a back up path in case of primary link/node/path failures. If you use RSVP TE you donot need LFA.

  • IP FRR doesn't use RSVP to presignal a back up tunnel. It simply uses your IGP (OSPF /  ISIS).
  • By default IGP calculates the best path to a particular destination and installs the route in the RIB and FIB.
  • When IP FRR (LFA) is enabled on the IGP, along with a primary path it also calculates a back up path and install it as back up path in RIB and FIB but the back up path is not used for traffic forwarding till we have a failure.
  • Because we have the back up path pre-caluclated and installed in RIB and FIB(it takes the longest time) switchingover to back up path in case of a failure is very quick.
  • IP FRR can achieve the same protection times like RSVP-TE FRR (50ms) with out much overhead of creating back up tunnels and RSVP signalling etc.

 

You can have a look at this for more details

   https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pi/configuration/xe-3s/iri-xe-3s-book/iri-ip-lfa-frr.html

   https://learningnetwork.cisco.com/thread/117782

 

regards

Ashish

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Thank you Ashish for your answer! So to summarize. In IP networks we use IP FRR (LFA). [additionall path in FIB] In LDP enabled MPLS networks we use FRR LFA. [additional labels in LFIB] In RSVP-TE MPLS networks we use RSVP FRR. [additional RSVP tunnels] Is that correct?