07-19-2013 07:08 PM - edited 03-01-2019 02:41 PM
what is the concept behind fast reroute in IS-IS
as it is not working for some of my devices in the network
Can someone explain what parameters of is-is have to met in order to make complete working fast re-route topology??
Solved! Go to Solution.
07-22-2013 07:32 AM
Ok in your topology IPFRR will partially work
Example let's say P3 is rotuing via P1 to reach PE2
In the case of P1-PE1 link faulre P1 can not use p3 as a loop free frr because igp still not converged and p3 still using p1 to reach pe2
What you can do is multi home PE3 and PE1 to both P1 and P3 to get around this limitation
Other option is if your network is mpls enabled you may read about remote LFA with LDP which can help you here
Hope this help
07-22-2013 12:10 PM
Check out this link
http://www.cisco.com/en/US/docs/wireless/asr_901/Configuration/Guide/remote_lfa-frr.html
Hope this help, if helpful rate
07-22-2013 10:25 PM
ok as per my example above
if P1 pre compute a back up path via P3 to reach PE2 prefixes and in a normal state P3 uses P1 to reach PE2 prefixes
then at the moment of failure if P1 uses P3 before ISIS converge P3 still uses P1 to reach these prefixes and this will form a loop
however if P1 uses P3 as a back path to reach P4-PE4 subnet then P1 can route via P3 as P3 dose not use P1 to reach this subbent and will not form a loop
hope this help
07-21-2013 09:10 AM
I think your referring here to lfa with isis
Can you share your topology and how are doing it
07-21-2013 09:31 AM
LFA/ipfrr works with 70 to 90% of topologies that's why we need to look at your topology and the path/prefix to be protected
07-22-2013 06:16 AM
thanks for reply
topology is something like this
P1 ------ PE1 ------- P2 ---- PE2
/ |
/ |
P3----PE3----PE4-------P4 ----- PE5
isis level-2 is configured
with fast reroute enabled in the whole ring
07-22-2013 07:32 AM
Ok in your topology IPFRR will partially work
Example let's say P3 is rotuing via P1 to reach PE2
In the case of P1-PE1 link faulre P1 can not use p3 as a loop free frr because igp still not converged and p3 still using p1 to reach pe2
What you can do is multi home PE3 and PE1 to both P1 and P3 to get around this limitation
Other option is if your network is mpls enabled you may read about remote LFA with LDP which can help you here
Hope this help
07-22-2013 10:18 AM
This is exactly the same problem i m facing
whenever P1--PE1 or PE1--P2 link goes down we have service impact
The multi-home solution is not practical right now
yes our network is MPLS enabled, but unfortunately i am not aware of remote LFA
how can I know more about this solution
Thanks again
07-22-2013 12:10 PM
Check out this link
http://www.cisco.com/en/US/docs/wireless/asr_901/Configuration/Guide/remote_lfa-frr.html
Hope this help, if helpful rate
07-22-2013 01:26 PM
again thank you ... i will read and try to look for solution
but i have some questions ...
why igp will not converge? is there any issue in is-is or is it the normal behaviour?
and why you said for this topology FRR will work partially; frankly how we can know this?
07-22-2013 10:25 PM
ok as per my example above
if P1 pre compute a back up path via P3 to reach PE2 prefixes and in a normal state P3 uses P1 to reach PE2 prefixes
then at the moment of failure if P1 uses P3 before ISIS converge P3 still uses P1 to reach these prefixes and this will form a loop
however if P1 uses P3 as a back path to reach P4-PE4 subnet then P1 can route via P3 as P3 dose not use P1 to reach this subbent and will not form a loop
hope this help
07-23-2013 12:28 PM
thank you very much yet again
It was really helpful ... will try to implement this in our network
07-31-2013 05:00 AM
as Marwan said 70 to 80% can be covered with LFA, i think redesign some metrice plus using Remote LFA (P1 to PE4)can raise your percentage up to ~90%.
however achiving more than 98% can be done only with the help of the TE tunnels.
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide