[c-nsp] OSPF per-prefix LFA

[Adam Vitkovsky]

Hi Mohamad,

Just because it can be configured doesn't really mean the feature is supported and actually works in HW.
Since you did not see any difference in convergence times with or without the feature enabled it looks like it's actually not doing anything.
Changing the SPF timers did make a difference so it appears the HW can notify SW of the link failure promptly -so the problem doesn't appear to be there.

adam

From: Mohammad Khalil [mailto:eng_mssk at hotmail.com]
Sent: 02 June 2015 09:37
To: Adam Vitkovsky
Cc: cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] OSPF per-prefix LFA

Hi all
Thanks for the replies
Yes Adam it's supported , am using it on a virtual machine :)
I guess me using virtualized environment might caused the LFA not to work the way it should , but what am confused about now is to use LFA or to just manipulate the timers ?

Thanks again

BR,
Mohammad
________________________________
From: Adam.Vitkovsky at gamma.co.uk<mailto:Adam.Vitkovsky at gamma.co.uk>
To: eng_mssk at hotmail.com<mailto:eng_mssk at hotmail.com>
CC: cisco-nsp at puck.nether.net<mailto:cisco-nsp at puck.nether.net>
Subject: RE: [c-nsp] OSPF per-prefix LFA
Date: Thu, 28 May 2015 13:43:39 +0000

Hi Mohammad,

I have never had to tune IGP to get sub 50ms LFA failover times.
The failover times have nothing to do with IGP.
Actually the switchover itself (from primary to backup path) is done in couple of usec (microseconds).
So what you need to fight against is actually the time it takes the HW to realize there's no light on the link.
As it was suggested already tuning the "carrier-delay down" to 0 is an absolute must.

Yes tuning:
timers throttle lsa,
timers lsa arrival,
timers pacing flood
- is vital to propagate the information across the backbone as fast as possible so BGP can switch to backup NH ASAP if primary NH is unreachable.
But that's a different story altogether.

I think it's really hard to tell what's actually going on in virtual environments.
Looks like in your case LFA is really slow so SFP kicks in sooner than LFA that's why tuning SPF got you better results.
You might want to check how your virtual environment reports link failures (at what time intervals).
Is LFA actually supported on CSR?

adam

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