[c-nsp] OSPF per-prefix LFA

Mohammad Khalil eng_mssk at hotmail.com
Tue Jun 2 06:26:26 EDT 2015

Got your point :)
regarding tunning , is there a was to judge the values that should be in place with affecting performance ?

From: ggiannou at gmail.com
Date: Tue, 2 Jun 2015 12:54:42 +0300
Subject: Re: [c-nsp] OSPF per-prefix LFA
To: eng_mssk at hotmail.com
CC: adam.vitkovsky at gamma.co.uk; cisco-nsp at puck.nether.net

Hi Mohammad, 
It's not one or the other..With OSPF tuning you improve convergence for sure and as others said, it's a good practice to do so.If you also implement LFA, you have an extra bonus in convergence time.
On Tue, Jun 2, 2015 at 11:36 AM, Mohammad Khalil <eng_mssk at hotmail.com> wrote:
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



From: Adam.Vitkovsky at gamma.co.uk

To: eng_mssk at hotmail.com

CC: 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?


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