[c-nsp] ECMP failing over time?

[Keegan Holley]

I've seen similar effects.  I'm not sure there's a method to evenly
distribute traffic for an indefinite period.  I'm also not sure what you're
routing, but the problems I've seen are usually caused by the fact that each
flow/hash result differs in size and duration.  Adding extra variables to
the equation always helps, but it's almost impossible to keep an even
spread.  I suppose your current goal is to simply stop the outages though.


On Sat, Oct 2, 2010 at 7:17 PM, John Neiberger <jneiberger at gmail.com> wrote:

> I hate to answer my own question, but I think I figured it out. We're
> using s-g-hash basic, which is prone to polarization. I think that's
> what we're seeing. Our traffic has become polarized and has developed
> an affinity for a subset of links in our "bundles". I'm recommending
> that we switch to s-g-hash next-hop-based to see if that resolves the
> problem.
>
> On Sat, Oct 2, 2010 at 2:18 PM, John Neiberger <jneiberger at gmail.com>
> wrote:
> > We converted several connections last week from Etherchannels to
> > routed links with ECMP. We verified that traffic was load-sharing over
> > those links after making the change. Now, a week later, we are seeing
> > instances where traffic is preferring one or two links out of each
> > "bundle". In some cases all the traffic is flowing over a single link
> > in a four-link setup. This is overloading those connections and we
> > can't figure out why. We are using s-g-hash basic. Should we switch to
> > s-g-hash next-hop-based?
> >
> > This is causing production issues right now, so I've opened up a TAC
> > case, but I thought I'd ask here, as well, just in case someone had
> > seen this before.
> >
> > Thanks,
> > John
> >
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>
>
>