[c-nsp] ECMP failing over time?

[Reinhold Fischer]

Is "ip multicast multipath" enabled? Take care of the usage guidlines
and limitations before enabling it ...

hth
Reinhold

On Sun, Oct 3, 2010 at 7:10 AM, John Neiberger <jneiberger at gmail.com> wrote:
> This is entirely multicast. We used the s-g-hash to lock each S,G to a
> link, but we didn't think it through. We really should have started
> out using the next-hop-based hash so that the same S,G can be served
> by any link in the group. With s-g-hash, it always gets locked to the
> same bundle.
>
> However, I just thought of another potential culprit. I'm going to
> have to think it through, though.
>
> On Sat, Oct 2, 2010 at 10:17 PM, Keegan Holley
> <keegan.holley at sungard.com> wrote:
>> 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
>>> >
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>>
>>
>
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