[c-nsp] ECMP failing over time?

[Chris Evans]

I beleive what you guys are referring to is cef polarization..   we
implement extra commands at every other tier to fight this..  I just can't
remember them right now lol.
On Oct 3, 2010 3:47 AM, "Reinhold Fischer" <reinhold.fischer at gmx.net> wrote:
> 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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