[c-nsp] ECMP failing over time?

[Chris Evans]

http://m.mcisco.com/pocket.paper?url2=http%3a%2f%2fwww.cisco.com%2fen%2fUS%2fdocs%2fsolutions%2fEnterprise%2fCampus%2fHA_campus_DG%2fhacampusdg.pdf

I'm doing this from my phone so I am not sure how that url comes through.
On Oct 3, 2010 7:55 AM, "Chris Evans" <chrisccnpspam2 at gmail.com> wrote:
> 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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>>
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