Re: [v6ops] PMTUD issue discussion

Brian E Carpenter <brian.e.carpenter@gmail.com> Fri, 05 September 2014 00:00 UTC

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Date: Fri, 05 Sep 2014 12:00:37 +1200
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: joel jaeggli <joelja@bogus.com>
References: <0D370E74-688B-4EB3-A691-309A03AF20BA@cisco.com> <53FBA174.2040302@isi.edu> <53FBA6E1.90905@bogus.com> <CAPi140PMeM9omtm11+NHa2ywUfof_tE7HknKExtoEb32mm7L_w@mail.gmail.com> <71D0D5E8-80E9-430B-8ED4-16C1F99082CC@cisco.com> <54020ECC.4000000@globis.net> <CAEmG1=redpYUnv9R-uf+cJ4e+iPCf6zMHzVxeKNMGjcC=BjR+Q@mail.gmail.com> <5402C26A.8060304@globis.net> <540626F6.1020103@scea.com> <28F170C9-1E44-42CB-B11A-4A7173511D22@puck.nether.net> <5408F5DB.6000906@bogus.com>
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Cc: v6ops@ietf.org, Tom Perrine <tperrine@scea.com>
Subject: Re: [v6ops] PMTUD issue discussion
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On 05/09/2014 11:29, joel jaeggli wrote:
> On 9/4/14 3:09 PM, Jared Mauch wrote:
>> We configure customer links at 1500 (default), 4470 and 9000.
> 
> in the cases that I experienced I have my mss set to 1440. So clients
> with a higher MTU than 1500 are no so much of an issue. almost all of
> the cases that I have have examined were due to encapsulation.

Yes, and MSS negotiation down to 1220 doesn't always work, so
with 1280 tunnels still around, even 1440 can cause failures.

   Brian

> 
>> - Jared
>>
>>> On Sep 2, 2014, at 4:22 PM, Tom Perrine <tperrine@scea.com> wrote:
>>>
>>> What MTUs are actually (commonly) seen in the wild?
>>>
>>> I can only think of less than a dozen that I would expect to see, assuming that the actual MTU is based solely on the underlying network technology.
>>>
>>> Is planning and assuming that we'll see each and every possible MTU actually necessary?
>>>
>>> I agree that we wouldn't want to artificially limit MTUs to only a few common ones, I mean look how /64s became embedded in silicon...
>>>
>>>
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