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Re: [v6ops] PMTUD issue discussion

joel jaeggli <joelja@bogus.com> Fri, 05 September 2014 00:52 UTC

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Date: Thu, 04 Sep 2014 17:52:35 -0700
From: joel jaeggli <joelja@bogus.com>
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To: Brian E Carpenter <brian.e.carpenter@gmail.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> <5408FD25.4000505@gmail.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 9/4/14 5:00 PM, Brian E Carpenter wrote:
> 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.

sure that's kinda I find it necessary make sure the packet makes it when
i get one. I suspect even 1220 can hose you in some corner case... I'd
rather have my extra 220 bytes of pdu in any event.

>    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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