IETF Logo Mail Archive

Re: [v6ops] proposed TCP MSS text for rfc6204bis

Warren Kumari <warren@kumari.net> Mon, 21 May 2012 14:49 UTC

Return-Path: <warren@kumari.net>
X-Original-To: v6ops@ietfa.amsl.com
Delivered-To: v6ops@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 9D2C921F84FA for <v6ops@ietfa.amsl.com>; Mon, 21 May 2012 07:49:05 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -105.999
X-Spam-Level:
X-Spam-Status: No, score=-105.999 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, J_CHICKENPOX_13=0.6, RCVD_IN_DNSWL_MED=-4, USER_IN_WHITELIST=-100]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id tQ1hvnTNKIr4 for <v6ops@ietfa.amsl.com>; Mon, 21 May 2012 07:49:05 -0700 (PDT)
Received: from vimes.kumari.net (vimes.kumari.net [198.186.192.250]) by ietfa.amsl.com (Postfix) with ESMTP id 197ED21F84D8 for <v6ops@ietf.org>; Mon, 21 May 2012 07:49:05 -0700 (PDT)
Received: from dhcp-172-19-118-235.cbf.corp.google.com (unknown [64.13.52.115]) by vimes.kumari.net (Postfix) with ESMTPSA id 625D11B402F8; Mon, 21 May 2012 10:49:04 -0400 (EDT)
Mime-Version: 1.0 (Apple Message framework v1278)
Content-Type: text/plain; charset="windows-1252"
From: Warren Kumari <warren@kumari.net>
In-Reply-To: <20120520140421.9E5A520C611B@drugs.dv.isc.org>
Date: Mon, 21 May 2012 10:49:02 -0400
Content-Transfer-Encoding: quoted-printable
Message-Id: <96B542C8-F19D-470D-B648-154946D791A6@kumari.net>
References: <4FB74456.2090009@gmail.com> <20120519080006.GZ84425@Space.Net> <4FB775A3.1030900@gmail.com> <20120519.141906.74656347.sthaug@nethelp.no> <4FB7A7CC.6060503@gmail.com> <m27gw7eub0.wl%randy@psg.com> <4FB89733.2080106@gmail.com> <20120520140421.9E5A520C611B@drugs.dv.isc.org>
To: Mark Andrews <marka@isc.org>
X-Mailer: Apple Mail (2.1278)
Cc: v6ops@ietf.org
Subject: Re: [v6ops] proposed TCP MSS text for rfc6204bis
X-BeenThere: v6ops@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: v6ops discussion list <v6ops.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/v6ops>, <mailto:v6ops-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/v6ops>
List-Post: <mailto:v6ops@ietf.org>
List-Help: <mailto:v6ops-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/v6ops>, <mailto:v6ops-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 21 May 2012 14:49:05 -0000

[ Top posting / meta questions ]

So, both my memory and my google-foo are failing me…

Can anyone remember *why* the v6 in MTU is 1280 (and please don't say "Because the RFC says so!"…)

I have some niggling voice in the back of my head making 3GPP noises, but…

W

On May 20, 2012, at 10:04 AM, Mark Andrews wrote:

> 
> In message <4FB89733.2080106@gmail.com>, Brian E Carpenter writes:
>> On 2012-05-19 22:26, Randy Bush wrote:
>>>> If you want to send packets of arbitrary size, in any environment
>>>> where PMTUD is impossible or fails, won't you need to always include
>>>> a fragmentation header in every packet greater than 1280?
>>> 
>>> see discussion of jumbo frames, commonly 4k or 9k, between consenting
>>> adults on known links
>> 
>> Yes indeed, but that isn't the general case. Across the open Internet,
>> I think we have the situation I described.
>> 
>> On 2012-05-19 21:16, Gert Doering wrote:
>> 
>>>>> UDP packets larger than 1280 bytes
>>>>> Don't do that!
>>> 
>>> Tell that to the DNS people.  They seem to really like not-using-TCP.
>> 
>> Yes, but I understand that DNSSEC more or less dooms that plan anyway.
>> 
>> However, I thinks it's true that the only fail-safe solution is to
>> include a frag header if you need to send UDP >1280.
>> 
>>   Brian
> 
> For DNS we just fragment at 1280 using IPV6_USE_MIN_MTU.   We were
> thinking about this back in 1998 (draft-ietf-ipngwg-bsd-frag-00.txt)
> which was rolled into the advanced socket api.  It took a few more
> years than I would have liked to become RFC and for implementations
> to be available.  EDNS was already being developed back then and
> it was obvious that PMTUD wouldn't work for large nameservers even
> if they got the ICMPv6 PTBs.
> 
> For DNS there is little to be gained by trying to send any bigger
> packets.
> 
> YMMV for other UDP based protocols.
> 
> Mark
> 
>>    Brian
>> _______________________________________________
>> v6ops mailing list
>> v6ops@ietf.org
>> https://www.ietf.org/mailman/listinfo/v6ops
> -- 
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                 INTERNET: marka@isc.org
> _______________________________________________
> v6ops mailing list
> v6ops@ietf.org
> https://www.ietf.org/mailman/listinfo/v6ops
> 

-- 
With Feudalism, it's your Count that votes.

v2.23.0 | Report a Bug | By Email