Re: [tsvwg] UDP-Options: UDP has two ”maximums”

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Fri, 02 April 2021 11:30 UTC

Return-Path: <gorry@erg.abdn.ac.uk>
X-Original-To: tsvwg@ietfa.amsl.com
Delivered-To: tsvwg@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 076F63A1071 for <tsvwg@ietfa.amsl.com>; Fri, 2 Apr 2021 04:30:04 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.901
X-Spam-Level:
X-Spam-Status: No, score=-1.901 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Pk6rXjIiwhT9 for <tsvwg@ietfa.amsl.com>; Fri, 2 Apr 2021 04:30:02 -0700 (PDT)
Received: from pegasus.erg.abdn.ac.uk (pegasus.erg.abdn.ac.uk [137.50.19.135]) by ietfa.amsl.com (Postfix) with ESMTP id 29EFD3A1072 for <tsvwg@ietf.org>; Fri, 2 Apr 2021 04:30:01 -0700 (PDT)
Received: from GF-MBP-2.lan (fgrpf.plus.com [212.159.18.54]) by pegasus.erg.abdn.ac.uk (Postfix) with ESMTPSA id 252291B001FE; Fri, 2 Apr 2021 12:29:56 +0100 (BST)
To: Joseph Touch <touch@strayalpha.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
References: <161366727749.10107.14514005068158901089@ietfa.amsl.com> <5f464f17-85ed-f105-35f9-02f35d04aed2@si6networks.com> <CALx6S364zGbq_HZNNVEaJHnHccuk4Zau2DXhmaVYbwnYQc-5bw@mail.gmail.com> <1847e8e3-543f-5deb-dd14-f7c7fa3677db@si6networks.com> <CALx6S34TPppMRJrOvyJ05LLeRvv+S51pQHJnzZDKk-qOdsF0AA@mail.gmail.com> <e41f3484-f816-e185-2d99-94323c8da732@si6networks.com> <CALx6S34qSxGijVcs229bAL5gMhMvMNYUXm3yEmrg6wxUiUAiaA@mail.gmail.com> <bf83d228-25bc-21bb-f984-d58ead6bf492@si6networks.com> <CALx6S35Kh-QAXJDAucuw5Wty37MBiwS=pqQknMZ+15b7D5Sn8A@mail.gmail.com> <34e78618-cb28-71a1-a9d3-7aec38032659@si6networks.com> <CAO42Z2zqD9_d2Fbr25Y2CV1GdzYKd167yf5DHeHna7V66pF65A@mail.gmail.com> <8296B6C0-0010-4EAE-A6C9-6C3D43AC5BAB@strayalpha.com> <28f28347-b6a8-9f38-e03c-70bf06322c48@erg.abdn.ac.uk> <93556D3A-3C42-4944-9202-DE75AE864CBA@strayalpha.com> <853caba2-b7ce-db2e-338c-ad1d161a5fe9@erg.abdn.ac.uk> <48DA3058-3380-46AC-951E-27B28489AAF6@strayalpha.com>
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
Message-ID: <846f084a-c441-1d2f-a858-e4d34d528c83@erg.abdn.ac.uk>
Date: Fri, 2 Apr 2021 12:29:55 +0100
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:78.0) Gecko/20100101 Thunderbird/78.9.0
MIME-Version: 1.0
In-Reply-To: <48DA3058-3380-46AC-951E-27B28489AAF6@strayalpha.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-GB
Archived-At: <https://mailarchive.ietf.org/arch/msg/tsvwg/hWD7zlRokr2RKgx6oY1Qo0my3sE>
Subject: Re: [tsvwg] =?utf-8?q?UDP-Options=3A_UDP_has_two_=E2=80=9Dmaximums?= =?utf-8?b?4oCd?=
X-BeenThere: tsvwg@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Transport Area Working Group <tsvwg.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tsvwg>, <mailto:tsvwg-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/tsvwg/>
List-Post: <mailto:tsvwg@ietf.org>
List-Help: <mailto:tsvwg-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tsvwg>, <mailto:tsvwg-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 02 Apr 2021 11:30:04 -0000

In the last IETF TSVWG meeting you asked for throughts about what MSS 
should mean?

I have now thought - the key unknown here is how large a datagram 
segment the remote receiver is willing to accept - i.e., what is the 
largest fragmented datagram I can send that would be reassembled. This 
might be any number, depending on the way in which the receiver is 
designed or configured. Whereas a sender could anticipate a common 
fragment size - e.g. 1200B, or use dplpmtud to discover this, there is 
no real way of determining the largest datagram that would be the option.

I think you suggested this as: Max reassembly size, a hard upper bound, 
similar to MSS_R.

Does this help?

Gorry