IETF Logo Mail Archive

Re: [tcpm] Exceeding value in MSS option?

Joseph Touch <touch@strayalpha.com> Tue, 20 October 2020 21:18 UTC

Return-Path: <touch@strayalpha.com>
X-Original-To: tcpm@ietfa.amsl.com
Delivered-To: tcpm@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 6A3F53A13B2 for <tcpm@ietfa.amsl.com>; Tue, 20 Oct 2020 14:18:36 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.319
X-Spam-Level:
X-Spam-Status: No, score=-1.319 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_NEUTRAL=0.779, URIBL_BLOCKED=0.001] autolearn=no autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=strayalpha.com
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 LlywC9XoNqLc for <tcpm@ietfa.amsl.com>; Tue, 20 Oct 2020 14:18:34 -0700 (PDT)
Received: from server217-4.web-hosting.com (server217-4.web-hosting.com [198.54.116.98]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 2992D3A13AD for <tcpm@ietf.org>; Tue, 20 Oct 2020 14:18:30 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=strayalpha.com; s=default; h=To:References:Message-Id: Content-Transfer-Encoding:Cc:Date:In-Reply-To:From:Subject:Mime-Version: Content-Type:Sender:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=34wfrVoMLEAYjgxns85/G/EkymsqgY8sb6uW26pesrA=; b=boIQQYyPkQ2Bq5mhc8T2tyNNN zEp0I1vDtSY18+YJf9f6uUcRu5lyY5akO7cNR8oZnJ1xBFWUb8HL1I0xNphWSYWXM59/NCon4159U h7ch1GvuT3wAwIyaxkQHNCpgbewhOYHJj25ER7v5bZLjIa+owOsOxafnuxiNcf9MGEDFtvdlTPc13 OWtC1qh6IIudJ6hNXdWBV1UWOCNDwSAHKeGLW7rUauUFAtnuAvNJsQQwZ35ovEWhPlhLKkD5sEeN4 S179x4AiVt0nkgKW3EP9X1eMsmdhJSAzaBi9ULL71zKdIgFs7UllmYAzzkUYZTeu+MfaR/bDYKWkn vR01K1S6g==;
Received: from cpe-172-250-225-198.socal.res.rr.com ([172.250.225.198]:60722 helo=[192.168.1.14]) by server217.web-hosting.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from <touch@strayalpha.com>) id 1kUz1S-003Yqh-UM; Tue, 20 Oct 2020 17:18:27 -0400
Content-Type: text/plain; charset="utf-8"
Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.1\))
From: Joseph Touch <touch@strayalpha.com>
In-Reply-To: <6AEBE48D-11BC-4837-BDB1-13E93CE11C84@lurchi.franken.de>
Date: Tue, 20 Oct 2020 14:18:22 -0700
Cc: "Scharf, Michael" <Michael.Scharf@hs-esslingen.de>, "tcpm@ietf.org Extensions" <tcpm@ietf.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <B8CD4F13-A722-4894-AD5F-20EFE3BC55EC@strayalpha.com>
References: <CAM4esxQzydPBTjVQvtp3766mCH5L65LdRSkFzQkdeKgUfhKacA@mail.gmail.com> <78558F1C-9194-4797-BE22-E553E1412E46@lurchi.franken.de> <7ded391321f94d0fb90fb5296de9fe43@hs-esslingen.de> <6AEBE48D-11BC-4837-BDB1-13E93CE11C84@lurchi.franken.de>
To: Michael Tuexen <michael.tuexen@lurchi.franken.de>
X-Mailer: Apple Mail (2.3608.120.23.2.1)
X-OutGoing-Spam-Status: No, score=-1.0
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname - server217.web-hosting.com
X-AntiAbuse: Original Domain - ietf.org
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain - strayalpha.com
X-Get-Message-Sender-Via: server217.web-hosting.com: authenticated_id: touch@strayalpha.com
X-Authenticated-Sender: server217.web-hosting.com: touch@strayalpha.com
X-Source:
X-Source-Args:
X-Source-Dir:
X-From-Rewrite: unmodified, already matched
Archived-At: <https://mailarchive.ietf.org/arch/msg/tcpm/fvxH5ZiSkOyJ7I-ZID8J9OCLUsU>
Subject: Re: [tcpm] Exceeding value in MSS option?
X-BeenThere: tcpm@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: TCP Maintenance and Minor Extensions Working Group <tcpm.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tcpm>, <mailto:tcpm-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/tcpm/>
List-Post: <mailto:tcpm@ietf.org>
List-Help: <mailto:tcpm-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tcpm>, <mailto:tcpm-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 20 Oct 2020 21:18:36 -0000


> On Oct 20, 2020, at 2:04 PM, Michael Tuexen <michael.tuexen@lurchi.franken.de> wrote:
> 
>> On 20. Oct 2020, at 21:56, Scharf, Michael <Michael.Scharf@hs-esslingen.de> wrote:
>> 
>> ...
>> I am not sure if we should simply remove the whole paragraph, including e.g. the reference to RFC 6691. Readers
> The paragraph starts with:
> 
> In order to accommodate unrequested TCP options that may be used by
> some TCP implementations, a constrained device may advertise an MSS
> smaller than 1220 bytes (e.g. not larger than 1200 bytes).

What does “unrequested” mean? It legitimately means options users haven’t asked for but are enabled somehow (default, OS override, etc.).

But that’s already taken care of - the side sending MMS indicates the value without considering options *because* it is the other side that uses the MSS *and its knowledge of which options it is adding, both at IP and TCP* to determine how much data payload room is available.

(And no, I still don’t think this should include a guess as to “how much a middlebox will expand the packet”).

> I don't think the selection of the MSS should depend on TCP options.

RFC6691 is very clear - it definitely should not.

> A TCP stack may send an MSS option with a value lower then 1220, but
> it should not do it due to any TCP options.

Agreed.

Joe

v2.23.0 | Report a Bug | By Email