Re: p1: Via and gateways

Mark Nottingham <mnot@mnot.net> Wed, 08 May 2013 02:17 UTC

Return-Path: <ietf-http-wg-request@listhub.w3.org>
X-Original-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Delivered-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 6265421F8C23 for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Tue, 7 May 2013 19:17:47 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -10.58
X-Spam-Level:
X-Spam-Status: No, score=-10.58 tagged_above=-999 required=5 tests=[AWL=0.019, BAYES_00=-2.599, RCVD_IN_DNSWL_HI=-8]
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 YEj2pJSg4CWO for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Tue, 7 May 2013 19:17:41 -0700 (PDT)
Received: from frink.w3.org (frink.w3.org [128.30.52.56]) by ietfa.amsl.com (Postfix) with ESMTP id 7207421F8C33 for <httpbisa-archive-bis2Juki@lists.ietf.org>; Tue, 7 May 2013 19:17:41 -0700 (PDT)
Received: from lists by frink.w3.org with local (Exim 4.72) (envelope-from <ietf-http-wg-request@listhub.w3.org>) id 1UZtvW-0000NR-Pt for ietf-http-wg-dist@listhub.w3.org; Wed, 08 May 2013 02:16:18 +0000
Resent-Date: Wed, 08 May 2013 02:16:18 +0000
Resent-Message-Id: <E1UZtvW-0000NR-Pt@frink.w3.org>
Received: from lisa.w3.org ([128.30.52.41]) by frink.w3.org with esmtp (Exim 4.72) (envelope-from <mnot@mnot.net>) id 1UZtvK-0000Jx-JU for ietf-http-wg@listhub.w3.org; Wed, 08 May 2013 02:16:06 +0000
Received: from mxout-07.mxes.net ([216.86.168.182]) by lisa.w3.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from <mnot@mnot.net>) id 1UZtvI-0002TI-MZ for ietf-http-wg@w3.org; Wed, 08 May 2013 02:16:06 +0000
Received: from [192.168.1.80] (unknown [118.209.105.214]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by smtp.mxes.net (Postfix) with ESMTPSA id 58BB122E253; Tue, 7 May 2013 22:15:41 -0400 (EDT)
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 6.3 \(1503\))
From: Mark Nottingham <mnot@mnot.net>
In-Reply-To: <20130424063810.GG15918@1wt.eu>
Date: Wed, 8 May 2013 12:15:37 +1000
Cc: Amos Jeffries <squid3@treenet.co.nz>, ietf-http-wg@w3.org
Content-Transfer-Encoding: quoted-printable
Message-Id: <185F20CA-EA93-4E8F-BB9A-C10A5FAC7C31@mnot.net>
References: <F7810D5C-45A6-4D01-83ED-2A9AB5856813@mnot.net> <alpine.LRH.2.01.1304200017490.18732@egate.xpasc.com> <37AD85F8-D0E1-4B9D-9BF0-99EBE83ADF8D@mnot.net> <20130420080919.GP26517@1wt.eu> <51733C74.9050701@treenet.co.nz> <20130423064325.GC8496@1wt.eu> <74FF747A-D93A-436D-ACFB-F72BFFBBA2A4@mnot.net> <20130424063810.GG15918@1wt.eu>
To: Willy Tarreau <w@1wt.eu>
X-Mailer: Apple Mail (2.1503)
Received-SPF: pass client-ip=216.86.168.182; envelope-from=mnot@mnot.net; helo=mxout-07.mxes.net
X-W3C-Hub-Spam-Status: No, score=-3.4
X-W3C-Hub-Spam-Report: AWL=-3.350, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001
X-W3C-Scan-Sig: lisa.w3.org 1UZtvI-0002TI-MZ 0396c85588a6b0c68b8c801d0cba1c84
X-Original-To: ietf-http-wg@w3.org
Subject: Re: p1: Via and gateways
Archived-At: <http://www.w3.org/mid/185F20CA-EA93-4E8F-BB9A-C10A5FAC7C31@mnot.net>
Resent-From: ietf-http-wg@w3.org
X-Mailing-List: <ietf-http-wg@w3.org> archive/latest/17885
X-Loop: ietf-http-wg@w3.org
Resent-Sender: ietf-http-wg-request@w3.org
Precedence: list
List-Id: <ietf-http-wg.w3.org>
List-Help: <http://www.w3.org/Mail/>
List-Post: <mailto:ietf-http-wg@w3.org>
List-Unsubscribe: <mailto:ietf-http-wg-request@w3.org?subject=unsubscribe>

OK, it seems like we agree we can relax the MUST generate Via on responses from gateways, provided that they don't removing any existing Via header. 

I'll mark this for -23.


On 24/04/2013, at 4:38 PM, Willy Tarreau <w@1wt.eu> wrote:

> On Wed, Apr 24, 2013 at 01:27:45PM +1000, Mark Nottingham wrote:
>> 
>> On 23/04/2013, at 4:43 PM, Willy Tarreau <w@1wt.eu> wrote:
>> 
>>> Then I would propose this addition :
>>> 
>>>  Multiple Via field values represent each proxy or gateway that has
>>>  forwarded the message.  Each recipient MUST append its information
>>>  such that the end result is ordered according to the sequence of
>>> -  forwarding applications.
>>> +  forwarding applications. A gateway MAY simply relay any existing Via
>>> +  header field if it does not change the HTTP version, but it MUST NOT
>>> +  remove it.
>> 
>> This is already covered further down:
>> 
>>> A proxy or gateway may combine an ordered subsequence of Via header field
>>> entries into a single such entry if the entries have identical
>>> received-protocol values.
> 
> I don't read it exactly the same way, but probably it achieves the same in
> the end.
> 
>> The question I was raising was specific: can we relax the requirement for a
>> gateway to add Via to responses if there isn't already one present?
> 
> I think yes, we can relax it, as if there was none, then it means the
> gateway has not changed the connection's behaviour and the next hop just
> assumes the connection comes from the client. Again, in my understanding,
> Via is used to understand what transformation was operated on the path
> and what capabilities are offered. If the gateway does not change anything,
> Via offers no value except detecting loops. And since most gateways simply
> forward to the configured next hop, the risk of loop is not caused by
> external environment (eg: DNS) but by the configuration so it's not a
> problem.
> 
> But if we do so, we must specify that a gateway MUST NOT remove the
> Via header field in any case, otherwise it will break the loop detection
> mechanism of some other components.
> 
> Regards,
> Willy
> 

--
Mark Nottingham   http://www.mnot.net/