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Re: p1: Via and gateways

From: Mark Nottingham <mnot@mnot.net>
Date: Wed, 8 May 2013 12:15:37 +1000
Cc: Amos Jeffries <squid3@treenet.co.nz>, ietf-http-wg@w3.org
Message-Id: <185F20CA-EA93-4E8F-BB9A-C10A5FAC7C31@mnot.net>
To: Willy Tarreau <w@1wt.eu>
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/
Received on Wednesday, 8 May 2013 02:16:06 UTC

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