Subject: Re: [SIP] Max-Forwards + Proxies

From: Henning Schulzrinne <[email-masked]>
Date: Sat, 01 Jul 2000 14:15:53 -0400

Jonathan Rosenberg wrote:
> 
> Shail Bhatnagar wrote:
> >
> > I don't have a problem with this simplification - but the spec says
> > an incoming request with Max-Forwards of 0 MUST NOT be forwarded.
> > It does not say that the request cannot be locally processed and a
> > response returned. Since REGISTER (for the registrar) and CANCEL
> > will be absorbed by the proxy, I thought it is okay to process these
> > requests.
> > The relevant statement in the spec should be appropriately changed -
> >
> > request MUST NOT be forward and MUST NOT be processed.
> 
> That is the proposal; as I said, I think it is very confusing otherwise.
> 
> -Jonathan R.
> 

Just for reference: Here's the HTTP/1.1 behavior:

   Each proxy or gateway recipient of a TRACE or OPTIONS request
   containing a Max-Forwards header field MUST check and update its
   value prior to forwarding the request. If the received value is zero
   (0), the recipient MUST NOT forward the request; instead, it MUST
   respond as the final recipient. If the received Max-Forwards value is
   greater than zero, then the forwarded message MUST contain an updated
   Max-Forwards field with a value decremented by one (1).

   The Max-Forwards header field MAY be ignored for all other methods
   defined by this specification and for any extension methods for which
   it is not explicitly referred to as part of that method definition.

-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

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From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 05 Jul 2000 00:40:26 -0400

>    Max-Forwards field with a value decremented by one (1).

I don't have a major problem with this kind of behavior for OPTIONS (I
can still reject it with 483 and nothing very bad happens), but for
REGISTER this behavior is really bad.

So, the current proposal is that proxies don't forward requests with 0
Max-Forwards. If the request is OPTIONS, the entity responds as the
final recipient (noting that 483 is a valid response as the final
recipient). For all other methods, the final response MUST be 483 if
Max-Forwards is zero. 

Does that seem OK?

-Jonathan R.
-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
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