Subject: Re: [Sip] Max-Forward checking at UAS

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 05 Sep 2002 12:57:07 -0400

jumping in a bit late. Responses inline.

Christer Holmberg wrote:
> Hi,
> 
> I agree with you all that the cookie should not be used to determine if the
> sender does things according to RFC3261 or RFC2543. However, even if you
> say that "z9hG4bK" means that the branch-id is "safe" to use as transaction
> identifier, it indirectly does indicate if the sender does things according
> to RFC3261 or RFC2543, doesn't it? Anyway, there is no idea to argue about
> that :)

Absolutely not.

As Adam and Robert have pointed out, you cannot infer anything from the 
via cookie except that the branch ID is a transaction ID. 
Implementations aren't binary in terms of their support for 3261. Some 
support some of the features, others more, and others, all. Such mixed 
implementations are a reality, and that is why we choose to support 
backwards compatibility on a feature-by-feature basis rather than 
glomming it all into a new version of SIP.

> 
> I also agree with Robert that at least a UAS should not care about the
> value of the Max-Forwards header, since the message has reached its
> "destination". I guess another question is what proxies do when they
> receive a message without the header. A few options (all implementation
> specific, I think, so there is no idea to define any specific behaviour in
> the spec):

Well, I think I disagree with Robert on this one.

I would like Max-Forwards treatment at a server to be generic to all 
servers - proxies and UAS alike. If a proxy rejects a request with 
Max-Forwards: 0, so too should a UAS. However, the point is really one 
of philosophy; I can find no specific problem with a UAS ignoring 
Max-Forwards.

An interesting point of comparison, however, is the TTL header in the IP 
packet. Do hosts look at this field or not? I suspect they don't, which 
would probably support Robert's position....

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip