Subject: [Simple] simple-im-01 Section 7 Proxy processing

From: "Rawlins, Diana" <[email-masked]>
Date: Wed, 01 Aug 2001 01:14:34 +0000

Section 7.4 states that proxies must not insert
record-route headers. Couldn't this record-route
restriction could interfere with some firewall 
/ NAT traversal schemes ? It seems too limiting.

Also, why is there the limitation that if the 
proxy is not the home domain (registration),
that a 404 is returned (rather than forwarding
on the MESSAGE) ?

-Diana

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From: Ben Campbell <[email-masked]>
Date: Sun, 05 Aug 2001 11:53:47 -0500

> / NAT traversal schemes ? It seems too limiting.

The point behind this is that a MESSAGE request, in itself, implies no 
concept of a session or call leg. There is nothing to record-route. This 
is like REGISTER, where each request stands alone. If a proxy _did_ 
insert a record-route header, the UAC would have nothing to do, as there 
are no further requests associated with the original MESSAGE for it to 
insert a Route header into.

> that a 404 is returned (rather than forwarding

In this case, we are talking about proxies that use REGISTER messages to 
set up routing. The text could be a little clearer, in that we are 
talking about proxies that _only_ route via REGISTERS. For example, if 
the proxy example.com receives a MESSAGE request for 
sip:[email-masked], but the proxy (or the registrar it uses) has no 
registration for sip:[email-masked], it returns a 404.

I more clear way of stating this would be if a proxy receives a MESSAGE 
request where the domain part of the request-URI refers to itself, and 
the user part of the request-URI refers to a user that the proxy has no 
knowledge of, then it should return a 404. This should not be confused 
with the situation where a proxy receives a request and the _domain_ 
part of the request-uri does not refer to itself. In that case, it 
should forward the request to the domain in the request-URI.