Subject: [Sip] draft-rosenberg-sip-outbound-discovery-mid-dialog - dhcp overide or not?

From: Cullen Jennings <[email-masked]>
Date: Fri, 3 Nov 2006 18:25:35 -0800

There is an issues about using outbound proxies discovered thought  
DHCP where it is not clear to me what we want the solution to be.  
Once we are clear on the desired behavior it is trivial to get the  
draft to provide that. Let me try to describe the problem...

If a phone has no configuration, no proxies, no aor etc and it gets  
connected to the networks and finds out a proxy name via DHCP and  
uses that to make outbound calls, I have no problem that is great.  
The question is what happens with a phone that is configured, has a  
AOR, credentials, etc.

One view is that if DHCP returns a result, you use that as the  
outbound. The argument will be made that this is the way you discover  
the proxy in the hotel that lets you traverse the firewall. But  
consider the security implications of this. It means that anyone that  
spoof a DHCP response at a wireless hot spot can force you to connect  
to them. Even if you are doing SIPS, you will pass all your signaling  
through the attackers proxy and they will be able to see it all.

Perhaps there is a part of this that I am missing but the more I  
think about it, it does not seem like you want to actually use  
outbound proxies that were discovered via DHCP.

(Note this has nothing to do with a home proxy telling you to use a  
proxy in a visited network - here someone you trust, the home proxy,  
told you to trust the proxy in the visited network)

--------

One other trivial note - when talking about the names in the  
certificates, I think the text needs to be updated a bit to cover  
certificates that have more than one name in them

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