Subject: Re: [MMUSIC] ICE Question: Sharing the same IP between two UAs on different networks

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 01 Aug 2007 09:47:40 -0400

Take a look at appendix B.4 of ICE, which discusses this case and how 
ICE addresses it.

Some specific answers below:

Diego B wrote:
> Hi;
> I apologies if this question is out of scope or
> not relevant.
> 
> After the tutorial I was thinking about the case
> where UA1 and UA2 share the same private IP but in different networks.
> lets say UA1 in acme.com and UA2 in foo.com.
> What will be the situation here ?
> UA1 and UA2 will send media to their own IP ? or
> ICE will recognize the problem in one of the protocol steps ?
> or may be this situation can not happen at all.

The check will occur, but because the short-term credential is wrong, it 
will immediately fail.

> 
> Another similar question is if
> UA1 and UA2 are in the same network
> and UA3 in a different network but with the same private IP range.

Same as above. Dealing with these cases is one of the reasons that the 
short term credential is formed by combining username fragments from 
both sides.

> 
> UA1 has the same IP than UA3.
> UA2 makes a call to UA3.
> In the UA3's SDP UA2 will see the private IP of UA3 that is the same as 
> UA1,
> so if UA2 proves that IP there can be a chance that UA1 answers to UA2 
> requests.

No, since it will not know the username fragment, it will not be able to 
authenticate the STUN response. So, the check from UA2 to UA1 will fail. 
However, checks along a different path (through server reflexive or 
relayed candidates) will succeed since those are properly routed to UA3.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Cisco Fellow                                   Parsippany, NJ 07054-2711
Cisco Systems
[email-masked]                              FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
http://www.cisco.com

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