[OpenSIPS-Users] Via header interpretation with rport parameter being set

[Iñaki Baz Castillo]

2009/9/14 Thomas Gelf <thomas at gelf.net>:
>> If a client uses symmetric SIP (as most of them do), and uses UDP,
>> then NAT is detected by comparing the real source IP:port with the
>> value of the Contact header.
>
> And that's exactly what I'm missing. As of
>
> http://www.opensips.org/html/docs/modules/devel/nat_traversal.html#id228455

Yes, I also miss it. In fact I use test function of nathelper module.


> there is no such test in OpenSIPS nat_traversal module. As you correctly
> pointed out, the whole rport-handling voodoo is not even needed - I'm
> already calling force_rport() for each request. I thought it might be
> even more elegant to care about what the client states - but you're
> absolutely right, that's a waste of ressources.

Note that if a client behind NAT doesn't use symmetric SIP, it will
NEVER receive replies (since it requires to receive replies in other
port, which is impossible from outside the router).


> As no test comparing the real source IP:port with the value in the
> Contact header is available, test 2 and 4 are still being used. However,
> they are either useless or could lead to wrong assumption (as in the
> example I mentioned).

You are right.


> So, to the long and the short of it, let's come back to my essential
> question (probably hidden between too much text in my former post):
>
> * would a new test checking whether Contact differs from the socket
>  where the UAC's packet came from make sense?

Sure! :)

Please report it in the tracker explaining what we have talked about
and I will give feedback to the report :)



-- 
Iñaki Baz Castillo
<ibc at aliax.net>