[Kamailio-Users] two UACs behind same NAT

[Dubravko Caric]

Hi,



----- Original Message ----
From: Iñaki Baz Castillo <ibc at aliax.net>
Cc: users at lists.kamailio.org
Sent: Monday, May 4, 2009 5:07:38 PM
Subject: Re: [Kamailio-Users] two UACs behind same NAT


> There is a really easy way to detect if a router is performing SIP ALG:
> - Configure you UA in the LAN with *no* STUN/ICE, just private IP.
> - Capture a INVITE/REGISTER from that UA in the proxy (in the public network).
> - Check if "Via" and/or "Contact" headers contain the router public IP
> instead of the UA private IP.
> - If so, you are behind a *fucking* router with SIP ALG enabled.

I did everything as you described and I can confirm that this router has SIP ALG enabled. 


> If you can dissable it (by web, telnet...) please add that information
> to the wiki page:
>  http://www.voip-info.org/wiki/view/Routers+SIP+ALG
> (or sent it to me directly and I'll add it).

there is no way to change this (turn ON/OFF) because there is no such option in the web interface of the router. what i will try to do (over this weekend) is to load DD-WRT firmware (which isn't Linksys firmware) and if this goes well I'll put this solution on wiki.


>>>How is possible that the proxy replaces 31479 with 0 ???
>>>You must be doing something wrong with the Contact header.
>>
>> i'm
>> not doing any manipulation with Contact header, all other scenarios are
>> working fine as long as I don't use two clients behind this specific
>> router.

> Let me understand:
> 
> - UA1 sends "200 OK" and when you capture it in the proxy it has port
> 31479 in Contact header, is it?
> - When this "200 OK" leaves the proxy it has 0 in Contact header, is it?

I checked this closely once more and I was wrong (I had too much traces open) :( what really happens is that UAC sends "OK" with right port in Contact header towards the router but the router is the one that changes this port to "0" and sends this malformed message to the proxy.


Thanks once more

Dubravko