[Kamailio-Users] two UACs behind same NAT

[Iñaki Baz Castillo]

2009/5/4 Dubravko Caric <dubravko_caric at yahoo.com>:
>>Questions:
>>- Does this router use the painful SIP ALG?
>>     http://www.voip-info.org/wiki/view/Routers+SIP+ALG
>
> didn't find anything regarding SIP and ALG in the device specification but I did find this http://www.easyofficephone.com/support/router-compatibility#linksys_wrt54g:
>
> "This router is not recommended for use with voice over ip services
> using the stock firmware from Linksys. This model router is known to
> damage and modify SIP packets in such a way that it prevents voice over
> ip packets from being formatted correctly and can cause a multitude of
> problems."
>
> i'll check everything once more...

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.

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).


>>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?




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