[Serusers] Registrations behind NAT problem.

[Andrey Kuprianov]

 Hi,

Im facing some weird problem, when users register from behind NAT. Let
me try to break it down.

First of all, Im using ser 0.9.6 and my configuration file is almost
identical to that of mediaproxy+nat config file from getting started
bundle. I have asked my friends and colleagues to test my SIP-based
application behind NAT with their ADSL modems and strange thing
happens:

1. While one guy (say user1) has ADSL modem, which gives him address
of 192.168.0.3, he can register w/o problem. Contact header
<sip:user1 at 192.168.0.3:5060;transport=udp>;q=1.0

is sent in REGISTER request, and received back with 200 OK as

<sip:user1 at 192.168.0.3:5060;transport=udp>;q=1.0;expires=3600;received="sip:61.47.x.x:5060"
   (i have put "x" by myself)

2. Another guy (user2) has ADSL modem connected to a wireless access
point. The application sends in Contact:

<sip:surat at 10.0.0.12:5060;transport=udp>;q=1.0

but gets back in 200 OK (attention !!!):

<sip:surat at 124.120.x.x:41854;transport=udp>;q=1;expires=3600;received="sip:124.120.x.x:43041"

It gets Contact with a public IP back, which is not the case with
user1. How come?
I *wonder* why this is happening... Some kind of weird NAT?

I'd really appreciate if anyone can shed some light on this issue.

   Bests,

     Andrey.