[Serusers] [Newbie question] - NAT/port messed up

[Andrei Pelinescu-Onciul]

On Nov 11, 2004 at 00:04, Thomas <thomasj at eworld.hu> wrote:
> 
> Hello!
> 
> I'm trying to make my 1st SIP-based system working. I use SER-0.8.14
> on Linux Sarge. I have usually UAs behind NAT firewalls.
> 
> I found a case, when UAs are working very oddly, I can't call from one
> of them, after sime time I can't reach one of them from outside, after
> some time when I call one UA, the 2nd is answering (and the same time
> when I call 2nd UA, the 2nd is answering).
> 
> I have 2 UAs [Grandstream BT100 & X-Lite v2.0] behind a linux NAT
> firewall. Both UAs use the same STUN and SER server.
> I did some tcpdumps and I found an interesting thing:
> 
> Internet Protocol, Src Addr: <FWPUBLICIP> (<FWPUBLICIP>), Dst Addr:  <SERIP> (<SERIP>)
> User Datagram Protocol, Src Port: 1024 (1024), Dst Port: 5060 (5060)
> Session Initiation Protocol
>     Request-Line: REGISTER sip:<MYDOMAIN> SIP/2.0
>         Method: REGISTER
>         Resent Packet: True
>         Suspected resend of frame: 31
>     Message Header
>         Via: SIP/2.0/UDP <FWPUBLICIP>;branch=z9hG4bK0dbeeb499dbd416e
[...]
> What is interesting is that REGISTER message went out from port 1024
> but 200 OK came to port 5060. Is this OK? I think here is some problem
> and this can make the phones working oddly.

If the phone wanted the answer on 1024, it should have advertised it in
the REGISTER's via. A least it should have added a rport parameter to
the Via.

You can try using force_rport() in ser config for all requests (or for
requests comming from this phone). This might break asymmetric UAs
though (not very common these days).


Andrei