[SR-Users] OT: are there still asymmetric SIP clients?

[Iñaki Baz Castillo]

2011/6/22 Klaus Darilion <klaus.mailinglists at pernau.at>:
> Just a small survey: Are you still using NAT detection checks? I prefer
> to apply NAT traversal always (never trust the contact header) which of
> course only works if all the clients are symmetric.

I would like to tell a recent issue I've suffered in my company:

- Kamailio with public IP and optional rtpproxy server.
- Two users behind same NAT.
- Both users use STUN so announce public IP:ports in headers and SDP.
- User A calls to B.
- Kamailio does not detect NAT (due to STUN) so doesn't apply
rtpproxy, neither when routes the call to user B.
- So user A sends RTP to the public IP of its NAT router, same as user B.
- In some routers this work, but in this case it does not properly
perform NAT port forwarding and there is no audio.

Solutions:
1) Remove STUN from clients (not always feasible).
2) Always use RtpProxy. Easier.



> Thus - do you still see asymmetric SIP clients?

Yes, I've seen some Alcatel OXO using asymmetric SIP. A pain if you do
"force_rport".

Solution:
- Just perform "force_rport" if the client is detected as behind NAT
(note that assymetric SIP clients can ***NEVER*** run behind NAT).


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