[Asterisk-Users] SIP/NAT disconnection issue

[Scott Bussinger]

Help! I'm having an odd problem that I'm not seeing in any of the list 
archives and thought I'd ask and see if anyone can help.

I've got Asterisk behind a NAT and an SPA-841 SIP phone behind a different 
NAT. Everything works fine (incoming calls ring, outgoing calls work, audio 
in both directions, etc.) except for one thing -- when I hangup the SIP 
phone, Asterisk never disconnects the call. I've hooked up a syslog server 
and it appears the phone is sending a BYE command. However, running with SIP 
DEBUG on the server shows no SIP activity when the disconnect occurs. 
There's no indication on the firewall log that any packets were blocked for 
any reason (it's a separate linux box serving as a firewall/router).

Presumably I've got a NAT issue of some sort that's causing my problem --  
can anyone suggest any possibilities as to what's wrong and what I might do 
to solve it?