[Asterisk-Users] How do I diagnose the problem in this Asterisk test session with FWD?

[Luki]

> Call rejected: 503 Service Unavailable
The above is quite correct. You will notice that there is no answer
from FWD whatsoever to the NEW or REGREQ packets. Either your firewall
is blocking IAX traffic (incoming or outgoing), FWD's IAX is down or
unreachable from your location due to network trouble.

"iax2 show registry" probably shows "Request Sent". My suggestion, try
again later or use tcpdump to check for IAX traffic on your interface
(like "tcpdump -n src or dst port 4569").

--Luki