asterisk users - Feb 2004 - Re: How to best debug SIP registration failure (Solved)

Thank you to Olle Johansson, Philipp von Klitzing, and others who 
suggested approaches to the problem.

To summarise what we did and how we ended up solving the problem:

Situation:
  1. Grandstream phone behind NAT box.
  2. Asterisk not behind NAT (with static IP).
  3. Phone cannot register.

Problem diagnosis:

1. Tested phone with FWD (http://www.pulver.com/fwd/) and was able to 
register and run echo test successfully. This indicates we have NAT 
configured properly and know enough about configuring the phone to have 
  some hope to get it working with Asterisk

2. Ran asterisk with verbose debuggery and "sip debug".

3. Ran tcpdump and tethereal to see what packets were arriving and 
departing the Asterisk server.

4. Ran netstat to verify that something was listening on the appropriate 
ports on the Asterisk box.

What we found:

(a) tcpdump and tethereal saw traffic from phone but nothing from Asterisk.

(b) "sip debug" reported nothing at all.

Putting all of the above together we were left with a number of 
hypothesises the most likely of which was that the registration packets 
(which we could see arriving on the net) were being blocked and not 
being seen by Asterisk.

Further research revealed that the system had iptables that were 
blocking the ports needed.

Once we reconfigured the iptables, things worked fine.

Sorry to have troubled the list and thank you for helping me towards 
discovering the solution (and providing valuable advice that will no 
doubt be invaluable in diagnosing future problems).

g.