[Asterisk-Users] How do you handle NAT?

[C F]

Here is my experience in this area. Using asterisk on public IP no
nat, and no firewall. Polycom and Sipura clients inside NAT.
The sipura seems to be much more stable with almost everything, in
terms of asterisk being able to connect to it. I'm not using qualify
in sip.conf, but enabled them on the sipura.
The polycoms however is a different story. For some reason, the
polycoms allow asterisk to negotiate a new port so the port forwarding
rules don't really help much, even though I set the polycoms to have
different ports, and configured sip.conf with those ports. Because of
that (or so I think) they become unreachable every 2-3 minutes until
they reregister. Qualify (in sip.conf, since the polycoms don't have
such a setting) helps a lot, but doesn't get rid of the problem. I
even tried setting the register to 150 seconds but still it didn't
help. It's actually set to this in sip.conf:
maxexpirey=300
defaultexpirey=90
The main thing I'm trying to do now, that I think might help, is
getting asterisk to stick to the port number, and not renegotiate a
new port (the sipura works that way). Since I have port forwarding
rules on the setup port for each phone, I believe it will get rid of
most of the trouble.