[asterisk-users] sip forward behind a nat

[nik600]

Hi

i have to forward a call from my asterisk server on another server but
my server is behind nat.

How can i setup my extension.conf?

Actually i have set up it as follows:

exten => 0465666666,1,Dial(SIP/user at dormain)

my server has a private ip 192.168.100.249 and doesn't have a public ip

If i try to call SIP/user at dormain from an adsl connection (with a
modem, without nat) the call is routed succesfuly.

If i try to forward the call from my server i cant route the call...
(i send many INVITE but without any answer)

How can i fix it?

many thanks in advance