SIP and NAT do not work nicely together. While using an external user to our Asterisk box there maybe up to 6 sessions at one time for just a single call. We need to get some IAX trunks happening.
Oh and for future reference the netscreen needs a "special" command set before it will forward a range of ports through a VIP.
marian-> set vip m ?
multi-port enable multiple virtual port creation
marian-> set vip multi-port