Firewall for VoIP box

[Dmitry Mishchenko]

Hello,

We have the following configuration: FreeBSD router with 2 network cards.
- first card has a real IP and connected to internet (lets say 
65.1.1.1). There is a  ipfw firewall which control traffic to this card.
- second card has another real IP (lets say 65.1.1.2) and connected to 
Quintum VoIP box.

VoIP box has also its own real IP (lets say 65.1.1.3).

How should firewall be configured for card #2 for allowing VoIP traffic?
What ports should be open for normal VoIP work?


Thanks,
Dmitry