Dear friends, I am a network system administrator and I use Kernel 2.6 and iptables as a firewall and NAT. My company decided to install a Windows application called CYF (CALL YOU FREE) in all the desktops of the customer support and sales department. CALL YOU FREE is a communications application to answer incoming webcalls and chat contacts from our company’s website and we are using its freeware version. The issue is that when I tested the application with my computer connected directly to the internet (public IP) it works fine. But when I connected my computer in a private IP behind the NAT I cannot even login to the system. I conclude that there must be a firewall problem, so I opened all ports in the firewall and it works fine. I would like to know how I can find out what port(s) does the application try to access. It seems to be an Asterisk based application using IAX protocol so I tried opening port 4569 but nothing happened. I would appreciate your help because I really don’t know how to find out what port should I open, unless I try one by one, or it may use yet more than one port. Thanks, Ricardo Houssef.