In the document "UNIX hacking"(found at http://duho.hackaholic.org/pub/hacking_unix/hacking_unix.txt) it says to type this in on a ftp server.

PORT h1,h2,h3,h4,p1,p2

the h* represents the IP address of yourself, and the p* is for the port
address (TCP). When i don't have my local port open i will get an error:

How do you find the port address.