A brief tutorial on TCP ports 20/21, 23, 25, 80/8080 and 110 as well as a definition of the reserved port range 0-1024... Probably useful for newcomers to networking, and those who wish to set up a firewall.

Note that ifn you are protecting against access to those ports on your machine, they are local ports, and if you are restricting access to those services on other machines, from the machine you're configuring, the ports number is a remote port number.