15.1 Understanding Ports and Services

The predominant network communications protocol in use these days is TCP/IP. It is the protocol used by the internet and as such has swept away most of the formerly popular protocols used for local area networks (LANs).

TCP/IP defines a total of 65,535 ports of which 1023 are considered to be well known ports. It is important to understand that these are not physical ports into which network cables are connected, but rather virtual ports on each network connection which can be used by applications and services to communicate over a TCP/IP network connection. In reality the number of ports that are used by popular network clients and services comprises an even smaller subset of the well known group of ports.

There are a number of different TCP/IP services that can be provided by an operating system. A comprehensive list of such services is provided in the table at the end of this chapter, but such services include HTTPS for running a secure...