There are a number of different TCP/IP services that can be provided by an operating system. 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. 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. TCP/IP defines a total of 65,535 ports of which 1023 are considered to be well known ports.

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). The predominant network communications protocol in use these days is TCP/IP. For more complex firewall requirements, a detailed overview of the firewalld firewall will be covered in the chapter entitled РІР‚СљBasic Ubuntu Firewall Configuration with firewalldРІР‚Сњ. The configuration of a firewall on an Ubuntu system will be covered in РІР‚СљUsing gufw and ufw to Configure an Ubuntu FirewallРІР‚Сњ. The goal of this chapter is to cover some of the basic concepts of firewalls, TCP/IP ports and services.

If you would like to learn about iptables we recommend: Entire books can, and indeed have, been written about configuring iptables. Ubuntu is supplied with powerful firewall technology known as iptables built-in. Similarly, any internal network must have some form of firewall between it and an external internet connection. Any computer connected directly to an internet connection should ideally run a firewall to protect against malicious activity. A firewall is a vital component in protecting an individual computer system or network of computers from external attack (typically from an internet connection).

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