15.4 Well Known Ports and Services

Before moving on to cover more complex firewall rules, it is first worth taking time to outline some of the key services that can be provided by an Ubuntu system, together with the corresponding port numbers:

Port	Assignment	Description
20	FTP	File Transfer Protocol (Data) - The File Transfer protocol provides a mechanism for transferring specific files between network connected computer systems. Transfer is typically performed using the ftp client. Most modern web browsers also have the ability to browse and download files located on a remote FTP server. FTP uses TCP (rather than UDP) to transfer files so is considered to be a highly reliable transport mechanism. FTP does not encrypt data and is not considered to be a secure file transfer protocol. The use of Secure Copy Protocol...