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→Understanding Ports and Services
TCP/IP defines a total 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 which can be provided by an operating system. Such A comprehensive list of such services is provided in the table at the end of this chapter, but such services include HTTP for running a web server, FTP for allowing file transfers, SSH and Telnet for providing remote login access and SMTP for the transport of email messages. Each service is in turn is assigned to a standard TCP/IP port. For example, HTTP is assigned to port 80 while SSH communication take takes place on port 21.
== Securing Ports and Services ==
