One port is an internal address (interface is) that is predominantly in the network protocols, TCP (Transmission Control Protocol) and UDP (user datagram protocol) is used for data packets, the right services to the application layer (TCP / IP model) assigned. These data packets are forwarded to the appropriate addresses (ports) through in them and the respective protocols and the information contained therein by each service or protocol processing. An example: data packets that include the TCP port 80 will be addressed by the HTTP protocol of a web server (eg Apache accepted) and processed. A request from this port through a Web browser may have the effect that the web server then a website has. This website may in turn be displayed using a web browser. In general, programs use ports to each other, to communicate through data transmission over a given address (port number), in a network.
In most networks, but listening to the so-called Internet Super Server inetd or its improved version known to him at the port. Only when data arrives on a particular port, the actual network services (daemons) starts. In the above example was taken from me that the Apache Web server listens on TCP port independently with the number 80th Ports can be categorized. So-called Well Known Ports (1-1024) are assigned by the IANA (Internet Assigned Numbers Authority) special protocols ports. Ports with port numbers greater than 1024 are known as Registered Ports, and Dynamic and / or Private Ports. Registered ports can of application vendors as needed for your own – sometimes even proprietary protocols – are registered. Private ports can be used variable, as they are not registered for a specific application or its Protocol. The assignment of the Protocols to the port numbers on most Unix-like operating systems and Unix derivatives – like in the case of Linux – in the file / etc / services.