TCP/IP Ports


TCP uses the notion of port numbers to identify sending and receiving application end-points on a host, or Internet sockets. Each side of a TCP connection has an associated 16-bit unsigned port number (1-65535) reserved by the sending or receiving application. Arriving TCP data packets are identified as belonging to a specific TCP connection by its sockets, that is, the combination of source host address, source port, destination host address, and destination port. This means that a server computer can serve simultaneously several services and to several clients, as long as a client doesn't use same source port to connect multiple times to one destination port.

Port numbers are categorized into three basic categories: well-known, registered and dynamic/private. The well-known ports are assigned by the Internet Assigned Numbers Authority (IANA) and are typically used by system-level or root processes. Well-known applications running as servers and passively listening for connections typically use these ports. Some examples include: FTP (21), TELNET (23), SMTP (25) and HTTP (80). Registered ports are typically used by end user applications as ephemeral source ports when contacting servers, but they can also identify named services that have been registered by a third party. Dynamic/private ports can also be used by end user applications, but are less commonly so. Dynamic/private ports do not contain any meaning outside of any particular TCP connection.


source - Transmission Control Protocol. (2006, August 29). In Wikipedia, The Free Encyclopedia. Retrieved September 2, 2006, from

Through the use of port filtering and redirection, not only does Hautspot's captive portal technology interact with the end user, but Hautspot is also able to direct certain traffic to specific internal hosts utilizing the firewall built into the Sputnik-powered access point or gateway device.