In TCP/IP, a port is the mechanism that allows a computer to simultaneously support multiple communication sessions with computers and programs on the network. A port is basically a refinement of an IP address; a computer that receives a packet from the network can further refine the destination of the packet by using a unique port number that is determined when the connection is established. A number of "well known" ports have reserved numbers that correspond to predetermined functions.
This appendix describes the Windows NT Server and Windows NT Workstation default port assignments for TCP/IP and User Datagram Protocol (UDP). The Services file controls port assignments used by Windows NT Server and Windows NT Workstation. The Services file is located in the \systemroot\Winnt\System32\Drivers\Etc\Services directory.