TCP and UDP are both transport protocols above the IP layer, which are interfaces between IP and upper-layer processes. TCP and UDP protocol port numbers are designed to distinguish multiple applications running on a single device with one IP address from one another.

Since many network applications may be running on the same machine, computers need something to make sure the correct software application on the destination computer gets the data packets from the source machine, and to make sure replies get routed to the correct application on the source computer. This is accomplished through the use of the TCP or UDP "port numbers". In the TCP and UDP header, there are "Source Port" and "Destination Port" fields which are used to indicate the message sending process and receiving process identities defined. The combination of the IP address and the port number is called "socket".

There three port ranges defined by IETF IANA: The Well Known Ports, the Registered Ports, and the Dynamic and/or Private Ports.

• The Registered Ports are those from 1024 through 49151, which are not controlled by IANA and can commonly be used by ordinary user processes or programs executed by ordinary users.
• The Dynamic and/or Private Ports are those from 49152 through 65535, which are typically used as source port by a TCP or UDP client, to communicate with a remote TCP or UDP server, using a well-known port as destination port.

TCP and UDP Port Numbers

Related Terms: UDP, TCP, IP, Socket, Ports

Reference Links: http://www.iana.org/assignments/port-numbers: TCP and UDP port numbers