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14 Identify commonly used TCP and UDP default ports

Multiple applications and services are offered by the TCP/IP protocol. A mechanism is required to identify the protocol for which the communication coming in is meant for. The mechanism that does the necessary to achieve this for the suite is the port.

With every individual TCP/IP protocol that is a part of the suite is an associated port. On receipt of communication the target port number is checked for the destination. After the destination is ascertained, the request is then forwarded to that particular protocol. There are 65,535 ports available in total. This number can be broke down into three categories:

- Well Known Ports: The numbers of these ports ranges from 0 to 1023.

- Registered Ports: The port numbers of this category range from 1024 to 49151. There are applications or services that require consistent port assignments. Registered ports are used by these applications.

- Dynamic or Private Ports: The port numbers of this category ranges from 49152 to 65535. These are not specifically designated to any protocol or service and can be used by any application.

Communication is established on a well known port by the protocol and then it moves to a port in the dynamic range. In this range it continues with the rest of the communication. Understanding port assignments acquires importance for the reason that Administrators are often required to specify port assignments. They are required to do this while working and configuring a network for security. The table given below illustrates the port assignments which are well known.

Table 4: Common TCP/IP Suite Protocols and their Assignments

The above mentioned are the standard ports assigned to each of the protocols. Assigning other protocols is also possible.