Network Port

What is a Network Port ?

Port is an application-specific or process-specific software construct serving as a communications endpoint used by Transport Layer protocols of the Internet Protocol Suite such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). A specific port is identified by its number commonly known as the port number.

Transport Layer protocol, such as TCP, UDP, SCTP, and DCCP specify a source and destination port in their packet headers. A port number is a 16-bit unsigned integer, ranging from 0 to 65535. A process "binds" to a particular port to send and receive data, meaning that it will listen for incoming packets whose destination port matches that port number, and/or send outgoing packets whose source port is set to that port number. Processes may bind to multiple ports.

Applications implementing common services will normally listen on specific port numbers which have been defined by convention for use with the given protocol — see list of TCP and UDP port numbers. Typically, these will be low port numbers, and in UNIX only processes owned by the super user can create ports with numbers from 0 to 1023. This is for security to prevent un trusted processes from acting as system services. Conversely, the client end of the connection will typically use a varying, high port number (ephemeral port).

Because the port number is a part of the packet header, it is readily interpreted not only by the sending and receiving computers, but also by other components of the networking infrastructure. In particular, firewalls are commonly configured to respond differently to packets depending on their source and/or destination port numbers. Port forwarding is an example application of this.

Processes implement connections to transport protocol ports by means of sockets. A socket is the software structure used as the transport end-point. It is created by the process and bound to a socket address which consists of a combination of a port and an IP address. Sockets may be set to send/receive data in one direction at a time, called half duplex, or simultaneously in both directions, called full duplex. In addition to the transport protocols, sockets are also used by interprocess communications protocols within a single host.

Because different services commonly listen on different port numbers, the practice of attempting to connect in sequence to a wide range of services on a single computer is commonly known as port scanning. This is usually associated either with malicious cracking attempts or with a search for possible vulnerabilities to help prevent such attacks.

Port connection attempts are frequently monitored and logged by computers connected to networks. The technique of port knocking uses a series of port connections or "knocks" from a client computer to enable a server connection.

IANA

The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of the DNS Root, IP addressing, and other Internet protocol resources.

A list of registered ports can be found on the IANA Website - http://www.iana.org/assignments/port-numbers

PORT NUMBERS

The port numbers are divided into three ranges: the Well Known Ports,the Registered Ports, and the Dynamic and/or Private Ports.

The Well Known Ports are those from 0 through 1023.

DCCP Well Known ports SHOULD NOT be used without IANA registration.

The registration procedure is defined in [RFC4340], Section 19.9.

The Registered Ports are those from 1024 through 49151.

Some Of the commonly used Ports are mentioned below.

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