TCP and UDP ports

Hi, now we are going to talk about ports in networking,

there are different ports in protocols TCP and UDP.

A port is an application - specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication. The protocols that primarily use the ports are the Transport Layer (layer 4 of OSI model) protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet Protocol Suite.

A port is identified for each address and protocol by a 16-bit number, commonly known as the port number.

The operating system's networking software has the task of transmitting outgoing data from all application ports onto the network, and forwarding arriving network packets to a process by matching the packet's IP address and port number. Only one process may bind to a specific IP address and port combination using the same transport protocol. Common application failures, sometimes called port conflicts, ocurr when multiple programs attempt to bind to the same port numbers on the same IP address using the same protocol.

Applications implementing common services often use specifically reserved, well-known port numbers for receiving service request from client hosts. This process is known as listening and involves the receipt of a request on the well-known ports are defined by convention overseen by the Internet Assigned Numbers Authority (IANA).

Common port numbers

The IANA is responsible for the global coordination of the DNS Root, IP addressing and the other Internet protocol resources. This includes the registration of commonly used port numbers for well-known Internet services.

TCP and UDP ports

An example for the use of ports is the Internet mail system. A server using for sending and receiving email generally needs 2 services. The first service is used to transport email to and from other servers. This is accomplished with a Simple Mail Transfer Protocol (SMPT). The SMTP service application usually listens on TCP port 25 for incoming request. The second service is the Post Office Protocol (POP) wich is used by e-mail client applications on user's personal computers to fetch email messages from the server. The POP server listens on TCP port number 110. Both services mabe running on the same host computer, in which case the port number distinguishes the service that was requested by a remote computer, be it a user's computer or another mail server.

While the listening port number of a server is well defined, the client's port number is often chosen from the dynamic port range. In some applications, the client and the server each use specific port numbers assigned by the IANA. A good example of this is DHCP in wich the client always uses UDP port 68 and the server always uses UDP port 67.

Other example for the use of ports is administrate network equipment, when you need to enter in a equipment to administrate it, you can enter connecting physically or by telnet.

When you use telnet the computer uses port 23 to enter in the network equipment.

You can see more of ports in this webpage: http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers

Thats all!