What is a Network Port ?

Saturday, September 19, 2009

In order to connect the computers the each computer was given an I.P. (Internet Protocol) Address which a unique number given to a computer on the internet. But to connect one or more application(s) of one computer to one or more application(s) of another computer we use the combination of Internet Protocol address as well as ports.
There are 65,536 ports.whenever you send or receive any data from your PC your data is sent thorugh the ports.

Port numbers can be any number from 0 to 65535. This range is split into three main categories:

* 0 to 1023 are "well known ports", meaning they are reserved for special services like FTP(21), SMTP (25), HTTP (80), POP3 (110), etc.

* 1024 to 49151 are "registered ports", meaning they are registered for services.

* 49152 to 65536 are "dynamic and/or private ports", meaning that everyone can use these as required.

Assume That you are chatting with your friend, you and your friend have both yahoo messenger as well as Gtalk . Now you and your friend are logged in to yahoo messenger as well as gtalk.

When you send a message from your yahoo messenger to your friend he receives message on yahoo messenger and when you send a message from gtalk your friend of course receives message on Gtalk and not on yahoo messenger.

So how come it possible that when you send a message from yahoo messenger to your friend he receives messages on yahoo messenger itself and not on the Gtalk ?
Here the concept of ports comes into picture.

yahoo messenger uses port number 5101 and when you send message to your friend his yahoo messenger receives message on port number 5101 and not on the port which Gtalk uses that is port number 5222.

So in This way different application on your computer uses different ports for example your counter strike server may user port number 27015 by default or your web browser uses port 80 by default.

Port numbers are managed by the IANA (Internet Assigned Numbers Authority).
Click here to view the list of port numbers maintained by IANA.

This way connection between the application takes place and hope you understood what are ports this tutorial is necessary to understand our next upcoming post that is on port scanning.