What is Port Number or Define a Port Number

Some protocol suites are used to communicate with computers to computers or other devices. Such as TCP/IP, IPX, AppleTalk, etc. Each protocol contains a thing called a port number.

In this tutorial, we are going to talk about what is the port number and why it is being used.

Each protocol contains a lot of port numbers. A server is going to the listening mode using these port numbers. With this port number, the server keeps hearing whether any request is coming. A server uses different port numbers for all the services it provides. Such as port number 80 is used to provide web service, port number 1433 is used to provide database service, port number 21 is used to provide file transfer service or download service.

Now if any server wants to provide web service then that server will go to port number 80 and will be in listening mode. The server will be ready to receive any request that is coming through port number 80. If a client brings a request to reach a web page, then that client has to come with the required port number 80. It is predefined. When a request reaches the server through port 80, then the server realizes that it is bringing the request of the web page. The server then provides the data of the web page to the client.

The way a web service's port number is predefined in the same way, a dedicated port number is predefined for each service.

So this is called the port number. Protocols allow devices to communicate with each other and the port is used to identify which service the client is requesting. Using the port number, it will identify whether it came with a database request or a file download request.

Some well-known protocols such as the HTTP protocol uses port 80, FTP protocol uses port 20 and 21, HTTPS protocol uses port number 443, SMTP protocol uses port number 25, DNS uses port number 53, etc.