How to find port number

In our previous post on How to test if a port is open on a server or PC, we have indicated that in TCP/IP networking,  port 25 is used in SMTP (Simple Mail Transfer Protocol), port 110 is for POP3 (Post Office Protocol) and so on. Anyway, where can a user find the port number information?


Of course, the easiest way is to get this information by using search engine like Google, Yahoo or MSN. However, this information is also available in your computer too. The list of port number information can be found in a services file available in Windows and Unix systems.

In Windows, the services information file is available at the following location in your computer hard disk:

C:\Windows\System32\drivers\etc\services

There are other important files located here too, however, we will go through it in our future posts.



In Unix systems, you may find the list in the /etc/services file.

Following is something you may find in this file:



So, by referring to this file, you know that ftp is using port 21 of tcp protocol and so on.

The other way, which is highly recommended is to refer to port number file from IANA.