A Port Number is a 16 bit binary number in the Transmission Control Protocol or TCP in the field of computer networking used to identify a specific port. With a port number, one may identify the information of the sender and receiver of messages in the network when it arrives at a server.

Port Numbers range from 0 to 65535. Registered Ports are those ranging from 1024 – 49151. These ports are registered by the Internet Assigned Numbers Authority so as to avoid duplication of port numbers. Well-known port numbers registered by the IANA with their protocols are as follows:

7 for Echo which literally echoes a received datagram to the sender

11 for Users

19 for Chargen which returns a string of characters

20 for FTP, Data or File Transfer Protocol for Data Connection

21 for FTP, Control or File Transfer Protocol for Control Connection

The Dynamic Ports are port numbers ranging from 49152 – 65535. This range of numbers is constantly used since the uses for these numbers are temporary.

The lower port numbers are basically for internet protocols. The default Hypertext Transfer Protocol or HTTP port number is 80. On the other hand, the default Hypertext Transfer Protocol Secure or HTTPS port number is 443. The Hypertext Transfer Protocol is a combination of HTP and SSL/TLS protocol enabling a secure identification of a web server. HTTPS are more often used for online payment transactions.

Though 80 and 443 are already the default port numbers for http and https respectively, there is a possibility to change this by a certain command. However, you should use another port if you want to configure the http and https servers. The command for changing the https port number is as follows:

Router(config)#ip http secure-port port_number

Once the https port number has been changed, you must immediately inform other people of the change with the instructions of specifying the port number assigned in the URL. They can do this in this format:

https://device: port#

Here is an example of changing the https port number:

From the default HTTPS port number, 80, we change the port number to 900. The command should look like this:

Ip http secure-port 900