Why use port number after URL?

Port Number:
In computer networking, port numbers are part of the addressing information used to identify the senders and receivers of messages. 

Port numbers are associated with TCP/IP network connections. They allow different applications on the same computer to share network resources simultaneously.

As computers and internet became popular and offered many services, it became necessary to identify each service uniquely, and hence in computer networks the term port was introduced.

The port number is a 16 bit binary number in the TCP. Therefore the port number is in the range of 0-65535.The port numbers are divided into three ranges.

• Well Known ports.
• Registered Ports.
• Dynamic Ports/Ephemeral ports

Well known Ports

The port numbers ranging from 0-1023.They are assigned to standard server processes such as FTP, Telnet. most of the popular services are under these range only such as 21 for FTP,80 for HTTP,443 for HTTPS, 23 for TELNET and 22 for SSH.

Registered Ports:

The ports ranging from 1024 - 49151 are to be registered with IANA to prevent duplicating. They can be used for proprietary server processors or nay client process. Registered ports; meaning they can be registered to specific protocols by software corporations.

Dynamic Ports:

49152 to 65536 - Dynamic or private ports; meaning that they can be used by just about anybody.

How to Find an IP Address and Port Number

• Type “ipconfig” and press “Enter.” Your IP address should be listed
• Type “netstat -a” and press “Enter.” A list of all your active TCP/IP connections will populate. The port numbers appear after the IP address with a colon separating the two. For example, if your IP address is 192.168.1.1 and you see an entry for 192.168.1.1:2869, it means port 2869 is open. If you see port numbers listed after “0.0.0.0,” it means that all network adapters on your computer have the listed ports open and in the state indicated in the “State” column on the right. Port numbers listed after “127.0.0.1” are open on your computer’s loopback address only. The loopback address is a virtual network interface mainly used for connectivity testing purposes. 
  
  
  
  
  
  
  
  

  References:

  
  

  1. https://www.quora.com/What-is-port-number-and-port-address
  2. https://www.lifewire.com/port-numbers-on-computer-networks-817939
  3. http://www.ipaddressfinder.info/whatisportnumber.html
  4. http://smallbusiness.chron.com/ip-address-port-number-55788.html
  5. http://www.webopedia.com/quick_ref/portnumbers.asp
  6. https://www.techopedia.com/definition/15702/port-number