Essential Concepts - Network Ports

We have seen the various services used for different purposes like IP, HTTP & FTP, SMTP and Telnet & SSH. But we don't know how to use them or how to connect with a specific service for a specific purpose. To know how to use a specific service, we should know how to connect with the server for that specific service; and to request (connect) for a specific service, we should know its address (where it is located). So, in this article we will study where to find a specific service.

Generally ports are used both in hardware and networking. In hardware, we have LAN port, USB ports, HDMI port and so on. While in networking, we have HTTP port, FTP port, SMTP port an so on. In hardware, the ports are visible and we can touch them; while in networking, ports are only logical concepts using which the server's Internet Protocol Suit is designed.

NOTES : 

• HTTP is a protocol providing a specific service while HTTP Port is the location of that Protocol on the server's IP Suit.
• The Internet protocol suite is the conceptual model and set of communications protocols used on the Internet and similar computer networks. It is commonly known as TCP/IP because the original protocols in the suite are the Transmission Control Protocol (TCP) and the Internet Protocol (IP).

Here, we are going to study the Network Ports as hardware ports are no use in hacking (because they require physical access to the computers).

In the internet protocol suite, a port is an endpoint of communication in an operating system. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number. A port number is a 16-bit unsigned integer, so it ranges from 0 to 65535.

A computer may be running several services on it like HTTP (web server), SMTP, FTP and so on. Each of these services are uniquely identified by a number called network port (or simply referred to as port). If a computer wants to avail a specific service from another computer, it has to establish a connection to it on the exact port number where the intended service is running.

For example, if a terminal is to request a web document from a remote server using HTTP, it has to first establish a connection with the remote server on port 80 (HTTP service runs on port 80) before placing the request.

In simple words, port numbers can be compared to door numbers where each door grants access to a specific service on a computer. The following table shows a list of popular services and their default port numbers: 

• 21    :   File Transfer Protocol (FTP)
• 22    :   Secure Shell (SSH)
• 23    :   Telnet remote login service
• 25    :   Simple Mail Transfer Protocol (SMTP)
• 53    :   Domain Name System (DNS) service
• 80    :   Hypertext Transfer Protocol (HTTP) used in the World Wide Web
• 110  :   Post Office Protocol (POP3)
• 143  :   Internet Message Access Protocol (IMAP)
• 443  :   HTTP Secure (HTTPS)

How to use Port Numbers : 

Network Ports are always associated with IP address and Port number. Suppose that you want to connect to a server (with IP address 192.168.43.1) to transfer a web-document or to browser the website. The protocol used for this service is HTTP or HTTPS (for secure service). Here, the request code would me made in the form as :

192.168.43.1:80       OR       192.168.43.1:443

In general, it would be written as :  IP_Address:Port_Number .

Now you would be thinking, Why we always write 192.168.43.1:33455 in the browser when connecting our Laptop with Mobile via Xender.