What Is Localhost?

A good way to think of localhost, in computer networking, is to look at it as “this computer”. It is the default name used to establish a connection with your computer using the loopback address network.

The loopback address has a default IP (127.0.0.1) useful to test programs on your computer, without sending information over the internet. This helps when you are testing applications that aren’t ready for the world to see.

When you call an IP address from your computer, you usually try to contact a different computer over the internet. However, with the loopback address, you are calling the localhost, aka your computer.

If you want to learn about computer networking, it’s important to understand the language that you’ll run into. No better place to start than learning about localhost.

Download glossary for web beginners

Localhost Explained in a Video Tutorial

Too busy to read? Check out our video tutorial instead.

What is 127.0.0.1 and a Loopback Address?

Like an IP address, when typing google.com in a web browser it directs you to its local hosting website, Google’s main page. So where will localhost take you? It will take you to your computer. This situation is also known as a loopback address.

Like any other domain name, localhost also has an IP (Internet Protocol) address. The addresses range from 127.0.0.0 to 127.255.255.255, but it’s normally 127.0.0.1. Trying to open the address 127.0.0.1 in an IPv4 connection will trigger a loopback, referring you back to your own web server. You can also start a loopback back to your own server with an IPv6 connection by entering :1.

Fun fact: the first section of the address – 127 – is reserved only for loopbacks. For that reason, Transmission Control Protocol and Internet Protocol (TCP/IP) immediately recognize that you want to contact your computer after entering any address that starts with these numbers. That is why no websites can have IP addresses that begin with 127. If initiated, this action will create a loopback device; which is a virtual interface inside your computer’s operating system (OS).

What Is Localhost Used For?

Despite its simple meaning, localhost is useful if you are a developer, network administrator, and for testing. Generally, there are three advantages that loopback offers:

Program or Web Application Test

Using localhost is one of the main uses for developers; especially if they are creating web apps or programs that require an internet connection. During development, tests are run to see if the applications actually work. By using a loopback to test them, developers can create a connection to the localhost, to be tested inside the computer and system they are currently using.

Since your OS becomes a simulated web server once a loopback is triggered. You can load the necessary files of a program into the web servers and check its functionality.

Site Blocking

Another interesting trick is blocking websites that you do not wish to access. Loopback is useful for preventing your browser from entering harmful sites, like ones containing viruses.

Before learning how this works, however, you need to know what “hosts file” is and its role in this context. As you already know, all domains have IP addresses. You can enter a website because the DNS or Domain Name System searches for the appropriate IP address under which the site is registered.

Your computer helps improve this process by storing a hosts file for every site you have visited. This file contains the IP address and the domain names of websites. You can change the IP address into 127.0.0.1 and the site which hosts file you modified redirects you to the localhost instead.

An example could be a company’s computer admin blocking access to a website.

Speed Test

As a network administrator, you will want to make sure that all equipment and the TCP/IP are in top condition. You can do this with a connection test and by sending a ping request to the localhost.

For example, you can easily open the command prompt or the terminal and enter “ping localhost” or “ping 127.0.0.1”. The localhost test will show how well everything performs, from the number of data packets received, sent, or lost, to how long the data transmission takes. If there are any problems, you can immediately fix any that occur.

For more detailed testing and comprehensive insights, modify the packets sent to the localhost. Check out our Linux ping command tutorial to learn how to do so.

Conclusion

Now you understand that localhost is not merely a technical term for your computer. It is a default name that enables you to test programs and even close access to websites. If you aspire to be an IT technician, it is essential to know what is localhost and how to use a loopback according to your needs.