What is a localhost

The localhost, also known as the “loopback address”, is used to establish an IP connection or a call to a local computer. The loopback address is typically used in the context of networks and provides a means for a user to check the IP stack. The IP address is used to communicate with another computer over the Internet. Entering the IP address establishes a connection to the local host and the computer communicates with itself. Localhost is the name of the virtual server that runs on your own computer.

The IP address is used to access the localhost via the loopback interface. For example, users can use a browser to access and display locally installed websites or homepage. However, the loopback interface is not supported by all operating systems. The name localhost is usually resolved to the loopback address (IPv4) and the loopback address:: 1 (IPv6).

How does loopback – work?

All participants in a network have their own unique addresses. The data packets can reach their destination in this way using the TCP / IP transmission protocol. TCP / IP is also used outside the Internet in local networks. The Internet protocol is responsible for ensuring that the IP address and the subnet behind it can be reached during a transmission.

The assignment of public IP addresses is regulated by an international organization, the Internet Corporation for Assigned Names and Numbers (ICANN). ICANN is also responsible for the assignment of domain names, the entirety of which is known as the Domain Name System (DNS). However, certain address ranges are reserved for special purposes, for example the range from to Today, however, there is no reliable information about why this area was chosen.

According to ETAIZHOU, IP addresses on the Internet are divided into different classes. Class A starts with (reserved address) and ends with 127 is the last block of the class A network. His important position may have been the reason for his selection.

A local network can be set up within this address range. The special thing about this area is that IP addresses are not clearly assigned in it, as is usually the case. This was also set up by ICANN.

If a browser is to access an IP address or a corresponding domain name, the router forwards the request to the Internet, where the request is processed by a server. If you enter the IP address in the address line of your browser, the link will take you to the Google.de homepage.

However, the situation is different for The inquiries to this address will not be forwarded to the Internet. TCP / IP recognizes from the first block (127) that the user does not want to access the Internet, but wants to call himself. This then triggers the loopback.

This is because the loopback device is set to function as a back link to your computer. A virtual interface is created via the operating system. The interface is called lo or lo0 and can also be viewed using the ifconfig command in Unix and Windows systems.

What is localhost used for?

Developers use localhost to test web applications and programs. Network administrators use loopback to check network connections. Another use for the localhost is in the hosts file, which users can use to block malicious websites.

Use for testing purposes

Web servers mainly use the local host for the programs that need to communicate over the Internet. During development, it is important to find out whether the application actually works as designed once it has internet access.

The other functions of localhost are only possible if the necessary files can be found on the internet. For example, there is a difference between opening an HTML document on a local PC or loading it onto a server and accessing it. It makes little sense to release a software product without a test. Hence, loopback is used by developers to test new apps. This way you can establish a network connection while avoiding network errors. The connection just stays entirely in its own system.

When combined with other software, users can even use loopback to allow mobile apps to access desktop server components or to make requests to a specific API.

Block individual websites

Localhost can also be used to block the host files. This file is a predecessor of the Domain Name System (DNS). In the file, IP addresses can be assigned to the corresponding domains. The domain name is translated into an IP address when a website address is entered in the browser. It used to be the hosts file, now global DNS is typically used, but the hosts file is still present in most operating systems. On Windows, the file is located under \ system32 \ drivers \ etc \ hosts, while like on macOS and other Unix systems, it can be found under / etc / hosts.

There are probably only two entries in the hosts file: localhost
:: 1 localhost

To block a website with localhost, it must be entered in the list and assigned to the domain with the IP address When someone or a malicious script tries to access the blocked domain, the browser first checks the hosts file and finds the entry there. The domain name can also be used.

The browser then tries to access the corresponding website on the server with However, it is unlikely that the browser can find the page because the requested file does not exist. An error message is displayed instead of the website. However, if users set up their own test server, the browser might find home.html, which is just its own file.

Conversely, the TCP / IP protocol does not accept any external requests to, as this would mean that attackers could try to sneak into a system. Packets reportedly appearing on the Internet from reserved IP addresses such as are known as Mars packets.

While this technique works, using localhost as a method to prevent access to unwanted websites is not the best solution. The main reason for this is that the administrator has to manually remove the entry when access to these websites is needed again. This can only be done by the administrator who created the first entry. However, he can also block other people who for whatever reason need to reach the particular site.

The hosts file can have a significant impact on Internet browsing security. Although the file is useful for blocking malicious websites, criminals can also tamper with it. Users should therefore ensure that they are not copying entries from other websites without first checking them. This is the only way to prevent malware from attempting to make entries without users noticing.

Run a speed test through the localhost

Sending a ping request is the most common use for the loopback address. Using the Windows Command Prompt, users can test their connection and identify performance problems that the computer may be currently facing.

This is how a ping request is made to localhost

The following commands apply to Windows, macOS, and Linux. Under Windows they are entered in the “Command Prompt” window, under macOS and Linux in a “Terminal window”. It is recommended to be logged in as an administrator.

  • Open the run function (Windows task + R)
  • Enter from “cmd” + Enter
  • Input: ping or ping localhost

The results are displayed on the screen. The data shown include the number of sent, received and lost data packets and the approximate cycle time of the data transmission.

What is the difference between and localhost? is the most commonly used loopback address. This means that over 16 million IP addresses can be used explicitly for the loopback functionality. A loopback address enables the computer to exchange information with itself using network connection protocols.

In this sense, a loopback address represents a virtual network device that establishes a network connection with only one endpoint. This means that the network begins and ends on the same device, that is, on the local computer.

Localhost describes the communication port that connects to the source server. This means that the port can also be used to emulate a network, even if such a network does not exist or is inaccessible.

On most computers, localhost and are functionally identical. However, the word localhost is a designation for the IP address, not the address itself. It can be forwarded to any IP address, including one outside the reserved address block.
When switching from Windows to a Unix / Linux system, users are likely to find that loopback is almost synonymous with localhost. Therefore administrators can use the hosts file to redirect the loopback to

In summary, using localhost is just an alternative way to access We can say that the two terms are synonyms. There are also a number of IP addresses designed for creating local networks: –

What is a localhost