127.0.0.1 – Localhost (Loopback) Address

127.0.0.1 is a special purpose IPV4 addresses. It’s often called a localhost address or a loopback address and it’s an address that specifies the local computer (the computer you are currently working on). So, 127.0.0.1 is your computer from your computer’s point of view. Also, any 127.x.x.x address has the same purpose and can be used instead of 127.0.0.1. The whole range of addresses starting from 127.0.0.1 to 127.255.255.255 is reserved in IPV4. There’s also an IPV6 version of this address and it looks like this  ::1.In IPV4, you have the whole range of reserved addresses but in IPV6, there is only one.

The localhost address relates directly to localhost hostname (the computer you are currently working on or THIS computer). It cannot be used for communicating with other devices on the network (like any private IP address). For that, you have the IP address assigned to your device by your router. 127.0.0.1 is used only by your local machine and only for some special purposes like testing purposes, network administration and maintenance (we are going to talk about this later).

Why this exact address and not some other?

IETF (Internet Engineering Task Force) and IANA (Internet Assigned Numbers Authority) are the organizations in charge of IPV4 standards and they reserved the whole 127.0.0.0/8 block of IP addresses for loopback purposes. The Class A ends with 127.0.0.0, and the first address that can be assigned is 127.0.0.1. There’s no some deeper meaning behind the decision to reserve this exact block, it was an unused block of addresses.

How it works and how to use it?

127.0.0.1 is recognized by the TCP/IP protocol as a special purpose address. TCP/IP checks the data packages before sending them to the network and if the destination address is 127.0.0.1, the TCP/IP will re-route that data to your local machine. Any data sent to the loopback address will never reach outside the network.

There are several reasons to use 127.0.0.1 IP address. It’s often used for testing purposes. When you ping 127.0.0.1 from your computer you can determine whether the TCP/IP protocol is working correctly without connecting to the network (or to some other computer on that network). You can also use it to check your network card. When you are pinging this address, you won’t actually generate any traffic. So, let’s see how to test these things and how to ping 127.0.0.1 on Windows PC.

You just have to open Command Prompt, type in ping 127.0.0.1, and press ENTER. You will get something like this

You should get 4 replies from this address (from your computer communicating with itself) and a simple ping statistic with a number of data packets sent and received, loss percentage, and an approximate round-trip time.

Since all the addresses from the 127.x.x.x block of addresses are the same and they are all reserved for special purposes, you can ping any address starting from 127.0.0.1 to 127.255.255.255 and you should get the same results if everything is in order (see the example below).

So, we’ve got the same results with the address from the example (127.230.87.25). You can use any 127.x.x.x address for testing. 127.0.0.1 is simply more popular than any other.

You can also use that IPV6 version of 127.0.0.1 (::1) for testing purposes and the results will be similar.

None of these addresses will generate any traffic.

You can also use ping localhost command instead of the numbers and you will get the same results.

Localhost is Microsoft’s name for 127.0.0.1 but it’s basically the same thing. Unlike pinging the address (IPV4 or IPV6 version of the address), pinging the localhost will create some traffic because it includes the name of the computer (in this case Boba-PC). If you don’t want to create any traffic, you should use the address. Instead of pinging the localhost you can ping the loopback and get the same results.

If you get the results similar to those in the pictures, you can be assured that there is nothing wrong with your network adapter and TCP/IP.

127.0.0.1 is also used by network administrators (for maintenance and administrative purposes) and by developers (testing purposes).

Let’s say you are an administrator hosting information via HTTP on your local computer for a certain number of users. Those users connect to the server in a usual way (through a browser or some app) but you can use this localhost address (127.0.0.1) to connect to the server and lessen the network load. Since it’s a local address, any request made by the local machine is considered local and it doesn’t have to travel on to the network. That way, you won’t create any traffic while moving data and maintaining the network (you can do all the administrative and maintaining job locally).

The loopback is also used by software developers for testing purposes. That way, they can test their apps and programs autonomously without using network interface hardware (by using 127.0.0.1 they simulate the network interface without actually accessing the network).

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