127.0.0.1

You might have called your ISP’s tech support and got help over the phone at one time or another. If you have done this a few times, one time or another they would have open a command prompt and type a series of numbers like 127.0.0.1. After which you’ll find a bunch of results, which most likely you wouldn’t have understood then since your mind was on your Internet connection and not on the troubleshooting being done.

We will define what 127.0.0.1 is in the discussion below. We will also go over some computer networking basics so that beginners may understand the uses of this string of numbers. Finally we’ll go over the uses of this series of numbers and how it helps you troubleshoot your network connection.

The Loopback Address 127.0.0.1

127.0.0.1 is otherwise known as the loopback address. This is also an IP address that is designated to a computer on a network. Every computer on a network should have a unique IP address so that it can be identified on the network. As with IP addresses, the loopback address also specifies which computer should receive a requested packet of data.

However, the loopback address is categorized under a special group of IP addresses that will not usually be assigned at random to computers on a network. Defined by RFC 3330 by the Internet Engineering Task Force, this address along with 12 others has been designated for special purposes.

This simply means that no computer on any network can have an IP address of 127.0.0.1. If a router or any other network gateway gets a packet intended for this and other special address, that device is required to drop that packet.

The Purpose of the Loopback Address

The name given to 127.0.0.1 also gives its purpose away. The term ‘loopback’ already hints at the purpose for this address. This IP address refers the very computer sending out the packets. For example, you type the command:
ping 127.0.0.1

Your computer will send out four packets and will receive four packets in return with a 0% loss report. This simply means that your computer sent out four packets of data to itself and received all four packets back, thus the name for this special address.

If you get 0% loss on this ping request then you know that your network interface card is working. You also know that the drivers for that device also work and that your computer’s TCP/IP is functioning as well. As you might have guessed, this special IP address is primarily designated to test your own computer.