127.0.0.1 is a special Internet Protocol (IP) address that points to your own computer. It is also referred to as the local host or loopback address. Local host is sometimes commonly referred to as My computer. TechGeek has even created a t-shirt that reads “there’s no place like 127.0.0.1” which translates to “there’s no place like home.” This special top level domain loopback address is a communications protocol with only one end point. It allows you to access a shared, world-wide file system through your web browser. Its intended purpose is to identify the current local computer reserved at the top level of the DNS to prevent conflict with remote addresses.

Every computer connected to the Internet has a unique IP address, but 127.0.0.1 is reserved for each machine so as to be used whenever one needs to communicate with a network service running on the same machine.

When you type a URL for a certain site, your browser first tries to locate the site on your computer using a local IP file know as Host file. If the IP address is not detected on your computer then the browser will now redirect to a proxy server or some other remote host to look for the IP of the website that you want.

Network software and utilities can use 127.0.0.1 to access a local computer’s TCP/IP network resources. Messages sent to this loopback IP address are automatically re-routed back to the receiving end of the TCP/IP stack.

Typically all IP addresses in the range 127.0.0.1 – 127.0.0.8 are reserved as the Internet loopback address. The Internet Society states that “A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host. This is ordinarily implemented using only 127.0.0.1/32 for loopback, but no addresses within this block should ever appear on any network anywhere.”

Thus, no computer connected to the Internet, or any other TCP/IP compliant network, can identify itself as 127.0.0.1. RFC 3513 as the specification says: “The loopback address must not be used as the source address in IPv6 packets that are sent outside of a single node. An IPv6 packet with a destination address of loopback must never be sent outside of a single node and must never be forwarded by an IPv6 router. A packet received on an interface with destination address of loopback must be dropped.”

Local host is mainly useful for testing purposes. For instance if one is developing a site then they can test it on http://localhost without having to connect and upload to a server. It can also be used to test if a machine’s network interface card and TCP/IP implementation are all functioning correctly by sending a ping request to 127.0.0.1. Convincing inexperienced users to connect or hack into 127.0.0.1 is a frequent joke on the Internet. Of course the address is defined to route back to the host machine and therefore someone without this knowledge will think they are accessing a remote computer when in reality all they are doing is looping back to their own machine.

For more information on 127.0.0.1 read What is 127.0.0.1?

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