What is 127.0.0.1?
127.0.0.1 is the standard IP address used for a loopback network connection.
This means that if you try to connect to 127.0.0.1, you are immediately looped back to your own machine.
If you telnet, ftp, etc... to 127.0.0.1, you are connected to your own machine.
In other words, 127.0.0.1 is you.
For example, if your system was named "joker", and you attempted to telnet to 127.0.0.1, you would see:
# telnet 127.0.0.1 Trying 127.0.0.1... Connected to joker Escape character is '^]'.
Convincing newbie's to connect to 127.0.0.1 is a frequent joke on the Internet.
Another name for 127.0.0.1 is localhost.
Although 127.0.0.1 is the most commonly utilized address for localhost, any IP address in the 127.*.*.* range should also function in the same manner.
127.0.0.1 Defined in the Internet RFC's
The proper use of 127.0.0.1 is defined in RFC 3330: Special-Use IPv4 Addresses:
127.0.0.0/8 - This block is assigned for use as the Internet host loopback address. 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.
The IPv6 version of localhost is defined in RFC 3513: Internet Protocol Version 6 (IPv6) Addressing Architecture as ::1/128.
