LOOP BACK ADDRESS

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. 127.0.0.1 is also referred to as “localhost”, meaning ‘this computer’.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. Making a connection with a 127.0.0.1 loopback address is the same as making a connection with any remote computer on the network, but avoiding the local network interface hardware. It is widely used by application developers and system administrators with the intention of testing software/applications.

In a word, 127.0.0.0 is the address that refers your system back to its self. 127.0.0.0 checks whether the LAN card is logically connected or not.