System Administration Guide: IP Services

Loopback Address

In Example 5–1, the IPv4 address is the loopback address. The loopback address is the reserved network interface that is used by the local machine to allow interprocess communication. This enables the host to send packets to itself. The ifconfig command uses the loopback address for configuration and testing, as explained in ifconfig Command. Every machine on a TCP/IP network must use the IP address for the local host.