The
loop interface is a software loopback mechanism which may be used for performance analysis, software testing, and/or local communication. As with other network interfaces, the loopback interface must have network addresses assigned for each address family with which it is to be used. These addresses may be set or changed with the
SIOCSIFADDR ioctl(2). The loopback interface should be the last interface configured, as protocols may use the order of configuration as an indication of priority. The loopback should
never be configured first unless no hardware interfaces exist.
The loopback interface
lo0 is created at boottime, it always exists and cannot be destroyed with
ifconfig(8). Additional loopback interfaces can be created by using the
ifconfig(8) create command.