lo
—
software loopback network interface
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.
- lo%d: can't handle af%d.
- The interface was handed a message with addresses formatted in an
unsuitable address family; the packet was dropped.
The lo
device appeared in
4.2BSD.
Previous versions of the system enabled the loopback interface automatically,
using a nonstandard Internet address (127.1). Use of that address is now
discouraged; a reserved host address for the local network should be used
instead.