lo(4)

NAME

lo - software loopback network interface

SYNOPSIS

device loop

DESCRIPTION

The loop interface is a software loopback mechanism which

may be used for
performance analysis, software testing, and/or local commu

nication. 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 pri

ority. The
loopback should never be configured first unless no hardware

interfaces
exist.

DIAGNOSTICS

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.

SEE ALSO

inet(4), intro(4)

HISTORY

The lo device appeared in 4.2BSD.

BUGS

Previous versions of the system enabled the loopback inter

face 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.

BSD June 5, 1993

BSD