LO(4) | Device Drivers Manual | LO(4)

# NAME

`lo` — software loopback network interface

# SYNOPSIS

`pseudo-device loop`

# DESCRIPTION

The `loop` interface is a software loopback mechanism which may be used for performance analysis, software testing, and/or local communication.

A `loop` interface can be created at runtime using the `ifconfig lo` N `create` command or by setting up a hostname.if(5) configuration file for netstart(8). The `lo0` interface will always exist and cannot be destroyed using ifconfig(8).

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).

# DIAGNOSTICS

lo0: can't handle afX.
  The interface was handed a message with addresses formatted in an unsuitable address family; the packet was dropped.

# SEE ALSO

inet(4), inet6(4), netintro(4), hostname.if(5), ifconfig(8), netstart(8)

# HISTORY

The `lo` device appeared in 4.2BSD.

April 29, 2018 | Debian