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. 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.

# 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), ifconfig(8)

# HISTORY

The `lo` device appeared in 4.2BSD.

# BUGS

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.

September 3, 2006 | NetBSD 9.5