---
name: "lo"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["linux", "freebsd", "openbsd", "macos"]
url: "https://new.carta.tech/lo"
---

# lo(4)

software loopback network interface

## 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)](/hostname.if/5.md) configuration file for [netstart(8)](/netstart/8.md). The **lo0** interface will always exist and cannot be destroyed using [ifconfig(8)](/ifconfig/8.md).

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)](/ioctl/2.md).

## 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)](/inet/4.md), [inet6(4)](/inet6/4.md), [netintro(4)](/netintro/4.md), [hostname.if(5)](/hostname.if/5.md), [ifconfig(8)](/ifconfig/8.md), [netstart(8)](/netstart/8.md)

## HISTORY

The **lo** device appeared in 4.2BSD.