---
name: "if_epair"
section: "4freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/epair/4freebsd"
---

# if\_epair(4freebsd)

A pair of virtual back-to-back connected Ethernet interfaces

Part of [epair(4freebsd)](/epair/4freebsd.md).

## NAME

**epair** – A pair of virtual back-to-back connected Ethernet interfaces

## SYNOPSIS

To compile this driver into the kernel, place the following line in your kernel configuration file:

**device epair**

Alternatively, to load the driver as a module at boot time, place the following line in [loader.conf(5)](/loader.conf/5.md):

```
if_epair_load="YES"
```

## DESCRIPTION

The **epair** is a pair of Ethernet-like software interfaces, which are connected back-to-back with a virtual cross-over cable.

Each **epair** interface pair is created at runtime using interface cloning. This is most easily done with the [ifconfig(8)](/ifconfig/8.md) **create** command or using the *cloned\_interfaces* variable in [rc.conf(5)](/rc.conf/5.md). While for cloning you only give either *epair* or *epair\<n\>* the **epair** pair will be named like *epair\<n\>\[ab\]*. This means the names of the first **epair** interfaces will be *epair0a* and *epair0b*.

Like any other Ethernet interface, an **epair** needs to have a network address. Each **epair** will be assigned a locally administered address by default, that is only guaranteed to be unique within one network stack. To change the default addresses one may use the SIOCSIFADDR [ioctl(2)](/ioctl/2.md) or [ifconfig(8)](/ifconfig/8.md) utility.

The basic intent is to provide connectivity between two virtual network stack instances. When connected to an [if\_bridge(4)](/if_bridge/4.md), one end of the interface pair can also be part of another (virtual) LAN. As with any other Ethernet interface, **epair** can have a [vlan(4)](/vlan/4.md) configured on top of it.

## SEE ALSO

[ioctl(2)](/ioctl/2.md), [altq(4)](/altq/4.md), [bpf(4)](/bpf/4.md), [if\_bridge(4)](/if_bridge/4.md), [vlan(4)](/vlan/4.md), [loader.conf(5)](/loader.conf/5.md), [rc.conf(5)](/rc.conf/5.md), [ifconfig(8)](/ifconfig/8.md)

## HISTORY

The **epair** interface first appeared in FreeBSD 8.0.

## AUTHORS

The **epair** interface was written by Bjoern A. Zeeb, CK Software GmbH, under sponsorship from the FreeBSD Foundation.