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

# trunk(4)

link aggregation and link failover interface

## NAME

**trunk** – link aggregation and link failover interface

## SYNOPSIS

**pseudo-device trunk**

## DESCRIPTION

The **trunk** interface allows aggregation of multiple network interfaces as one virtual **trunk** interface.

A **trunk** interface can be created using the **ifconfig** **trunk***N* **create** command.

The driver currently supports the trunk protocols **broadcast**, **failover**, **loadbalance**, **none**, and **roundrobin** (the default). The protocols determine which ports are used for outgoing traffic and whether a specific port accepts incoming traffic. The interface link state is used to validate if the port is active or not.

- **broadcast**

  Sends frames to all ports of the trunk and receives frames on any port of the trunk.

- **failover**

  Sends and receives traffic only through the master port. If the master port becomes unavailable, the next active port is used. The first interface added is the master port; any interfaces added after that are used as failover devices.

- **loadbalance**

  Distributes outgoing traffic through all active ports and accepts incoming traffic from any active port. A hash of the protocol header is used to maintain packet ordering. The hash includes the Ethernet source and destination address and, if available, the VLAN tag, and the IP source and destination address.

- **none**

  This protocol is intended to do nothing: it disables any traffic without disabling the **trunk** interface itself.

- **roundrobin**

  Distributes outgoing traffic through all active ports and accepts incoming traffic from any active port. A round-robin scheduler is used to aggregate the traffic.

The configuration can be done at runtime or by setting up a [hostname.if(5)](/hostname.if/5.md) configuration file for [netstart(8)](/netstart/8.md).

**trunk** does not implement IEEE 802.1AX (formerly 802.3ad) Link Aggregation *(LACP*), which is supported by [aggr(4)](/aggr/4.md).

## EXAMPLES

Create a simple round robin trunk with two [bge(4)](/bge/4.md) Gigabit Ethernet interfaces:

```
# ifconfig bge0 up
# ifconfig bge1 up
# ifconfig trunk0 trunkport bge0 trunkport bge1 \
	192.168.1.1 netmask 255.255.255.0
```

The following example uses an active failover trunk to set up roaming between wired and wireless networks using two network devices. Whenever the wired master interface is unplugged, the wireless failover device will be used:

```
# ifconfig em0 up
# ifconfig ath0 nwid my_net up
# ifconfig trunk0 trunkproto failover trunkport em0 trunkport ath0 \
	192.168.1.1 netmask 255.255.255.0
```

## SEE ALSO

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

## HISTORY

The **trunk** device first appeared in OpenBSD 3.8. Support for 802.3ad Link Aggregation was added in OpenBSD 4.4 and removed in OpenBSD 7.9.

## AUTHORS

The **trunk** driver was written by Reyk Floeter ⟨*reyk@openbsd.org*⟩.

## CAVEATS

The trunk protocols **loadbalance** and **roundrobin** require a switch which supports IEEE 802.3ad static link aggregation; otherwise protocols such as [inet6(4)](/inet6/4.md) duplicate address detection (DAD) cannot properly deal with duplicate packets.

The **trunk** interface takes its MTU from the first **trunkport**. To avoid mismatches, adding a child interface with a different MTU is not permitted.