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TRUNK(4) Device Drivers Manual TRUNK(4)

trunklink aggregation and link failover interface

pseudo-device trunk

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

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

The driver currently supports the trunk protocols broadcast, failover, lacp, 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.

Sends frames to all ports of the trunk and receives frames on any port of the trunk.
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.
Uses the IEEE 802.3ad (renamed to 802.1AX in 2014) Link Aggregation Control Protocol (LACP) and the Marker Protocol to increase link speed and provide redundancy. LACP trunk groups are composed of ports of the same speed, set to full-duplex operation. This protocol requires a switch which supports LACP. By default, the LACP implementation uses active-mode LACP, slow timeout, and 0x8000 (medium) priority as system and port priorities.
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.
This protocol is intended to do nothing: it disables any traffic without disabling the trunk interface itself.
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) configuration file for netstart(8).

Create a simple round robin trunk with two bge(4) Gigabit Ethernet interfaces:

# ifconfig bge0 up
# ifconfig bge1 up
# ifconfig trunk0 trunkport bge0 trunkport bge1 \ netmask

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 \ netmask

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

The trunk device first appeared in OpenBSD 3.8.

The trunk driver was written by Reyk Floeter <>.

The trunk protocols loadbalance and roundrobin require a switch which supports IEEE 802.3ad static link aggregation; otherwise protocols such as inet6(4) 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.

August 24, 2020 OpenBSD-7.2