TRUNK(4)

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 trunkN create command. It can use different link aggregation protocols specified using the trunkproto proto option. Child interfaces can be added using the trunkport child-iface option and removed using the -trunkport child-iface option.

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.

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.

lacp
    Uses the IEEE 802.3ad 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.

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) configuration file for netstart(8).

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

HISTORY
The trunk device first appeared in OpenBSD 3.8.

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) duplicate address detection (DAD) cannot properly deal with duplicate packets.

There is no way to configure LACP administrative variables, including system and port priorities. The current implementation always performs active-mode LACP and uses 0x8000 as system and port priorities.

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