TRUNK(4) BSD Kernel Interfaces Manual TRUNK(4)
trunk -- link aggregation and link failover interface
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 com-
mand. 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
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 spe-
cific 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 pro-
tocol 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).
Create a simple round robin trunk with two bge(4) Gigabit Ethernet inter-
# 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
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 <email@example.com>.
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
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 permit-
BSD March 28, 2017 BSD