.\"	$OpenBSD: trunk.4,v 1.31 2020/08/24 07:34:00 kn Exp $
.\"
.\" Copyright (c) 2005, 2006 Reyk Floeter <reyk@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: August 24 2020 $
.Dt TRUNK 4
.Os
.Sh NAME
.Nm trunk
.Nd link aggregation and link failover interface
.Sh SYNOPSIS
.Cd "pseudo-device trunk"
.Sh DESCRIPTION
The
.Nm
interface allows aggregation of multiple network interfaces as one virtual
.Nm
interface.
.Pp
A
.Nm
interface can be created using the
.Ic ifconfig trunk Ns Ar N Ic create
command.
.Pp
The driver currently supports the trunk protocols
.Ic broadcast ,
.Ic failover ,
.Ic lacp ,
.Ic loadbalance ,
.Ic none ,
and
.Ic 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.
.Bl -tag -width loadbalance
.It Ic broadcast
Sends frames to all ports of the trunk and receives frames on any
port of the trunk.
.It Ic 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.
.It Ic lacp
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.
.It Ic 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.
.It Ic none
This protocol is intended to do nothing: it disables any traffic without
disabling the
.Nm
interface itself.
.It Ic 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.
.El
.Pp
The configuration can be done at runtime or by setting up a
.Xr hostname.if 5
configuration file for
.Xr netstart 8 .
.Sh EXAMPLES
Create a simple round robin trunk with two
.Xr bge 4
Gigabit Ethernet
interfaces:
.Bd -literal -offset indent
# ifconfig bge0 up
# ifconfig bge1 up
# ifconfig trunk0 trunkport bge0 trunkport bge1 \e
	192.168.1.1 netmask 255.255.255.0
.Ed
.Pp
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:
.Bd -literal -offset indent
# ifconfig em0 up
# ifconfig ath0 nwid my_net up
# ifconfig trunk0 trunkproto failover trunkport em0 trunkport ath0 \e
	192.168.1.1 netmask 255.255.255.0
.Ed
.Sh SEE ALSO
.Xr inet 4 ,
.Xr hostname.if 5 ,
.Xr ifconfig 8 ,
.Xr netstart 8
.Sh HISTORY
The
.Nm
device first appeared in
.Ox 3.8 .
.Sh AUTHORS
The
.Nm
driver was written by
.An Reyk Floeter Aq Mt reyk@openbsd.org .
.Sh CAVEATS
The trunk protocols
.Ic loadbalance
and
.Ic roundrobin
require a switch which supports IEEE 802.3ad static link aggregation;
otherwise protocols
such as
.Xr inet6 4
duplicate address detection (DAD)
cannot properly deal with duplicate packets.
.Pp
The
.Nm
interface takes its MTU from the first
.Ic trunkport .
To avoid mismatches, adding a child interface with a different
MTU is not permitted.