.\" $OpenBSD: vlan.4,v 1.41 2015/01/15 20:37:36 schwarze Exp $
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.\" by Jason R. Thorpe of Zembu Labs, Inc.
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.Dd $Mdocdate: January 15 2015 $
.Dt VLAN 4
.Os
.Sh NAME
.Nm vlan ,
.Nm svlan
.Nd IEEE 802.1Q/1AD pseudo-device
.Sh SYNOPSIS
.Cd "pseudo-device vlan"
.Sh DESCRIPTION
The
.Nm
Ethernet interface allows construction of virtual LANs when used in
conjunction with IEEE 802.1Q-compliant Ethernet devices.
The
.Nm svlan
Ethernet interface allows construction of IEEE 802.1AD-compliant
provider bridges.
It is normally used for QinQ to stack
.Nm
interfaces on top of it.
.Pp
The interfaces can be created at runtime using the
.Ic ifconfig vlan Ns Ar N Ic create
command or by setting up a
.Xr hostname.if 5
configuration file for
.Xr netstart 8 .
The interface itself can be configured with
.Xr ifconfig 8 ;
see its manual page for more information.
.Pp
For
.Nm
devices,
the 802.1Q header specifies the virtual LAN number, and thus allows an
Ethernet switch (or other 802.1Q compliant network devices) to be aware of
which LAN the frame is part of, and in the case of a switch, which
port(s) the frame can go to.
Frames transmitted through the vlan interface will be diverted to the specified
physical interface with a 802.1Q vlan tag added.
802.1Q frames received by the parent interface with the
correct vlan tag will be diverted to the associated
.Nm
pseudo-interface.
.Pp
Frame headers which normally contain the destination host, source host, and
protocol, are altered with additional information, comprising as follows:
16 bits for the ether type (0x8100);
3 bits for the priority field;
1 bit for the canonical field (always 0);
and 12 bits for the vlan identifier.
The priority field may be altered via
.Xr pf.conf 5 ;
see the
.Cm prio
option for more information.
Following the vlan header is the actual ether type for the frame and length
information.
.Pp
For
.Nm svlan
devices,
the configuration is identical to the
.Nm
interface, the only differences being that it uses a different Ethernet
type (0x88a8) and an independent VLAN ID space on the parent
interface.
.Pp
.Nm
and
.Nm svlan
interfaces support the following unique
.Xr ioctl 2 Ns s :
.Bl -tag -width "SIOCSETVLAN" -offset 3n
.It SIOCGETVLAN
Get the vlan tag and parent for a given vlan interface.
.It SIOCSETVLAN
Set the vlan tag and parent for a given vlan interface.
.El
.Pp
.Nm
and
.Nm svlan
interfaces use the following interface capabilities:
.Bl -tag -width "IFCAP_VLAN_HWTAGGING" -offset 3n
.It IFCAP_VLAN_MTU
The parent interface can handle full sized frames, plus the size
of the vlan tag.
.It IFCAP_VLAN_HWTAGGING
The parent interface will participate in the tagging of frames.
(This is not supported by
.Nm svlan
interfaces.)
.El
.Sh DIAGNOSTICS
.Bl -diag
.It "vlan0: initialized with non-standard mtu N (parent ...)"
The IFCAP_VLAN_MTU capability was not set on the parent interface.
We assume in this event that the parent interface is not capable of handling
frames larger than its MTU.
This will generally result in a non-compliant 802.1Q implementation.
.Pp
Some Ethernet chips will either discard or truncate
Ethernet frames that are larger than 1514 bytes.
This causes a problem as 802.1Q tagged frames can be up to 1518 bytes.
Most controller chips can be told not to discard large frames
and/or to increase the allowed frame size.
Refer to the hardware manual for your chip to do this.
.El
.Pp
If the IFCAP_VLAN_MTU capability is set on a vlan parent,
.Nm
assumes that the Ethernet chip on the parent can handle
oversized frames.
Either the chip allows 1518 byte frames by default (such as
.Xr rl 4 ) ,
the driver has instructed the chip to do so (such as
.Xr fxp 4
and
.Xr dc 4 ) ,
or the driver also takes advantage of a hardware tagging capability,
and thus oversized frames are never actually sent by
.Ox
(such as
.Xr txp 4
and
.Xr ti 4 ) .
.Sh SEE ALSO
.Xr bridge 4 ,
.Xr inet 4 ,
.Xr ip 4 ,
.Xr netintro 4 ,
.Xr hostname.if 5 ,
.Xr pf.conf 5 ,
.Xr ifconfig 8 ,
.Xr netstart 8
.Rs
.%T IEEE 802.1Q standard
.%U http://standards.ieee.org/getieee802/802.1.html
.Re
.Rs
.%Q Provider Bridges, QinQ
.%T IEEE 802.1AD standard
.Re
.Sh AUTHORS
Originally
.An Garrett Wollman Aq Mt wollman@freebsd.org .