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.\" $OpenBSD: vlan.4,v 1.1 2000/04/26 19:00:57 chris Exp $
.\"
.Dd 09 January 2000
.Dt VLAN 4
.Os
.Sh NAME
.Nm vlan
.Nd "IEEE 802.1Q encapsulation/decapsulation pseudo-device"
.Sh SYNOPSIS
.Cd pseudo-device vlan Op Ar count
.Sh DESCRIPTION
The
.Nm vlan
ethernet interface allows construction of virtual LANs when used in
conjunction with IEEE 802.1Q-compliant ethernet devices.
.Pp
This driver currently supports the following modes of operation:
.Bl -tag -width abc
.It 802.1Q encapsulation over ethernet (Ethernet protocol 0x8100)
Frame headers which normally contain the destination host, source host, and
protocol, are altered with additional information. After the source host,
a 32-bit 802.1Q header is included, with 16 bits for the ether type (0x8100), 3
bits for the priority field (not used in this implementation), 1 bit for
the canonical field (always 0), and 12 bits for the vlan identifier. Following
the vlan header is the actual ether type for the packet and length information.
.Pp
The 802.1Q header specifies the virtual LAN
and thus allows an ethernet switch or other 802.1Q compliant
network devices to be aware of which device the packet was intended for.
This driver allows OpenBSD to group packets logically with separate
interfaces.
.El
.Pp
The network interfaces are named
.Sy vlan Ns Ar 0 ,
.Sy vlan Ns Ar 1 ,
etc.
The number of interfaces is given by the corresponding
.Sy pseudo-device
line in the system config file.
.Xr vlan 4
interfaces support the following unique
.Xr ioctl 2 Ns s :
.Bl -tag -width aaa
.It SIOCSETVLAN:
Set the vlan tag and parent for a given vlan interface.
.It SIOCGETVLAN:
Get the vlan tag and parent for a given vlan interface.
.Pp
.El
The operation mode can be given as
.Bl -tag -width bbb
.It link0
The parent interface supports VLAN tagging/untagging in hardware,
this requires support from the ethernet driver as well.
.El
.Pp
to
.Xr ifconfig 8 .
.Pp
.Sh SEE ALSO
.Xr netintro 4 ,
.Xr ip 4 ,
.Xr bridge 4 ,
.Xr inet 4 ,
.Xr ifconfig 8
.Pp
A draft of IEEE 802.1Q standard can be obtained from
http://grouper.ieee.org/groups/802/1/pages/802.1Q.html
or the final version can be purchased from the
Institute of Electrical and Electronic Engineers, Inc.
.Sh BUGS
The 802.1Q specification allows for operation over FDDI and Token Ring
as well as Ethernet.
This driver only supports such operation with ethernet devices.
.Pp
Some ethernet chips (notably the Intel 82558/82559) automatically
discard frames that are larger then 1500 bytes. All ethernet
chips sporting this feature should allow for it to be turned off.
Optimally, upon loading, the chip's OpenBSD driver would do this.
A temporary kludge is to set the MTU for each machine behind each VLAN to
1496 or less. Refer to the hardware manual for your ethernet chip to determine
if it has this feature, and if so, for information on how to turn it off.
A symptom of this problem is that small packets (ICMP)
but packets which are >MTU size are dropped, thus causing
bulk TCP transfers to hang.
.Pp
Some ethernet chips support 802.1Q tagging/untagging in hardware, but
do not have the appropriate hooks in their driver to pass the packet
directly to if_vlan. The PCI device driver if_ti is able to do this,
use it as a reference.
.Pp
This driver could be extended to support the Cisco ISL VLAN protocol,
detailed at http://www.cisco.com/warp/public/741/4.html. Unfortunately,
public reimplementation of this protocol is currently prevented by patent
(at least in the USA).
.Pp
.Sh AUTHOR
Originally wollman@freebsd.org
|
