142 lines
3.9 KiB
Groff
142 lines
3.9 KiB
Groff
.\"
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.\" Copyright (c) 2001 Yar Tikhiy
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 25, 2001
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.Dt VLAN 4
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.Os
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.Sh NAME
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.Nm vlan
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.Nd IEEE 802.1Q VLAN network interface
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.Sh SYNOPSIS
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.Cd device vlan
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.\"
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.Sh DESCRIPTION
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The
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.Nm
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driver demultiplexes frames tagged according to
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the IEEE 802.1Q standard into logical
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.Nm
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network interfaces, which allows routing/bridging between
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multiple VLANs through a single switch trunk port.
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.Pp
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To function, a
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.Nm
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interface must be assigned a parent interface and
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numeric VLAN tag using
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.Xr ifconfig 8 .
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A single parent can be assigned to multiple
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.Nm
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interfaces provided they have different tags.
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The parent interface is likely to be an ethernet card connected
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to a properly configured switch port.
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The VLAN tag should match one of those set up in the switched
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network.
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.Pp
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The
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.Nm
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driver supports physical devices that do
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the VLAN demultiplexing in firmware.
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The
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.Cm link0
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flag should be set on a
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.Nm
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interface
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.Pq Em not on its parent
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using
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.Xr ifconfig 8
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in that case to indicate that the hardware support for
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the 802.1Q VLANs is present in its parent.
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.\"
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.Ss "Selecting the Right Network Interface Card to Run VLANs Through"
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By now, the only NICs that have both hardware support and proper
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driver hooks for the 802.1Q VLAN technology in
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.Fx
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are
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.Xr nge 4 ,
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.Xr ti 4 ,
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and
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.Xr txp 4 .
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.Pp
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The rest of the ethernet NICs supported by
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.Fx
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can run
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VLANs using the software emulation in the
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.Nm
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driver.
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However, most of them lack the capability
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of transmitting and/or receiving oversized frames.
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Using such a NIC as a parent interface for a
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.Nm
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implies a reduced MTU on the corresponding
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.Nm
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interfaces.
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In the modern Internet, this is likely to cause
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.Xr tcp 4
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connectivity problems due to massive, inadequate
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.Xr icmp 4
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filtering that breaks the Path MTU Discovery mechanism.
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.Pp
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The NICs that support oversized frames are as follows:
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.Bl -tag -width ".Xr fxp 4 " -offset indent
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.It Xr de 4
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requires defining
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.Dv BIG_PACKET
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in the
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.Pa /usr/src/sys/pci/if_de.c
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source file and rebuilding the kernel
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or module.
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The hack works only for the 21041, 21140, and 21140A chips.
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.It Xr fxp 4
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supports long frames for the
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.Nm
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natively.
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.It Xr tl 4
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does support long frames.
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.It Xr tx 4
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may begin supporting long frames soon.
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.It Xr xl 4
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supports long frames only if the card is built on a newer chip
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(Cyclone and above).
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.El
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.Pp
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Note:
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Except for
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.Xr fxp 4 ,
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none of the above drivers inform the
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.Nm
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driver about their support for long frames.
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Just fix the MTU of a
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.Nm
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interface if it appears to be lower than 1500 bytes after
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attaching the
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.Nm
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to a parent interface that is known to support long frames.
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.Sh SEE ALSO
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.Xr ifconfig 8
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.Sh BUGS
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No 802.1Q features except VLAN tagging are implemented.
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