243 lines
6.3 KiB
Groff
243 lines
6.3 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 December 13, 2006
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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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To compile this driver into the kernel,
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place the following lines in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device miibus"
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.Cd "device vlan"
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.Ed
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.Pp
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Alternatively, to load the driver as a
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module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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if_vlan_load="YES"
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.Ed
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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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Each
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.Nm
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interface is created at runtime using interface cloning.
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This is
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most easily done with the
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.Xr ifconfig 8
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.Cm create
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command or using the
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.Va cloned_interfaces
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variable in
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.Xr rc.conf 5 .
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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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Initially
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.Nm
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assumes the same minimum length for tagged and untagged frames.
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This mode is selected by the
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.Xr sysctl 8
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variable
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.Va net.link.vlan.soft_pad
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set to 0 (default).
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However, there are network devices that fail to adjust frame length,
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should it fall below the allowed minimum due to untagging.
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Such devices should be able to interoperate with
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.Nm
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after changing the value of
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.Va net.link.vlan.soft_pad
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to 1.
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In the latter mode,
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.Nm
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will pad short frames before tagging them
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so that their length stays not less than the minimum value
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after untagging by the non-compliant devices.
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.Sh HARDWARE
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The
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.Nm
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driver supports efficient operation over parent interfaces that can provide
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help in processing VLANs.
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Such interfaces are automatically recognized by their capabilities.
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Depending on the level of sophistication found in a physical
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interface, it may do full VLAN processing or just be able to
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receive and transmit frames exceeding the maximum Ethernet frame size
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by the length of a 802.1Q header.
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The capabilities may be user-controlled by the respective parameters to
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.Xr ifconfig 8 ,
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.Cm vlanhwtag
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and
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.Cm vlanmtu .
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However, a physical interface is not obliged to react to them:
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It may have either capability enabled permanently without
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a way to turn it off.
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The whole issue is very specific to a particular device and its driver.
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.Pp
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By now, the list of physical interfaces able of full VLAN processing
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in the hardware is limited to the following devices:
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.Xr bge 4 ,
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.Xr em 4 ,
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.Xr ixgb 4 ,
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.Xr msk 4 ,
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.Xr nge 4 ,
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.Xr re 4 ,
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.Xr stge 4 ,
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.Xr ti 4 ,
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.Xr txp 4 ,
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and
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.Xr vge 4 .
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.Pp
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The rest of the Ethernet interfaces can run
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VLANs using 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 receiving oversized frames.
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Assigning such an interface as the parent to
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.Nm
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will result in 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 interfaces 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 bfe 4
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supports long frames for
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.Nm
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natively.
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.It Xr dc 4
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supports long frames for
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.Nm
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natively.
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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
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.Nm
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natively.
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.It Xr gem 4
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supports long frames for
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.Nm
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natively.
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.It Xr hme 4
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supports long frames for
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.Nm
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natively.
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.It Xr le 4
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supports long frames for
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.Nm
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natively.
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.It Xr rl 4
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supports long frames for
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.Nm
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natively.
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.It Xr sis 4
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supports long frames for
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.Nm
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natively.
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.It Xr sk 4
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supports long frames for
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.Nm
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natively.
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.It Xr ste 4
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supports long frames for
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.Nm
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natively.
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.It Xr tl 4
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has support for long frames.
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.It Xr tx 4
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supports long frames for
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.Nm
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natively.
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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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The
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.Nm
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driver automatically recognizes devices that natively support oversized frames
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for
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.Nm
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use and calculates the appropriate frame MTU based on the
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capabilities of the parent interface.
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The other interfaces listed above can handle oversized frames,
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but they do not advertise this ability of theirs.
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The MTU setting on
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.Nm
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can be corrected manually if used in conjunction with such parent interface.
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.Sh SEE ALSO
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.Xr kqueue 2 ,
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.Xr miibus 4 ,
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.Xr ifconfig 8 ,
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.Xr sysctl 8
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.Sh BUGS
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No 802.1Q features except VLAN tagging are implemented.
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.Pp
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.Dv EVFILT_NETDEV
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events on a
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.Nm
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interface will be sent through
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.Xr kqueue 2
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only if the parent interface uses
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.Xr miibus 4
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for link state notification.
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