200 lines
5.3 KiB
Groff
200 lines
5.3 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 26, 2020
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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 line in your
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kernel configuration file:
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.Bd -ragged -offset indent
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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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.Nm
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initially assumes the same minimum length for tagged and untagged frames.
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This mode is selected by setting 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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to 0
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.Pq default .
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However, there are network devices that fail to adjust frame length
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when it falls 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 is 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 long frames (up to 1522 bytes including an Ethernet
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header and FCS).
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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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At present, these devices are capable of full VLAN processing
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in hardware:
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.Xr ae 4 ,
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.Xr age 4 ,
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.Xr alc 4 ,
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.Xr ale 4 ,
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.Xr bce 4 ,
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.Xr bge 4 ,
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.Xr bxe 4 ,
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.Xr cxgb 4 ,
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.Xr cxgbe 4 ,
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.Xr em 4 ,
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.Xr igb 4 ,
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.Xr ixgbe 4 ,
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.Xr jme 4 ,
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.Xr liquidio 4 ,
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.Xr msk 4 ,
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.Xr mxge 4 ,
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.Xr nge 4 ,
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.Xr re 4 ,
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.Xr sge 4 ,
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.Xr stge 4 ,
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.Xr ti 4 ,
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and
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.Xr vge 4 .
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.Pp
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Other Ethernet interfaces can run VLANs using software emulation in the
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.Nm
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driver.
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However, some lack the capability
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of transmitting and receiving long 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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These interfaces natively support long frames for
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.Nm :
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.Xr axe 4 ,
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.Xr bfe 4 ,
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.Xr cas 4 ,
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.Xr dc 4 ,
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.Xr et 4 ,
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.Xr fwe 4 ,
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.Xr fxp 4 ,
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.Xr gem 4 ,
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.Xr le 4 ,
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.Xr nfe 4 ,
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.Xr rl 4 ,
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.Xr sis 4 ,
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.Xr sk 4 ,
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.Xr ste 4 ,
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.Xr vr 4 ,
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.Xr vte 4 ,
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and
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.Xr xl 4 .
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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 long 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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Some other interfaces not listed above may handle long frames,
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but they do not advertise this ability.
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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 a parent interface.
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.Sh SEE ALSO
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.Xr ifconfig 8 ,
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.Xr sysctl 8
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