1.\" 2.\" Copyright (c) 2001 Yar Tikhiy 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/share/man/man4/vlan.4,v 1.1.2.6 2002/08/30 11:53:56 yar Exp $ 27.\" $DragonFly: src/share/man/man4/vlan.4,v 1.5 2005/12/30 17:41:15 dillon Exp $ 28.\" 29.Dd July 25, 2001 30.Dt VLAN 4 31.Os 32.Sh NAME 33.Nm vlan 34.Nd IEEE 802.1Q VLAN network interface 35.Sh SYNOPSIS 36.Cd pseudo-device vlan Op Ar count 37.\" 38.Sh DESCRIPTION 39The 40.Nm 41driver demultiplexes frames tagged according to 42the IEEE 802.1Q standard into logical 43.Nm 44network interfaces, which allows routing/bridging between 45multiple VLANs through a single switch trunk port. 46.Pp 47Each 48.Nm 49interface is created at runtime using interface cloning. 50This is 51most easily done with the 52.Xr ifconfig 8 53.Cm create 54command or using the 55.Va cloned_interfaces 56variable in 57.Xr rc.conf 5 . 58.Pp 59To function, a 60.Nm 61interface must be assigned a parent interface and 62numeric VLAN tag using 63.Xr ifconfig 8 . 64A single parent can be assigned to multiple 65.Nm 66interfaces provided they have different tags. 67The parent interface is likely to be an ethernet card connected 68to a properly configured switch port. 69The VLAN tag should match one of those set up in the switched 70network. 71.Pp 72The 73.Nm 74driver supports efficient operation over parent interfaces that can provide 75help in processing VLANs. 76Such interfaces are automatically recognized by their capabilities. 77Depending on the level of sophistication found in a physical 78interface, it may do full VLAN processing or just be able to 79receive and transmit frames exceeding the maximum Ethernet frame size 80by the length of a 802.1Q header. 81The capabilities may be user-controlled by the respective parameters to 82.Xr ifconfig 8 , 83.Cm vlanhwtag 84and 85.Cm vlanmtu . 86However, a physical interface is not obliged to react to them: 87It may have either capability enabled permanently without 88a way to turn it off. 89The whole issue is very specific to a particular device and its driver. 90.\" 91.Ss "Selecting the Right Network Interface Card to Run VLANs Through" 92By now, the only NICs that have both hardware support and proper 93driver hooks for the 802.1Q VLAN technology in 94.Dx 95are 96.Xr bge 4 , 97.Xr em 4 , 98.Xr gx 4 , 99.Xr nge 4 , 100.Xr re 4 , 101.Xr ti 4 , 102and 103.Xr txp 4 . 104.Pp 105The rest of the ethernet NICs supported by 106.Dx 107can run 108VLANs using software emulation in the 109.Nm 110driver. 111However, most of them lack the capability 112of transmitting and/or receiving oversized frames. 113Using such a NIC as a parent interface 114implies a reduced MTU on the corresponding 115.Nm 116interfaces. 117In the modern Internet, this is likely to cause 118.Xr tcp 4 119connectivity problems due to massive, inadequate 120.Xr icmp 4 121filtering that breaks the Path MTU Discovery mechanism. 122.Pp 123The NICs that support oversized frames are as follows: 124.Bl -tag -width ".Xr fxp 4 " -offset indent 125.It Xr dc 4 126supports long frames for 127.Nm 128natively. 129.It Xr de 4 130requires defining 131.Dv BIG_PACKET 132in the 133.Pa /sys/dev/netif/de/if_de.c 134source file and rebuilding the kernel. 135The hack works only for the 21041, 21140, and 21140A chips. 136.It Xr fxp 4 137supports long frames for 138.Nm 139natively. 140.It Xr sis 4 141supports long frames for 142.Nm 143natively. 144.It Xr ste 4 145supports long frames for 146.Nm 147natively. 148.It Xr tl 4 149has support for long frames. 150.It Xr tx 4 151supports long frames for 152.Nm 153natively. 154.It Xr xl 4 155supports long frames only if the card is built on a newer chip 156(Cyclone and above). 157.El 158.Pp 159Note: 160Unless marked as having native support for 161.Nm , 162the above drivers don't inform the 163.Nm 164driver about their long frame handling capability. 165Just increase the MTU of a 166.Nm 167interface if it appears to be lower than 1500 bytes after 168attaching to a parent known to support long frames. 169.Sh SEE ALSO 170.Xr ifconfig 8 171.Sh BUGS 172No 802.1Q features except VLAN tagging are implemented. 173