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 1.8 2007/10/17 12:48:23 sephe 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 bce 4 , 97.Xr bge 4 , 98.Xr em 4 , 99.Xr gx 4 , 100.Xr nge 4 , 101.Xr re 4 , 102.Xr stge 4 , 103.Xr ti 4 , 104.Xr txp 4 , 105and 106.Xr vge 4 . 107.Pp 108The rest of the ethernet NICs supported by 109.Dx 110can run 111VLANs using software emulation in the 112.Nm 113driver. 114However, most of them lack the capability 115of transmitting and/or receiving oversized frames. 116Using such a NIC as a parent interface 117implies a reduced MTU on the corresponding 118.Nm 119interfaces. 120In the modern Internet, this is likely to cause 121.Xr tcp 4 122connectivity problems due to massive, inadequate 123.Xr icmp 4 124filtering that breaks the Path MTU Discovery mechanism. 125.Pp 126The NICs that support oversized frames are as follows: 127.Bl -tag -width ".Xr fxp 4 " -offset indent 128.It Xr dc 4 129supports long frames for 130.Nm 131natively. 132.It Xr de 4 133requires defining 134.Dv BIG_PACKET 135in the 136.Pa /sys/dev/netif/de/if_de.c 137source file and rebuilding the kernel. 138The hack works only for the 21041, 21140, and 21140A chips. 139.It Xr et 4 140supports long frames for 141.Nm 142natively. 143.It Xr fxp 4 144supports long frames for 145.Nm 146natively. 147.It Xr sis 4 148supports long frames for 149.Nm 150natively. 151.It Xr ste 4 152supports long frames for 153.Nm 154natively. 155.It Xr tl 4 156has support for long frames. 157.It Xr tx 4 158supports long frames for 159.Nm 160natively. 161.It Xr xl 4 162supports long frames only if the card is built on a newer chip 163(Cyclone and above). 164.El 165.Pp 166Note: 167Unless marked as having native support for 168.Nm , 169the above drivers don't inform the 170.Nm 171driver about their long frame handling capability. 172Just increase the MTU of a 173.Nm 174interface if it appears to be lower than 1500 bytes after 175attaching to a parent known to support long frames. 176.Sh SEE ALSO 177.Xr ifconfig 8 178.Sh BUGS 179No 802.1Q features except VLAN tagging are implemented. 180