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.\" $FreeBSD$ 27.\" 28.Dd July 25, 2001 29.Dt VLAN 4 30.Os 31.Sh NAME 32.Nm vlan 33.Nd IEEE 802.1Q VLAN network interface 34.Sh SYNOPSIS 35.Cd device vlan 36.\" 37.Sh DESCRIPTION 38The 39.Nm 40driver demultiplexes frames tagged according to 41the IEEE 802.1Q standard into logical 42.Nm 43network interfaces, which allows routing/bridging between 44multiple VLANs through a single switch trunk port. 45.Pp 46Each 47.Nm 48interface is created at runtime using interface cloning. 49This is 50most easily done with the 51.Xr ifconfig 8 52.Cm create 53command or using the 54.Va cloned_interfaces 55variable in 56.Xr rc.conf 5 . 57.Pp 58To function, a 59.Nm 60interface must be assigned a parent interface and 61numeric VLAN tag using 62.Xr ifconfig 8 . 63A single parent can be assigned to multiple 64.Nm 65interfaces provided they have different tags. 66The parent interface is likely to be an ethernet card connected 67to a properly configured switch port. 68The VLAN tag should match one of those set up in the switched 69network. 70.Pp 71The 72.Nm 73driver supports physical devices that do 74the VLAN demultiplexing in firmware. 75The 76.Cm link0 77flag should be set on a 78.Nm 79interface 80.Pq Em not on its parent 81using 82.Xr ifconfig 8 83in that case to indicate that the hardware support for 84the 802.1Q VLANs is present in its parent. 85.\" 86.Ss "Selecting the Right Network Interface Card to Run VLANs Through" 87By now, the only NICs that have both hardware support and proper 88driver hooks for the 802.1Q VLAN technology in 89.Fx 90are 91.Xr bge 4 , 92.Xr nge 4 , 93.Xr ti 4 , 94and 95.Xr txp 4 . 96.Pp 97The rest of the ethernet NICs supported by 98.Fx 99can run 100VLANs using the software emulation in the 101.Nm 102driver. 103However, most of them lack the capability 104of transmitting and/or receiving oversized frames. 105Using such a NIC as a parent interface for a 106.Nm 107implies a reduced MTU on the corresponding 108.Nm 109interfaces. 110In the modern Internet, this is likely to cause 111.Xr tcp 4 112connectivity problems due to massive, inadequate 113.Xr icmp 4 114filtering that breaks the Path MTU Discovery mechanism. 115.Pp 116The NICs that support oversized frames are as follows: 117.Bl -tag -width ".Xr fxp 4 " -offset indent 118.It Xr dc 4 119supports long frames for the 120.Nm 121natively. 122.It Xr de 4 123requires defining 124.Dv BIG_PACKET 125in the 126.Pa /usr/src/sys/pci/if_de.c 127source file and rebuilding the kernel 128or module. 129The hack works only for the 21041, 21140, and 21140A chips. 130.It Xr fxp 4 131supports long frames for the 132.Nm 133natively. 134.It Xr sis 4 135supports long frames for the 136.Nm 137natively. 138.It Xr tl 4 139does support long frames. 140.It Xr tx 4 141does support long frames. 142.It Xr wx 4 143does support long frames. 144.It Xr xl 4 145supports long frames only if the card is built on a newer chip 146(Cyclone and above). 147.El 148.Pp 149Note: 150Except for 151.Xr fxp 4 , 152.Xr sis 4 153and 154.Xr tx 4 , 155none of the above drivers inform the 156.Nm 157driver about their support for long frames. 158Just fix the MTU of a 159.Nm 160interface if it appears to be lower than 1500 bytes after 161attaching the 162.Nm 163to a parent interface that is known to support long frames. 164.Sh SEE ALSO 165.Xr ifconfig 8 166.Sh BUGS 167No 802.1Q features except VLAN tagging are implemented. 168