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 46To function, a 47.Nm 48interface must be assigned a parent interface and 49numeric VLAN tag using 50.Xr ifconfig 8 . 51A single parent can be assigned to multiple 52.Nm 53interfaces provided they have different tags. 54The parent interface is likely to be an ethernet card connected 55to a properly configured switch port. 56The VLAN tag should match one of those set up in the switched 57network. 58.Pp 59The 60.Nm 61driver supports physical devices that do 62the VLAN demultiplexing in firmware. 63The 64.Cm link0 65flag should be set on a 66.Nm 67interface 68.Pq Em not on its parent 69using 70.Xr ifconfig 8 71in that case to indicate that the hardware support for 72the 802.1Q VLANs is present in its parent. 73.\" 74.Ss "Selecting the Right Network Interface Card to Run VLANs Through" 75By now, the only NICs that have both hardware support and proper 76driver hooks for the 802.1Q VLAN technology in 77.Fx 78are 79.Xr bge 4 , 80.Xr nge 4 , 81.Xr ti 4 , 82and 83.Xr txp 4 . 84.Pp 85The rest of the ethernet NICs supported by 86.Fx 87can run 88VLANs using the software emulation in the 89.Nm 90driver. 91However, most of them lack the capability 92of transmitting and/or receiving oversized frames. 93Using such a NIC as a parent interface for a 94.Nm 95implies a reduced MTU on the corresponding 96.Nm 97interfaces. 98In the modern Internet, this is likely to cause 99.Xr tcp 4 100connectivity problems due to massive, inadequate 101.Xr icmp 4 102filtering that breaks the Path MTU Discovery mechanism. 103.Pp 104The NICs that support oversized frames are as follows: 105.Bl -tag -width ".Xr fxp 4 " -offset indent 106.It Xr de 4 107requires defining 108.Dv BIG_PACKET 109in the 110.Pa /usr/src/sys/pci/if_de.c 111source file and rebuilding the kernel 112or module. 113The hack works only for the 21041, 21140, and 21140A chips. 114.It Xr fxp 4 115supports long frames for the 116.Nm 117natively. 118.It Xr tl 4 119does support long frames. 120.It Xr tx 4 121does support long frames. 122.It Xr wx 4 123does support long frames. 124.It Xr xl 4 125supports long frames only if the card is built on a newer chip 126(Cyclone and above). 127.El 128.Pp 129Note: 130Except for 131.Xr fxp 4 132and 133.Xr tx 4 , 134none of the above drivers inform the 135.Nm 136driver about their support for long frames. 137Just fix the MTU of a 138.Nm 139interface if it appears to be lower than 1500 bytes after 140attaching the 141.Nm 142to a parent interface that is known to support long frames. 143.Sh SEE ALSO 144.Xr ifconfig 8 145.Sh BUGS 146No 802.1Q features except VLAN tagging are implemented. 147