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.Dd December 26, 2020 27.Dt VLAN 4 28.Os 29.Sh NAME 30.Nm vlan 31.Nd "IEEE 802.1Q VLAN network interface" 32.Sh SYNOPSIS 33To compile this driver into the kernel, 34place the following line in your 35kernel configuration file: 36.Bd -ragged -offset indent 37.Cd "device vlan" 38.Ed 39.Pp 40Alternatively, to load the driver as a 41module at boot time, place the following line in 42.Xr loader.conf 5 : 43.Bd -literal -offset indent 44if_vlan_load="YES" 45.Ed 46.Sh DESCRIPTION 47The 48.Nm 49driver demultiplexes frames tagged according to 50the IEEE 802.1Q standard into logical 51.Nm 52network interfaces, which allows routing/bridging between 53multiple VLANs through a single switch trunk port. 54.Pp 55Each 56.Nm 57interface is created at runtime using interface cloning. 58This is 59most easily done with the 60.Xr ifconfig 8 61.Cm create 62command or using the 63.Va cloned_interfaces 64variable in 65.Xr rc.conf 5 . 66.Pp 67To function, a 68.Nm 69interface must be assigned a parent interface and 70numeric VLAN tag using 71.Xr ifconfig 8 . 72A single parent can be assigned to multiple 73.Nm 74interfaces provided they have different tags. 75The parent interface is likely to be an Ethernet card connected 76to a properly configured switch port. 77The VLAN tag should match one of those set up in the switched 78network. 79.Pp 80.Nm 81initially assumes the same minimum length for tagged and untagged frames. 82This mode is selected by setting the 83.Xr sysctl 8 84variable 85.Va net.link.vlan.soft_pad 86to 0 87.Pq default . 88However, there are network devices that fail to adjust frame length 89when it falls below the allowed minimum due to untagging. 90Such devices should be able to interoperate with 91.Nm 92after changing the value of 93.Va net.link.vlan.soft_pad 94to 1. 95In the latter mode, 96.Nm 97will pad short frames before tagging them 98so that their length is not less than the minimum value 99after untagging by the non-compliant devices. 100.Sh HARDWARE 101The 102.Nm 103driver supports efficient operation over parent interfaces that can provide 104help in processing VLANs. 105Such interfaces are automatically recognized by their capabilities. 106Depending on the level of sophistication found in a physical 107interface, it may do full VLAN processing or just be able to 108receive and transmit long frames (up to 1522 bytes including an Ethernet 109header and FCS). 110The capabilities may be user-controlled by the respective parameters to 111.Xr ifconfig 8 , 112.Cm vlanhwtag , 113and 114.Cm vlanmtu . 115However, a physical interface is not obliged to react to them: 116It may have either capability enabled permanently without 117a way to turn it off. 118The whole issue is very specific to a particular device and its driver. 119.Pp 120At present, these devices are capable of full VLAN processing 121in hardware: 122.Xr ae 4 , 123.Xr age 4 , 124.Xr alc 4 , 125.Xr ale 4 , 126.Xr bce 4 , 127.Xr bge 4 , 128.Xr bxe 4 , 129.Xr cxgb 4 , 130.Xr cxgbe 4 , 131.Xr em 4 , 132.Xr igb 4 , 133.Xr ix 4 , 134.Xr jme 4 , 135.Xr liquidio 4 , 136.Xr msk 4 , 137.Xr mxge 4 , 138.Xr nge 4 , 139.Xr re 4 , 140.Xr sge 4 , 141.Xr stge 4 , 142.Xr ti 4 , 143and 144.Xr vge 4 . 145.Pp 146Other Ethernet interfaces can run VLANs using software emulation in the 147.Nm 148driver. 149However, some lack the capability 150of transmitting and receiving long frames. 151Assigning such an interface as the parent to 152.Nm 153will result in a reduced MTU on the corresponding 154.Nm 155interfaces. 156In the modern Internet, this is likely to cause 157.Xr tcp 4 158connectivity problems due to massive, inadequate 159.Xr icmp 4 160filtering that breaks the Path MTU Discovery mechanism. 161.Pp 162These interfaces natively support long frames for 163.Nm : 164.Xr axe 4 , 165.Xr bfe 4 , 166.Xr cas 4 , 167.Xr dc 4 , 168.Xr et 4 , 169.Xr fwe 4 , 170.Xr fxp 4 , 171.Xr gem 4 , 172.Xr le 4 , 173.Xr nfe 4 , 174.Xr rl 4 , 175.Xr sis 4 , 176.Xr sk 4 , 177.Xr ste 4 , 178.Xr vr 4 , 179.Xr vte 4 , 180and 181.Xr xl 4 . 182.Pp 183The 184.Nm 185driver automatically recognizes devices that natively support long frames 186for 187.Nm 188use and calculates the appropriate frame MTU based on the 189capabilities of the parent interface. 190Some other interfaces not listed above may handle long frames, 191but they do not advertise this ability. 192The MTU setting on 193.Nm 194can be corrected manually if used in conjunction with such a parent interface. 195.Sh SEE ALSO 196.Xr ifconfig 8 , 197.Xr sysctl 8 198