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 December 26, 2020 29.Dt VLAN 4 30.Os 31.Sh NAME 32.Nm vlan 33.Nd "IEEE 802.1Q VLAN network interface" 34.Sh SYNOPSIS 35To compile this driver into the kernel, 36place the following line in your 37kernel configuration file: 38.Bd -ragged -offset indent 39.Cd "device vlan" 40.Ed 41.Pp 42Alternatively, to load the driver as a 43module at boot time, place the following line in 44.Xr loader.conf 5 : 45.Bd -literal -offset indent 46if_vlan_load="YES" 47.Ed 48.Sh DESCRIPTION 49The 50.Nm 51driver demultiplexes frames tagged according to 52the IEEE 802.1Q standard into logical 53.Nm 54network interfaces, which allows routing/bridging between 55multiple VLANs through a single switch trunk port. 56.Pp 57Each 58.Nm 59interface is created at runtime using interface cloning. 60This is 61most easily done with the 62.Xr ifconfig 8 63.Cm create 64command or using the 65.Va cloned_interfaces 66variable in 67.Xr rc.conf 5 . 68.Pp 69To function, a 70.Nm 71interface must be assigned a parent interface and 72numeric VLAN tag using 73.Xr ifconfig 8 . 74A single parent can be assigned to multiple 75.Nm 76interfaces provided they have different tags. 77The parent interface is likely to be an Ethernet card connected 78to a properly configured switch port. 79The VLAN tag should match one of those set up in the switched 80network. 81.Pp 82.Nm 83initially assumes the same minimum length for tagged and untagged frames. 84This mode is selected by setting the 85.Xr sysctl 8 86variable 87.Va net.link.vlan.soft_pad 88to 0 89.Pq default . 90However, there are network devices that fail to adjust frame length 91when it falls below the allowed minimum due to untagging. 92Such devices should be able to interoperate with 93.Nm 94after changing the value of 95.Va net.link.vlan.soft_pad 96to 1. 97In the latter mode, 98.Nm 99will pad short frames before tagging them 100so that their length is not less than the minimum value 101after untagging by the non-compliant devices. 102.Sh HARDWARE 103The 104.Nm 105driver supports efficient operation over parent interfaces that can provide 106help in processing VLANs. 107Such interfaces are automatically recognized by their capabilities. 108Depending on the level of sophistication found in a physical 109interface, it may do full VLAN processing or just be able to 110receive and transmit long frames (up to 1522 bytes including an Ethernet 111header and FCS). 112The capabilities may be user-controlled by the respective parameters to 113.Xr ifconfig 8 , 114.Cm vlanhwtag , 115and 116.Cm vlanmtu . 117However, a physical interface is not obliged to react to them: 118It may have either capability enabled permanently without 119a way to turn it off. 120The whole issue is very specific to a particular device and its driver. 121.Pp 122At present, these devices are capable of full VLAN processing 123in hardware: 124.Xr ae 4 , 125.Xr age 4 , 126.Xr alc 4 , 127.Xr ale 4 , 128.Xr bce 4 , 129.Xr bge 4 , 130.Xr bxe 4 , 131.Xr cxgb 4 , 132.Xr cxgbe 4 , 133.Xr em 4 , 134.Xr igb 4 , 135.Xr ixgbe 4 , 136.Xr jme 4 , 137.Xr liquidio 4 , 138.Xr msk 4 , 139.Xr mxge 4 , 140.Xr nge 4 , 141.Xr re 4 , 142.Xr sge 4 , 143.Xr stge 4 , 144.Xr ti 4 , 145and 146.Xr vge 4 . 147.Pp 148Other Ethernet interfaces can run VLANs using software emulation in the 149.Nm 150driver. 151However, some lack the capability 152of transmitting and receiving long frames. 153Assigning such an interface as the parent to 154.Nm 155will result in a reduced MTU on the corresponding 156.Nm 157interfaces. 158In the modern Internet, this is likely to cause 159.Xr tcp 4 160connectivity problems due to massive, inadequate 161.Xr icmp 4 162filtering that breaks the Path MTU Discovery mechanism. 163.Pp 164These interfaces natively support long frames for 165.Nm : 166.Xr axe 4 , 167.Xr bfe 4 , 168.Xr cas 4 , 169.Xr dc 4 , 170.Xr et 4 , 171.Xr fwe 4 , 172.Xr fxp 4 , 173.Xr gem 4 , 174.Xr le 4 , 175.Xr nfe 4 , 176.Xr rl 4 , 177.Xr sis 4 , 178.Xr sk 4 , 179.Xr ste 4 , 180.Xr vr 4 , 181.Xr vte 4 , 182and 183.Xr xl 4 . 184.Pp 185The 186.Nm 187driver automatically recognizes devices that natively support long frames 188for 189.Nm 190use and calculates the appropriate frame MTU based on the 191capabilities of the parent interface. 192Some other interfaces not listed above may handle long frames, 193but they do not advertise this ability. 194The MTU setting on 195.Nm 196can be corrected manually if used in conjunction with such a parent interface. 197.Sh SEE ALSO 198.Xr ifconfig 8 , 199.Xr sysctl 8 200