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 January 30, 2005 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 miibus 36.Cd device vlan 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.Sh HARDWARE 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.Pp 91By now, the list of physical interfaces able of full VLAN processing 92in the hardware is limited to the following devices: 93.Xr bge 4 , 94.Xr em 4 , 95.Xr ixgb 4 , 96.Xr nge 4 , 97.Xr re 4 , 98.Xr ti 4 , 99.Xr txp 4 , 100and 101.Xr vge 4 . 102.Pp 103The rest of the Ethernet interfaces can run 104VLANs using software emulation in the 105.Nm 106driver. 107However, most of them lack the capability 108of transmitting and receiving oversized frames. 109Assigning such an interface as the parent to 110.Nm 111will result in a reduced MTU on the corresponding 112.Nm 113interfaces. 114In the modern Internet, this is likely to cause 115.Xr tcp 4 116connectivity problems due to massive, inadequate 117.Xr icmp 4 118filtering that breaks the Path MTU Discovery mechanism. 119.Pp 120The interfaces that support oversized frames are as follows: 121.Bl -tag -width ".Xr fxp 4 " -offset indent 122.It Xr bfe 4 123supports long frames for 124.Nm 125natively. 126.It Xr dc 4 127supports long frames for 128.Nm 129natively. 130.It Xr de 4 131requires defining 132.Dv BIG_PACKET 133in the 134.Pa /usr/src/sys/pci/if_de.c 135source file and rebuilding the kernel 136or module. 137The hack works only for the 21041, 21140, and 21140A chips. 138.It Xr fxp 4 139supports long frames for 140.Nm 141natively. 142.It Xr hme 4 143supports long frames for 144.Nm 145natively. 146.It Xr rl 4 147supports long frames for 148.Nm 149natively. 150.It Xr sis 4 151supports long frames for 152.Nm 153natively. 154.It Xr ste 4 155supports long frames for 156.Nm 157natively. 158.It Xr tl 4 159has support for long frames. 160.It Xr tx 4 161supports long frames for 162.Nm 163natively. 164.It Xr xl 4 165supports long frames only if the card is built on a newer chip 166(Cyclone and above). 167.El 168.Pp 169The 170.Nm 171driver automatically recognizes devices that natively support oversized frames 172for 173.Nm 174use and calculates the appropriate frame MTU based on the 175capabilities of the parent interface. 176The other interfaces listed above can handle oversized frames, 177but they do not advertise this ability of theirs. 178The MTU setting on 179.Nm 180can be corrected manually if used in conjunction with such parent interface. 181.Sh SEE ALSO 182.Xr kqueue 2 , 183.Xr miibus 4 , 184.Xr ifconfig 8 185.Sh BUGS 186No 802.1Q features except VLAN tagging are implemented. 187.Pp 188.Dv EVFILT_NETDEV 189events on a 190.Nm 191interface will be sent through 192.Xr kqueue 2 193only if the parent interface uses 194.Xr miibus 4 195for link state notification. 196