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VLAN(4)                    Kernel Interfaces Manual                    VLAN(4)

     vlan -- IEEE 802.1Q Virtual LAN network device

     pseudo-device vlan

     The vlan interface provides support for IEEE 802.1Q Virtual Local Area
     Networks (VLAN).  This supports the trunking of more than one network on
     a single network interface.  This is particularly useful on routers or on
     hosts which must be connected to many different networks through a single
     physical interface.

     To use a vlan interface, the administrator must first create the
     interface and then specify the VID (VLAN identifier, the first 12 bits
     from a 16-bit integer which distinguishes each VLAN from any others) and
     physical interface associated with the VLAN.  This can be done by using
     the ifconfig(8) create, vlan, and vlanif subcommands from a shell command
     line or script.  From within a C program, use the ioctl(2) system call
     with the SIOCSIFCREATE and SIOCSIFVLAN arguments.

     To be compatible with other IEEE 802.1Q devices, the vlan interface
     supports a 1500 byte MTU, which means that the parent interface will have
     to handle packets that are 4 bytes larger than the original Ethernet
     standard.  Drivers supporting this increased MTU are:

     -   drivers using the DP8390 core (such as ec(4), ne(4), we(4), and
         possibly others)
     -   bge(4)
     -   bnx(4)
     -   ea(4)
     -   eb(4)
     -   epic(4)
     -   etherip(4)
     -   ex(4)
     -   fxp(4)
     -   gem(4)
     -   hme(4)
     -   le(4)
     -   sip(4)
     -   ste(4)
     -   stge(4)
     -   ti(4)
     -   tl(4)
     -   tlp(4)
     -   vge(4)
     -   vr(4)
     -   wm(4)
     -   xi(4)

     vlan can be used with devices not supporting the IEEE 802.1Q MTU, but
     then the MTU of the vlan interface will be 4 bytes too small and will not
     interoperate properly with other IEEE 802.1Q devices, unless the MTU of
     the other hosts on the VLAN are also lowered to match.

     The following will create interface vlan0 with VID six, on the Ethernet
     interface tlp0:

           ifconfig vlan0 create
           ifconfig vlan0 vlan 6 vlanif tlp0

     After this set up, IP addresses (and/or other protocols) can be assigned
     to the vlan0 interface.  All other hosts on the Ethernet connected to
     tlp0 which configure a VLAN and use VID six will see all traffic
     transmitted through vlan0.

     The same VLAN can be created at system startup time by placing the
     following in /etc/ifconfig.vlan0:

           vlan 6 vlanif tlp0


     The vlan device first appeared in NetBSD 1.5.1, and was derived from a
     VLAN implementation that appeared in FreeBSD and OpenBSD.

     The vlan interfaces do not currently inherit changes made to the physical
     interfaces' MTU.

NetBSD 7.1.2                   December 16, 2010                  NetBSD 7.1.2