VLAN(4)

VLAN(4) | Kernel Interfaces Manual | VLAN(4)

# NAME

vlan — IEEE 802.1Q Virtual LAN network device

# SYNOPSIS

pseudo-device vlan

# DESCRIPTION

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.

# EXAMPLES

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:

    create
    vlan 6 vlanif tlp0

# SEE ALSO

ifconfig(8)

# HISTORY

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

# BUGS

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

December 16, 2010 | NetBSD 7.0