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.