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VLAN(4) NetBSD Kernel Interfaces Manual VLAN(4)
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by Kimmo Suominen.
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vlan -- IEEE 802.1Q Virtual LAN network device
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
To use a vlan interface, the administrator must first create the inter-
face and then specify the VID (VLAN identifier, the first 12 bits from a
16-bit integer which distinguishes each VLAN from any others) and physi-
cal 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 sup-
ports a 1500 byte MTU, which means that the parent interface will have to
handle packets that are 4 bytes larger than the original Ethernet stan-
dard. Drivers supporting this increased MTU are:
- drivers using the DP8390 core (such as ec(4), ne(4), we(4), and
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
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 trans-
mitted through vlan0.
The same VLAN can be created at system startup time by placing the fol-
lowing 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
NetBSD 5.0 November 15, 2008 NetBSD 5.0