VLANs are a way of virtually dividing up a network into many different subnetworks. Each will have its own broadcast domain and be isolated from the rest of the VLANs.

On FreeBSD, VLANs must be supported by the network card driver. To see which drivers support vlans, refer to the vlan(4) manual page.

When configuring a VLAN, a couple pieces of information must be known. First, which network interface? Second, what is the VLAN tag?

To configure VLANs at run time, with a NIC of em0 and a VLAN tag of 5. The command would look like this:

# ifconfig em0.5 create vlan 5 vlandev em0 inet 192.168.20.20/24

To configure VLANs at boot time, /etc/rc.conf must be updated. To duplicate the configuration above, the following will need to be added:

vlans_em0="5"
ifconfig_em0_5="inet 192.168.20.20/24"

Additional VLANs may be added, by simply adding the tag to the vlans_em0 field and adding an additional line configuring the network on that VLAN tag's interface.