31.11. VLANs

VLANs are a way of virtually dividing up a network into many different subnetworks, also referred to as segmenting. Each segment will have its own broadcast domain and be isolated from other VLANs.

在 FreeBSD 上,要使用 VLANs 必須有網路卡驅動程式的支援,要查看那些驅動程式支援 vlan,請參考 vlan(4) 操作手冊。

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


See how the interface name includes the NIC driver name and the VLAN tag, separated by a period? This is a best practice to make maintaining the VLAN configuration easy when many VLANs are present on a machine.

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


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.

It is useful to assign a symbolic name to an interface so that when the associated hardware is changed, only a few configuration variables need to be updated. For example, security cameras need to be run over VLAN 1 on em0. Later, if the em0 card is replaced with a card that uses the ixgb(4) driver, all references to em0.1 will not have to change to ixgb0.1.

To configure VLAN 5, on the NIC em0, assign the interface name cameras, and assign the interface an IP address of with a 24-bit prefix, use this command:

# ifconfig em0.5 create vlan 5 vlandev em0 name cameras inet

For an interface named video, use the following:

# ifconfig video.5 create vlan 5 vlandev video name cameras inet

To apply the changes at boot time, add the following lines to /etc/rc.conf:

create_args_camera="vlan 5"

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