apt-get install vlan
echo "8021q" >> /etc/modules
modprobe 8021q

The following example is for configuring a tagged vlan on eth0 ID 240

vconfig add eth0 240
ifconfig eth0.240 192.168.115.3 255.255.255.0

The following example is for configuring a tagged vlan on eth0 ID 240

/etc/network/interfaces

auto eth0.240
iface eth0.240 inet static
    address 192.168.115.3
    netmask 255.255.255.0
    vlan-raw-device eth0