Ubuntu, VLANs and Bridges

Bridge and VLAN support has improved dramatically under Ubuntu and probably Debian as well since I last looked into it. once upon a time to create a bridge linked to a VLAN interface you would have to do horrible things like.

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auto eth0
ifconfig eth0 inet manual
    pre-up /sbin/vconfig set_name_type VLAN_PLUS_VID_NO_PAD || true

auto vlan7
iface vlan7 inet manual
    pre-up /sbin/vconfig add eth0 7 || true
    post-down /sbin/vconfig rem vlan7 || true

auto br0
    pre-up brctl addbr br0
    pre-up brctl addif br0 vlan7
    post-down brctl delbr br0
    address 10.38.38.1
    netmask 255.255.255.0
    network 10.38.38.0
    broadcast 10.38.38.255

Now the bridge-utils and vlan packages provide hooks into the ifup and ifdown commands so you can simply do

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auto br-vlan4
iface br-vlan4 inet static
    address 10.38.38.1
    netmask 255.255.255.0
    network 10.38.38.0
    broadcast 10.38.38.255
    vlan-raw-device eth1
    bridge_ports vlan4
    bridge_maxwait 0
    bridge_fd 0
    bridge_stp off

Which will automagically

Bring up eth1
Create vlan4 bound to the eth1 interface
Bring up vlan4
Create the br0 with vlan4 attached
Give eth1 the same HW address as br0
Bring up br0 with the IP address

Nifty!

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