Whonix on bridged interface


My host is running ArchLinux which is configured to use a bridged network (br0). I run several other libvirt guests, with, for example, the following network configurations and DHCP:

<interface type="bridge">
  <mac address="gg:gg:gg:gg:gg:gg"/>
  <source bridge="br0"/>
  <target dev="vnet0"/>
  <model type="virtio"/>
  <alias name="net0"/>
  <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/>

I have followed the installation instructions to create the internal and external Whonix networks, but I have no connectivity. How can I make Whonix work on this machine?