[ubuntu] Understand bridged networking with KVM

I am a KVM-newbee and have a question about KVM and bridged networking for Ubuntu 12.04.

I am investigating how to setup a virtualized firewall, Sophos UTM 9 and has not fully understand how to configure the KVM-host bridged networking.

The KVM-host has three phsyical NICS:

• Internal - eth0
• Wireless - eth1
• External - eth2

Internal network
Network: 192.168.1.0/24
GW: 192.168.1.1 (UTM9 NIC IP-adress)

UTM9 is both DHCP-server and gateway for the Internal Network, has the static IP-adress 192.168.1.1. The KVM-host has a static IP-address on this network, 192.168.1.250

Wireless network
Network: 192.168.4.0/24
GW: 192.168.4.1 (UTM9 NIC IP-adress)

UTM9 is both DHCP-server and gateway for the Wireless Network, has the static IP-address 192.168.4.1
The KVM-host shall not have IP-connectivity on this network.

External network
Network 147.13.10.0/25
GW: 147.13.10.1 (ISP gateway)

UTM9 has a static IP-adresses on External, 147.13.10.2.
The KVM-host shall not have IP-connectivity on this network.

My question is how I shall setup bridged networking on the KVM-host? Can anyone give me an example how to configure /etc/networking/interfaces with bridged networking on the KVM-host according to above?



Cheers