KVM bridge setup with three NICS?

Question

I'm a bit confused on how to setup a bridge for KVM on my Debian box that has three NICs in it. I've attached my current /etc/network/interface below. My goal here is to have a video surveillance server VM on the CAM LAN interface so I need just that interface bridged. I don't need the other two interfaces bridged.

Everything I'm seeing online deals with setting up a bridge using just one NIC. I can't seem to find anything that deals with multiple NICs on the same machine each having a different subnet. How would I go about bridging just the CAM LAN NIC and not breaking the networking already in place?

# The loopback network interface
auto lo
iface lo inet loopback

# Computer LAN
allow-hotplug enp3s0
iface enp3s0 inet static
    address 192.168.22.149
    netmask 255.255.255.0
    network 192.168.22.0
    broadcast 192.168.22.255
    gateway 192.168.22.1
    dns-nameservers 192.168.22.1 8.8.8.8

 # Cam LAN
 allow-hotplug enp1s0f1
 iface enp1s0f1 inet static
    address 192.168.2.50
    netmask 255.255.255.0
    post-up ip route add 192.168.2.0/24 dev enp1s0f1 src 192.168.2.50 table rt2
    post-up ip route add default via 192.168.2.1 dev enp1s0f1 table rt2
    post-up ip rule add from 192.168.2.50/32 table rt2
    post-up ip rule add to 192.168.2.50/32 table rt2

 # DMZ LAN
 allow-hotplug enp1s0f0
 iface enp1s0f0 inet static
    address 10.0.1.2
    netmask 255.255.255.0
    post-up ip route add 10.0.1.0/24 dev enp1s0f0 src 10.0.1.2 table rt3
    post-up ip route add default via 10.0.1.1 dev enp1s0f0 table rt3
    post-up ip rule add from 10.0.1.2/32 table rt3
    post-up ip rule add to 10.0.1.2/32 table rt3

Edit - So I have figured out how to manually add a bridge on the CLI. Its as follows:

# brctl addbr br0 # brctl addif br0 enp1s0f1 # ifconfig br0 up # dhclient br0

This successfully grabs an IP address on the CAM LAN interface from the upstream router which is correct. I can so assign a static (which is the ultimate end goal) with ifconfig br0 192.168.2.x netmask 255.255.255.0 up.

However, I can't figure out how to input this information into the /etc/network/interface file. I need the br0 bridge assigned to enp1s0f1 and I need them both to have static IPs.

Answer 1

Add a dummy interface. The reason is you want an interface with a fixed MAC address. The first interface that joins your bridge, gives the bridge it's MAC address (or the bridge adopts this MAC, however you want to read it).

auto virbr10-dummy
iface virbr10-dummy inet manual
pre-up /sbin/ip link add virbr10-dummy type dummy
up /sbin/ip link set virbr10-dummy address 52:54:00:f9:78:15

For KVM MAC addresses that don't clash, start them with 52:54:00

You then want to define your bridge

#Bridge definitions

auto virbr10 iface virbr10 inet static

bridge_ports virbr10-dummy

bridge_stp off

bridge_fd 0
address 192.168.2.50 netmask 255.255.255.0

gateway 192.168.2.1

post-up ip route add 192.168.2.x/32 via 192.168.2.1 #dev virbr10

Further info on jamielinux website but I have only just ported my configs from ubuntu18.04 to debian 10, so having trouble with the post-up routing part, and have temporarily put in a /etc/rc.local command until i work it out.