I'm trying to set up a multi-subnet network which will be largely on VMs, including the networking appliances but which will also have physical machines on it.

What I want to do is have two or more KVM/Qemu hosts with multiple NICs in them. The NICs will be donated to router/firewall VMs. For safety, I want to duplicate the critical VMs (both networking-related and other) across the wire to the other host, so I have failover of the entire VM. I would configure critical networking components such that the entire system is contained in each VM, so if one host goes down I'm still up.

I've never tried this on Linux-KVM. Is there somebody here who can make recommendations on how to proceed?