Dual nic - one for snort, one for other

So, I've been running proxmox successfully for a few months now, and I really really like it.
Now I have come to the conclusion that I want to play a bit with snort and other IDS tools, and for that I want to dedicate one nic on my proxmox server to just that VM.So here's my physical setup
Internet -> WAN (pfsense) -> LAN (pfsense) -> Proxmox eth0 (set to vmbr0)
Mirrored port (pfsense) -> Proxmox eth1

I tried to just edit the /etc/network/interface file and add a duplicate information, just rename everything to vmbr1 and of course change the ip addresses.
When I did that I did not get any network at all for the proxmox server.

So basically the question is, how can I configure proxmox to use eth1 to my IDS-VM?

Thanks for the help