How to set the interface uses only for forwarding on the VM router?

Have a network diagram is shown in the picture:

Explanation:

1. "Server1" has 2 network interface "NIC1" and "NIC2".
   
2. On Server1 raised "VM1" from virtualbox, which is installed on pfsense is also (a software router\proxy\firewall)
   
3. On "VM1" configured with 2 network interface bridge for each physical NIC s Server1.
   
4. In NIC1 the cable comes from the ISP with an external IP address
   
5. NIC2 is used as a LAN interface and receives settings from pfsense is also on VM1, which raised DNS/DHCP.
   
   
   

What it takes: I need to get on Server1 NIC1 were used ONLY for prokidyvaya traffic to VM1 to ultimately the ability to learn the standard scheme WAN <---> firewall<--->LAN, where Server1 is the host LAN network.
Otherwise I have 2 look out of the node (Server1 and VM1).
How to implement it?