Have a rather strange situation we are trying to solve, any suggestions would be appreciated.
The problem is our new ISP does not host static public IP’s on the WAN port. They want us to put our public IP’s on the LAN side of our router. So we will have 3 IP “groups”, within the MT1100AHx2.
Our “WAN” port will get a public IP through DHCP that is only for the ISP to route with. Then we have to create another IP group with our static public IP’s. Then our LAN port will have the 192.168.x.x private IP’s assigned. All hosted services are on private IP’s.
So what we are trying to do is get the private IP’s to NAT to the public IP’s, then route out on the WAN port without NATing to that address.
So all firewall/NAT functions happen between the private to public connection, then they must route out on the WAN port without NAT.
Incoming traffic will have our static public IP’s, the WAN port just needs to pass all incoming traffic to the public IP group, then it will get filtered/port mapped to private IP’s and go to the internal network on the LAN port.
I currently have ports 11 and 12 setup for the ISP connections.
eth1 is the private master and 2-5 are on the switch with it.
eth6 has the static public IP assigned, but nothing physically connected to it.
So outbound traffic will come in on eth1, be NATed to eth6, then go out on eth11or12. Incoming is the reverse. Does this make sense?
We have the LAN to WAN setup and working, just need to figure out how to get those static public IP addresses in the middle and working as our internet address. We just can’t come up with router logic that works.
Havnt tried this but my thoughts are: If the ISP is using DHCP to give you a connection then that ip would be a different network address to the one hes asking you to use for your public ip (different networks). Therefore i wouldnt be using a seperate NIC for the two networks, you can put both public (dhcp client IP) and public (yours) on the same interface and route between the two networks. So the firewall nat would be on your lan ip, the gatewayu for your lan would be your network address of your static public ip and then traffic is routed out to the dhcp public IP. 
The way I’ve always done this is use an empty bridge interface to “hold” the static IP assignments like a loopback interface on cisco/juniper and then setup your dst-nat from there, you can also then at that point setup masquerading on those IPs for outbound if you wanted as well.