We are in the process of replacing our firewall, which is currently the only thing connected to our Comcast Business Class modem. Comcast gives us 5 static IP addresses. Currently, all traffic to all 5 static IPs goes directly to the existing firewall.

Eventually, obviously all traffic will goto the new firewall, once the old firewall is removed from the network. But in the meantime, as we will have two firewalls plugged into the same Comcast modem, I need to route certain traffic to the new firewall instead of the old one. The firewall switchover is going to be slow and gradual as I am testing it, so I can't simply unplug the existing firewall and plug in the new one.

So my question is, how do I tell the modem to route all traffic that goes to a specific IP to goto the new firewall instead of the old one?

I've logged into the web interface for the modem, but the available options aren't very clear. There is a 1-to-1 NAT option (which I can't seem to get the interface for it to work properly) but I also see a "Static Routing" section. I always understood Static Routing to refer to routing data within the LAN though, so I'm not sure if that's what I'm looking for or not.

Keep in mind, I'm not looking to do simple port forwarding. I'm wanting 100% of traffic to certain public static IPs to go to the specified connected firewall (I'll deal with service policies there).

The modem is an SMC SMCD3G-CCR and is labeled as a Comcast Business Class Business IP Gateway. Any help or direction would be greatly appreciated.