NATing for device without changing its IP?

I wanted to understand if its possible to set the WAN IP to match a device located on a LAN interface. This is simply to place a firewall in front of a single device (on a simple home network) for network auditing. There are no other devices behind the firewall.

I want to be able to do this "seamlessly" without changing the IP of the device. I understand I would have to add in portforwards for each port needed for access from WAN to the device.

Is this NAT config possible? Can I get some tips on how to do this correctly? primarily as it relates to routing.

I will need to then enable logging on the LAN interface for all traffic statefully originating from "LAN". So if that throws a wrench into the works, please let me know. I'm just starting to learn about iptables logging. I already have a syslog server that can receive logs from the FW, but haven't learned custom log rules yet.

TIA!

No, this is not possible. Routing does not work when the upstream and downstream networks are the same or overlapping. They must be unique and non-overlapping.

Perhaps what you need is to configure the device as a bridge, instead if a router. Or you can try with port mirroring on a switch.

I ended up just re-iping the device and moving its IP to the external WAN interface.