Found out that PfSense even when connected as a 2nd router in a double NAT situation still “finds” the correct public IP address.
I can’t really find in the manuals etc how this works, maybe I overlooked something?
Or does this just work in some simple way that I haven’t learned about yet?
This might help. In summary, you can tell pfSense to look at a specific place and expect a reply of what that host determines the IP is coming from for the incoming request. In theory, you could probably put an HTTP server up in between the two NAT layers and have pfSense look there, which should report the IP prior to leaving the second NAT layer. I think.
Thanks for pointing me in the right direction.