@lasergecko said in Second IP Address - Everything works except for one program/PF:
For some reason, it looks like pfSense is prohibiting just Dev from reaching the Prod FQDN, but just via that method.
The only one part where pfSense can affect the FQDN is at DNS resolution, if you use the DNS resolver. But since you say it resolves correctly, I cannot think of any issue with pfSense.
As I got you, the only problem is to access the dev server from within the same LAN. However, this traffic doesn't doesn't pass pfSense, when the host name resolves the the servers internal IP address.
So I think, you should look for the reason on the server itself. Maybe its firewall is blocking access from LAN, maybe the server have set a wrong network mask so that he is sending responses to the gateway.
Possibly you can sniff the traffic to find out more about what's going on.