I have just set up a router running pfSense on our network and forwarded the appropriate ports. I have a small web server running in my network, and a domain name pointing to our (WAN) IP. When accessing that domain name, everything works fine. However, when accessing a subdomain of the domain name, pfSense will give a DNS rebinding warning. This did not happen back when I used a DD-WRT router. What is the proper way to fix this? The DNS records for the subdomain also point to the same address (I use a virtual server to differentiate the subdomains.)
this is due to the fact that PF functions can't reflect in and out the same interface, it has to pass "through" the router so it redirects you to the warning. You can setup a .local domain or you can setup Split DNS in PFsense. Instructions for split DNS are in this PFsense KB article. I suggest split DNS to fix this.