If you are encountering the “Plex is not available outside your network” message, even after successfully opening the necessary ports, the underlying issue may be caused by the default configuration settings in OPNSense or pfSense. This is because, by default, they are configured to block DNS rebinding, a security measure to protect against common DNS rebinding attacks.
To solve this issue, we just have to mark the domain as a private domain in the DNS Service
OPNSense
Log into your OPNSense web interface.
Navigate to Services → Unbound DNS → Advanced
Add the following in the Private Domains field, then Save and apply the changes
plex.directpfSense
Log into your pfSense web interface.
Navigate to Services → DNS Resolver → General Settings
Add the following in the Other Settings field, then Save and apply the changes
server:
private-domain: "plex.direct"