Plex uses TCP. The rule for UDP is not needed.
To check remote access status, your Plex Media Server checks in on a regular basis with a plex.tv host. Sometimes the check-in fails (time-out, net congestion, etc) but remote access still works. When this happens your server will show remote access as not working when it is really still available. Plex made some changes to Plex Media Server and their backend hosts last year (May/June) to improve the process, but the situation can still occur.
You can check if remote access is working outside of the Plex Remote Access status page:
canyouseeme.org
From a system on the same network as your server, go to canyouseeme.org.
Replace the default port with your Plex remote access port & click Check Port.
Success means it can reach your server.
Uptime Robot
Uptime Robot will check remote access every five minutes and send an e-mail if it cannot reach your server. The web interface also has a nice dashboard showing percent uptime, listing when connectivity was lost & regained, etc. The basic free account works fine for monitoring a Plex server. Your Plex server must be using manual port forwarding. With automatic, your remote access port will change when you restart your server, etc, which would break monitoring by Uptime Robot.
