I have read through the forums, googled, followed the FAQs, and nothing I try seems to work, so I thought I would try the community.
Problem: I can connect to and play my content from within my network, but my server is unreachable remotely. I get the green arrow pointing from Public to Local on the Plex preferences, but the red "x" between Internet and Public.
My setup: Cable internet coming into an Arris TG2472 modem. That modem is directly wired into a MacMini, which runs the Plex server. The modem is also hard-wired into an iMac and an Eeros wireless router, but that is unlikely to be relevant, since the Mini has a hard-wired connection of its own, and the problems remain when wireless is turned off on the mini. The mini connects to the internet fine in other apps (e.g., Safari).
What I tried: I turned off the modem's firewall. I clicked Plex's "manually specify public port" (32400). I toggled UPnP on the modem. I then set the modem to manually assign an IP address to my Mini (192.168.0.110), and port-forwarded (using 32400 as both the WAN and LAN ports). I tried putting the Mini in a DMZ. And of course I tried restarting the server/Mini/Modem, and logging out and back in to Plex on the server.
I am officially at a loss. The only clue I have is that using the open port check tool at canyouseeme.org does not show 32400 as open (it gets a "connection refused"). That said, the way to forward the port on my modem is simple and straightforward (I double-checked and used the directions at port forward.com), so I find it tough to believe that part isn't working.
Would love help - this worked fine when I had a different modem, but when I upgraded service with Cox they said my faster service needed to use this modem!