Gotcha. It’s possible your modem was trying to act as a router as well, which would cause a Double-NAT situation. Most ISPs will ship a modem/router combo, but the router part is always fucking dog water. And the issue with double-router setups is that if you try port forwarding on your router, the ISP’s router won’t automatically detect the open port, so you’ll still be blocked.
If you do end up looking into it again, see if the modem allows you to set up bridge mode or DMZ mode, and point it to your router. (You’ll need to undo any old port forwarding stuff you attempted last time first, or else it won’t work!) Basically, this takes all of the modem traffic and passes it directly to your router, instead of trying to do routing on the modem/router. Which is honestly what you want, because your personal router is almost certainly going to be better than the shitty one they ship. This will eliminate the Double-NAT situation, because the ISP’s router is going to be completely disabled and is passing all of the traffic directly to your router.
It’s also possible that CenturyLink runs CG-NAT, which would cause a Double-NAT situation on the ISP’s side. More and more ISPs are running CG-NAT to avoid transitioning to IPv6 as long as possible. Basically, there aren’t enough IPv4 addresses available anymore, so ISPs have started giving the same IPv4 address to multiple users using CG-NAT. Your public IP will be shared with multiple users via CG-NAT, the same way your router is sharing the internet connection with multiple devices via NAT. You can check your public IP address in your modem (or your router, if you set up DMZ earlier.) If you’re within the 100.64.x.x to 100.127.x.x range, CenturyLink probably has you on CG-NAT (since those are the public addresses reserved for CG-NAT.) But this breaks port forwarding, because you would also need to forward the port at the carrier level, (which you have no way of doing.)
If they do have you behind CG-NAT, your only real option is going to be a reverse proxy. Basically, Plex/Jellyfin would ping a remote server, which then proxies the request down to your server. It wouldn’t require any port forwarding on the server’s side, because the proxy will be using https directly. Nginx is a popular free reverse proxy service.
Gotcha. It’s possible your modem was trying to act as a router as well, which would cause a Double-NAT situation. Most ISPs will ship a modem/router combo, but the router part is always fucking dog water. And the issue with double-router setups is that if you try port forwarding on your router, the ISP’s router won’t automatically detect the open port, so you’ll still be blocked.
If you do end up looking into it again, see if the modem allows you to set up bridge mode or DMZ mode, and point it to your router. (You’ll need to undo any old port forwarding stuff you attempted last time first, or else it won’t work!) Basically, this takes all of the modem traffic and passes it directly to your router, instead of trying to do routing on the modem/router. Which is honestly what you want, because your personal router is almost certainly going to be better than the shitty one they ship. This will eliminate the Double-NAT situation, because the ISP’s router is going to be completely disabled and is passing all of the traffic directly to your router.
It’s also possible that CenturyLink runs CG-NAT, which would cause a Double-NAT situation on the ISP’s side. More and more ISPs are running CG-NAT to avoid transitioning to IPv6 as long as possible. Basically, there aren’t enough IPv4 addresses available anymore, so ISPs have started giving the same IPv4 address to multiple users using CG-NAT. Your public IP will be shared with multiple users via CG-NAT, the same way your router is sharing the internet connection with multiple devices via NAT. You can check your public IP address in your modem (or your router, if you set up DMZ earlier.) If you’re within the 100.64.x.x to 100.127.x.x range, CenturyLink probably has you on CG-NAT (since those are the public addresses reserved for CG-NAT.) But this breaks port forwarding, because you would also need to forward the port at the carrier level, (which you have no way of doing.)
If they do have you behind CG-NAT, your only real option is going to be a reverse proxy. Basically, Plex/Jellyfin would ping a remote server, which then proxies the request down to your server. It wouldn’t require any port forwarding on the server’s side, because the proxy will be using https directly. Nginx is a popular free reverse proxy service.