I have run a Minecraft server for over a year. I had a netgear router on Comcast network. We recently got a 'new' all-in modem/router, one that needed to be configured. http://canyouseeme.com says that the external port is being forwarded at 25565, but I can only access the server on my internal network. This is really bugging me, and I am out of ideas. Here are the pictures I have of my trials.
Note: I assigned my server computer a static IP of 10.0.0.28 so there is no problem with the internal IP of the server computer not matching the IP address that is in the port forward settings.
In response to a below comment: I used to connect to my server using the external address even though I was on the local network. My computer is on same network as my server. I can log on with my direct connection but not with the external IP. This leads me to think that there is a problem.