[SOLVED] Difficulty With Minecraft Server

This is yet another "cant' set up a Minecraft server" post ... I hope someone can assist me. The short version is that the server works on my computer, but not on his.

Our computers are connected by ethernet cable directly to the ASUS RT–AC86U router. The IP address of his local computer is 192.168.50.166.

The port forwarding settings are:

Service Name: Minecraft Source IP (blank). Port Range: 2565 Local IP: 192.168.50.166 Port: 25565 TCP : BOTH

If he is running Minecraft on his own computer and direct connects to 192.168.50.166, he connects. If you enter an external IP (obtained through the "Network Map" page in the router settings) it will give the error message:

Failed to connect to the server io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection timed out: no further information

I am getting the same error in Minecraft when I try to connect to 192.168.50.166 from my personal computer.

But here's the real kicker ... If  Minecraft online  run the server on MY computer (192.168.50.48) and change the Local IP port forward settings according to my preferences, everything works. I can connect to the Minecraft server using either my local IP, or the external IP.