[SOLVED] Difficulty With Minecraft Server

This is yet another "cant set up a Minecraft server" post ... I'm hoping someone can help. The server works on my computer but it is not working on his.

Our computers are connected by Ethernet cable directly to the ASUS RT–AC86U router. His local IP address in the US is 192.168.50.166.

These are the settings for port forwarding:

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

When he runs Minecraft on his own computer and direct connects to 192.168.50.166, he connects. If he enters an external IP (obtained through the "Network Map" page of the router settings), it returns the error:

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

When I attempt to connect from my computer to 192.168.50.166, I get the exact error from Minecraft.

Here's the real kicker: Everything works when I run the server on my personal computer (192.168.50.48) and modify the Local IP port forward settings accordingly.  Minecraft Survival Games Servers  can connect to the Minecraft server with either my local IP, or an external IP.