So I'm setting up a file server for a summer camp. Simple setup. Server box is in the main office at the top of the hill, behind a static public IP address (XXX.XXX.124.164). Works fine with internal connections and most external ones around town. Firewall is autoblocking login attempts from Malaysia. Good times.
Now, I head down to the hill to the main lodge. The devices are behind a DIR-859 router and a different cable modem than the office. Its public dynamic IP address is from the same ISP and block of IP addresses (XXX.XXX.124.166).
Now:
Connecting via any other location/connection CAN ping the XXX.XXX.124.164 IP address and connect to my remote file server.
Plugging my laptop directly into the cable modem CAN ping the XXX.XXX.124.164 IP address and connect to my remote file server.
Plugging my laptop into the DIR-859 router which is plugged into the cable modem CANNOT ping the XXX.XXX.124.164 IP address or connect to my file server but CAN ping and connect to other sftp servers across the web.
So the problem appears to be specific to the router, and specific to IP addresses which are nearby. What settings or further debug information should I be looking at to fix this?