Port Forwarding puzzle

I have a puzzle that I need help with.

We have two PLCs, each with a built-in webserver. They have been assigned IPs of 192.168.1.5 and 192.168.1.8. They talk to each other via Ethernet and are connected through a switch. The switch is also connected to a consumer-grade Asus router which connects to a cable modem. We have paid extra for a static IP.

If I connect a laptop to the router I can access either PLC by entering the IP in my browser. If I set up Port Forwarding to allow access to 192.168.1.5 from the internet I can connect to the PLC from outside the network just fine. But if I change the Port Forwarding settings to access 192.168.1.8 I get a “Server not responding” error.

I can’t understand why one works and the other doesn’t. Especially since they both work fine through the router.

Any thoughts?

Solution 1:

Seem like to me you forgot to add a default gateway in that PLC.