CGA4131COM Version 2.1 Port Forwarding is not working

I have CGA4131COM version 2.1 for Comcast Business.

I went into admin and port forwarded 5000 - 5010 to one of my device which is attached to CGA4131COM by ethernet.

Now I can access the device from outside by mypublicip:5000 using various ISPs.

However from other devices which are attached to the CGA4131COM inside my house, I cannot reach the device by mypublicip:5000. I can only use the localip:5000 to reach the device.

Why is that and how can I fix this?