Does port forwarding work from inside the network?

Question

Say you have a router with external ip 42.1.98.9, with the port 10443 set to forward all incoming TCP/UDP packets to host 192.168.1.200. The routers internal network address is 192.168.1.100.

say there are two NICs connected to the router, with internal IP 192.168.1.200 and 192.168.1.300.

I've noticed that packets sent to socket 42.1.98.9:10443 gets redirected to 192.168.1.200, which is the expected behaviour.

However, say the computer 192.168.1.300 sends a packet to socket 192.168.100:10443. In other words a computer from inside the network is sending a packet to the router, in a port that should theoretically redirect incoming packets.

On that scenario, I'm not noticing the packets being redirected to the proper host -- 192.168.1.200.

Why is that? Does port forward on the router occur only for packets being sent to its external IP address?

Thanks

Answer 1

Yes, generally port forwarding is only from the external address to internal addresses. I'm guessing a commercial-grade router could be programmed to do what you want, but not any home router I've ever seen.

You should be able to use the router's external address from inside the network though (i.e., send packets from 192.168.1.300 to 42.1.98.9:10443 and it should redirect to 192.168.1.200:10443).