Context:

Main router network 192.168.1.1/24

2nd router with its own network 192.168.2.1/24

Main router has assigned 192.168.1.100 to the WAN port of the 2nd router.

A system on the 2nd network at 192.168.2.5 needs a few ports forwarded to it from the WAN port (which is connected to the main LAN at 192.168.1.100, and not the public internet).

Issue:

I want to access the web interface of the 2nd network from the main network at its WAN address of 192.168.1.100:80 BUT port 80 is already being forwarded to another system at 192.168.2.5 so the routers web interface port for the WAN cannot be accessed at 192.168.1.100 since it is being told to forward everything going to port 80 on the WAN 192.168.1.100 to port 80 at 192.168.2.5

Solution:

set up a port forward using another port like 8080 on 192.168.1.100 to 192.168.2.1

Now when on the main network 192.168.1.1/24 the 2nd network web interface can be reached by going to 192.168.1.100:8080