Unless you've changed the default settings, the ASUS is setup as a home router and is providing IP addresses to devices connected to it's LAN by Ethernet or WiFi. You need to disable it's DHCP server and assign it's GUI a static IP on the G1100.
Before you start this process, make sure you know how to factory reset the Asus using a button or external control. If something doesn't go right, you may not be able to connect to the Asus until you factory reset it.
To do this, disconnect the Asus from the G1100. Connect a computer to the Asus's LAN via Ethernet or WiFi. You should then be able to access it's GUI on whatever it's default IP address is (consult the Asus docs, if needed). Then, figure out how to turn off it's DHCP server. Next, find where the router's own IP address is configured and change that to an available IP address on the G1100's LAN.
Turn off the Asus. Connect an Ethernet cable between the G1100 and Asus. Power the Asus back up. It's GUI should now be available on the IP address you configured above. You should now create a static IP entry in the G110 to make sure the IP address isn't assigned to any other device.
There are many ways to solve this problem. Here's another approach: