@RichMT What would probably be a better setup is to configure all C9 units except the one wired to the modem as a access point. When you log into the router go to Advanced > Operation Mode (left side). You will be able to select Access Point Mode there.

It would be best to have them all wired to a switch, and then a Ethernet cable from a switch to the C9 acting like the router.

However, if you are not able to do that you can set up each router with the current wiring setup. 

What would probably be easiest is to go to the first C9 that is to be a access point, write down its MAC address on the bottom sticker label. Next thing is to disconnect the WAN port and LAN port, now connect to the router Either via Wi-Fi or using a Ethernet cable on your computer. Finalize any wireless settings you wanted as for as wireless name and password in the menu Advanced > Wireless > Wireless Settings. Now configure the Access Point mode. Once you select save and while the router is rebooting connect the WAN and LAN back, you can move on to the next router. 

If for some reason you have a issue with the congurations you can reset the router by holding the WPS/Reset button for 15 seconds. The router will do a complete factory reset and go back to router mode, and the Wi-Fi that will be broadcasted will be what is printed on the label of that device.

Once all the routers are now in access point mode, you can then log into the main router, and look at the connected clients. Based off of the MAC address youw ill know which router has what IP so you can log into it and modify any wireless settings in the future if you would like.

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