@Ncg206,

Your Deco XE5300 should be simply treated as another router. You can only have one router on your network, which should be wired directly to the modem.

First off, I recommend taking a look at this FAQ on the differences between using a Deco in AP Mode vs Router Mode: What is the Difference Between Router and Access Point(AP) Mode?

If you are looking to use all the network management and routing features of your Deco, you will want to replace your C4000 with the Deco, as there can only be one router active on the network at a time. If needed, you could then set the C4000 up in Access Point Mode, which will extend your wireless network when given a wired connection; however this may not even be needed since you are moving to a mesh-based network.

If you would like to keep your C4000 at the head of your network, you will need to configure your Decos in AP Mode. This will disable some of the features and will simply forward the traffic through the C4000.

In general, it is recommended to use the Deco's in Router Mode and connect them directly to your modem, as this will simplify and optimize your connections. If you need the additional ethernet ports, you may always place a network switch AFTER your Deco, or even after one of your satellite Deco's ethernet ports.