@Denizn 

What router function do you expect the Deco to do if the WAN port is in the same subnet as the LAN ports and the wifi network?

Why do you not want to run the Deco in AP mode?

  @yves_b VPN for example. Could you let me know what is required for this feature to be added?

  @Denizn you do NOT need to turn off NAT and DHCP for VPN. In fact, your devices actually need them both on to get online and connect to the VPN. 
 

You can't connect to a VPN with them off. 

  @Richardj186 But my modem is handling these already, I would like to turn off DHCP on the router so that there isn't a duplication. Is this possible to add?

  @Denizn no you can NOT turn them off when your Deco's are in router mode, they're an essential part of every router. Your primary Deco (the one connected to the modem) uses DHCP and NAT to give IP addresses to your other Decos and your devices online. 
 

Modems don't have DHCP or NAT capability, that's why you need them turn ON with routers. Otherwise, none of your devices will go online. 
 

And no, I can't find any other posts asking about removing DHCP or NAT when in any mode. 

  @Richardj186 I know I can't do this right now. This is why it is a feature request. Can it be added?

Denizn wrote

  @Richardj186 I know I can't do this right now. This is why it is a feature request. Can it be added?

  @Denizn no, because then your router would not work. You need DHCP and NAT to get online. 
 

DHCP gives all your devices (and other Decos) IP addresses on your network. NAT is what allows those devices to get online and visit websites, watch videos, download files and updates, etc.  

You won't be able to get online if you disable either or both of them on your Decos (or any other router) when they're in router mode. Period.