How to configure different IP classes on the WAN and LAN

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Braavos wrote:

Thanks CrimpOn , for your prompt reply, so in short if  I have one public IP from the ISP I cannot use it on the router and still create a DHCP on the Orbi LAN?

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It is probably useful to confirm how many "routers" we are talking about.

ISP's provide one public IP address to a customer.  That is the WAN (internet) IP address on the router.  The router in turn creates a private IP network on the LAN side.  One router: one LAN network.

A second router (perhaps an Orbi) can be connected to one of the LAN ports on the primary router.  The WAN IP address on that second router will get an IP address from the primary router.  It will then create its own LAN side network, with a different IP address space.  All of the devices connected to that second router will have different IP addresses than everything connected to the primary router.  This is commonly described as a "Double NAT" situation: https://kb.netgear.com/30186/What-is-Double-NAT 

I have stacked as many as three routers.  Devices on the third router can access the internet, but there are major complications getting them to access devices connected to the first two routers and things such as internet gaming, opening ports, VPN, etc.

So, each router has one WAN IP and creates one LAN network.