DMVPN dual hub single cloud
A DMVPN dual hub single cloud topology delivers a single DMVPN network with a second hub. The spoke routers will use only one multipoint GRE interface, and the second hub is configured as a next-hop server.
Such a topology does deliver redundancy at the hub, and it is very easy to configure, however, it can introduce some problems with routing. Dynamic routing protocols will see the two hubs as equal-cost paths, resulting in equal-cost load balancing. Although this is desirable in some situations, it may not be when applied to DMVPN.
It can be difficult to configure a routing protocol, such as OSPF for example, to prefer one hub over the other. Because of this, it is best practice to avoid using a dual hub single cloud DMVPN topology, and prefer a DMVPN dual hub dual cloud option instead.