Which statement about dynamic GRE between a headend router and a remote router is true?

In dynamic GRE, the headend router learns the IP addresses of remote routers dynamically through a mechanism like NHRP (Next Hop Resolution Protocol), rather than relying on static configuration.

A GRE tunnel interface configured without an IP address might be up, but it would not be functional for routing IP traffic; 'administratively down' specifically means the interface has been manually disabled.

While it is true that GRE tunnels *can* be established with dynamic remote IP addresses in dynamic GRE (e.g., DMVPN), this capability is achieved precisely because the remote router initiates the connection and registers its dynamic IP, making option D a more fundamental aspect of the dynamic process.

In dynamic GRE deployments such as DMVPN, the remote (spoke) router is explicitly responsible for initiating the tunnel connection to the headend (hub) router. This initiation is critical because the headend router often does not know the dynamic or changing IP address of the remote router beforehand and thus cannot initiate the connection itself.