A company's security policy requires that all connections between sites be encrypted in a manner that does not require maintenance of permanent tunnels. The sit...

A company's security policy requires that all connections between sites be encrypted in a manner that does not require maintenance of permanent tunnels. The sites are connected through a private MPLS-based service that uses a dynamically changing key and spoke-to-spoke communication. Which type of transport encryption must be used in this environment?

A. GETVPN B. DMVPN C. GRE VPN D. standard IPsec VPN