A network engineer wants to connect two sites via a WAN technology and to securely pass multicast traffic over this WAN technology. Which WAN technology should be configured?

Pure IPsec does not support multicast traffic natively; it only encrypts unicast packets, making it insufficient for passing multicast across a WAN.

GRE alone supports multicast but provides no encryption or authentication, failing the security requirement.

Pure MPLS does not provide encryption and therefore does not meet the security requirement for securely passing traffic over the WAN.

GRE tunneling supports multicast and broadcast traffic natively, while IPsec alone only supports unicast. By combining GRE over IPsec, the multicast packets are first encapsulated in GRE (making them appear as unicast to IPsec) and then encrypted and authenticated by IPsec. This combination enables secure transmission of multicast traffic such as routing protocol updates across a WAN link.