An engineer has configured a VXLAN tunnel between remote data centers, but the VXLAN tunnel is not established. Which reason for this tunnel failure is most likely true?
A. The transport network does not support Bidirectional PIM.
B. Multiprotocol BGP is missing a route reflector.
C. Multipoint GRE tunnels are not configured between data centers.
D. An ACL exists on the physical network between the data centers that block UDP port 4789.
