An engineer is attempting to establish a new site-to-site VPN connection. The tunnel terminates on
an ASA 5506-X which is behind an ASA 5515-X. The engineer notices that the tunnel is not
establishing. Which option is a potential cause?

A.
Certificates were not configured

B.
Diffie – Helman Group is not set

C.
Access lists were not applied

D.
NAT – traversal is not configured