A Cisco ASA is operating in transparent firewall mode, but the MAC address table of the Cisco ASA is always empty, which causes connectivity issues. What
should you verify to troubleshoot this issue?

A.
if ARP inspection has been disabled

B.
if MAC learning has been disabled

C.
if NAT has been disabled

D.
if ARP traffic is explicitly allowed using EtherType ACL

E.
if BPDU traffic is explicitly allowed using EtherType ACL

Explanation:
http://www.cisco.com/en/US/docs/security/asa/asa82/configuration/guide/fwmode.html#wp1224