When designing the Network Admission Control （NAC） Appliance for the Enterprise Campus Network， which of the following requirements would help the designer to narrow down the NAC choices， from Virtual Gateway to Real IP Gateway， or from In-band to Out-band？（）

A. QoS ToS/DSCP values are required to be forwarded transparently
B. Device redundancy is required
C. Per-user ACL support is required
D. Multicast service support is required