According to best practices, what is the proper placement of a firewall?

A. Only between the internal network and the Internet
B. At key security boundaries
C. In the DMZ
D. Only between the DMZ and the Internet

B. Firewalls should always be placed at key security boundaries, which can be the Internet and your internal network. However, proper placement is not exclusive to the boundaries of the Internet and internal networks. For example, it could be placed between two internal networks, such as R&D and guest networks.