Answer:
Defense-in-depth
Vendor diversity
Explanation:
The Defense-in-depth or the DiD means a security approach in information where a series of security mechanism and also controls are layered throughput the computer network in order to protect the confidentiality, availability and integrity of the network as well as the data within.
The security principle of Vendor diversity approach is a way of implementing the security controls from the different vendors to increase the security of the network.
Thus in the context, the supervisor is trying to promote the Defense-in-depth as well as the Vendor diversity principles of security by asking to install a Fortinet firewall between the Cisco firewall and its trusted LAN.