A Network Administrator Needs to Allocate a New Network for the R&D

A network administrator needs to allocate a new network for the R&D group. The network must not be accessible from the Internet regardless of the network firewall or other external misconfigurations. Which of the following settings should the network administrator implement to accomplish this?

A) Configure the OS default TTL to 1
B) Use NAT on the R&D network
C) Implement a router ACL
D) Enable protected ports on the switch