An administrator needs to connect a router in one building to a router in another using Ethernet. Each router is connected to a managed switch and the switches are connected to each other via a fiber line. Which of the following should be configured to prevent unauthorized devices from connecting to the network?
A. Configure each port on the switches to use the same VLAN other than the default one
B. Enable VTP on both switches and set to the same domain
C. Configure only one of the routers to run DHCP services
D. Implement port security on the switches