An access control list (ACL) is a set of rules that defines which traffic is allowed or denied on a network device, such as a router or a firewall12.
An ACL can be used to filter traffic based on various criteria, such as source or destination IP address, port number, protocol, or time of day12.
By implementing an ACL on the edge router of the network, the network administrator can block the unauthorized IP address from entering the secure part of the network every night at 8:00 pm12.
This solution would address the concerns of the network administrator, as it would prevent the unauthorized IP address from accessing the critical server or any other resource on the secure network12.
Changing the VLAN of the web server (A) or changing the server's IP address (B) would not stop the unauthorized IP address from entering the network, as it could still scan the network for other open ports or vulnerabilities12.
Instating a rule on the firewall connected to the web server (D) would only protect the web server, but not the rest of the secure network, from the unauthorized IP address12. Reference:
CompTIA Network+ N10-008 Certification Study Guide, Chapter 4: Network Operations, Section 4.3: Network Security Devices and Technologies, pp. 212-213.
Professor Messer's CompTIA N10-008 Network+ Course, Section 4.3: Network Security Devices and Technologies, Video: Access Control Lists.