Explanation
The administrator should perform an antivirus scan on all servers within the cluster and reboot each server, and block access to 208.206.12.9 from all servers on the network. These actions will help to remove any malware that may have infected the application server and prevent any further unauthorized traffic to the known-bad public IP address. An antivirus scan can detect and remove malicious software that may be sending data to an external source, and a reboot can clear any temporary files or processes that may be related to the malware. Blocking access to 208.206.12.9 from all servers on the network can prevent any future attempts to communicate with the malicious IP address.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 3, Lesson 3.4, Objective 3.4; Chapter 6, Lesson 6.2, Objective 6.2