The Cisco Umbrella Domain Blocked rule is designed to monitor and identify instances where domains are blocked by the Cisco Umbrella DNS service. This detection rule helps maintain security by flagging attempts to access potentially malicious sites. When a domain is blocked, it logs details including the internal and external IP addresses, the domain name, the action taken (Blocked), and the response code. The rule operates on a deduplication period of 480 minutes, ensuring that repeated alerts for the same blocked domain are minimized. The rule is activated when a blocked response is logged, delineating the network activity for blocked domains with low severity. Security operators should inspect the blocked domains to ascertain whether they correspond to known threats or malware. In case of a blocked domain, the expected result from the tests confirms that the domain access was appropriately denied. The rule includes a reference link to Cisco's support documentation for further clarification.