DNS-based blocking is a filtering method that intercepts domain-name lookups and refuses, redirects, or null-routes requests for known ad, tracker, or malware domains. Because many apps must resolve a hostname before they can connect, blocking at the DNS layer can stop unwanted traffic before a connection is established.
In cyber security, this technique is useful for reducing exposure to malicious infrastructure, suppressing telemetry, and cutting off some phishing or command-and-control domains. It is common in security tools, home filters, and enterprise resolvers. However, it is not a full defense: attackers can use hardcoded IP addresses, fast-changing domains, DNS-over-HTTPS, or compromised legitimate sites to bypass simple filters. DNS-based blocking works best as one layer in a broader defense that also includes endpoint protection, browser hardening, and user awareness.