The Domain Name System (DNS) matches the domain names you type into a web browser with a numeric IP address which represents their location on the internet and which the browser uses to return the site’s data. DNS filtering refers to a technique that is used to block malicious websites in order to filter our inappropriate or malicious content. This ensures that data remains secured and also allows companies to control what sites their employees can access on company owned networks.

Filtering in the DNS operates through the use of a blocklist. This list contains all the known domain names and addresses of harmful sites; when a domain is sent to the DNS and it appears on the blocklist it is not resolved and cannot be accessed. Blocklists are maintained by users in the internet community so that when a malicious site is identified it is added automatically so that other users are not harmed.