The Domain Name System (DNS) matches the name of website domains that you type into your browser with a numerical IP address that represents the server on which they are located. DNS filtering refers to the process of filtering malicious websites so that harmful content can be blocked.
Specially configured software in the DNS acts as a filter by refusing to translate (or resolve) the name of specific domains that are maintained in a ‘block list’ thus preventing users from reaching those domains. DNS can filter websites either by their domain names or IP addresses. Block lists are a list of known harmful sites that is maintained by the overall cyber community as well as those that have been identified by DNS filtering vendors. Some DNS filtering software is able to evaluate websites and add them to the block list automatically based on certain of their characteristics.