DNS Response Policy Zones (RPZ)
V. Schryver, Paul Vixie · 2016
This document describes a method for expressing response policy inside a specially constructed zone, and for recursive name servers to use such policy to return modified results to clients. The modified results can stop access to selected HTTP servers, redirect users to walled gardens, block objectionable email, and otherwise defend against attack. These DNS Firewalls are widely used in fighting Internet crime and abuse.