Authenticated Denial of Existence in the DNS
RFC 7129

Received changes through RFC Editor sync (changed abstract to 'Authenticated denial of existence allows a resolver to validate that a certain domain name does not exist. It is also used to signal that a domain name exists but does not have the specific resource record (RR) type you were asking for. When returning a negative DNS Security Extensions (DNSSEC) response, a name server usually includes up to two NSEC records. With NSEC version 3 (NSEC3), this amount is three.

This document provides additional background commentary and some context for the NSEC and NSEC3 mechanisms used by DNSSEC to provide authenticated denial-of-existence responses.')