Negative answers

[richardschneider]

A Multicast DNS responder MUST only respond when it has a positive,
non-null response to send, or it authoritatively knows that a
particular record does not exist. For unique records, where the host
has already established sole ownership of the name, it MUST return
negative answers to queries for records that it knows not to exist.
For example, a host with no IPv6 address, that has claimed sole
ownership of the name "host.local." for all rrtypes, MUST respond to
AAAA queries for "host.local." by sending a negative answer
indicating that no AAAA records exist for that name. See Section
6.1, "Negative Responses". For shared records, which are owned by no
single host, the nonexistence of a given record is ascertained by the
failure of any machine to respond to the Multicast DNS query, not by
any explicit negative response. For shared records, NXDOMAIN and
other error responses MUST NOT be sent.