Multicast DNS (Domain Name System)resolves host names to IP addresses within small networks that do not include a local name server. It is a zero-configuration service, using essentially the same programming interfaces, packet formats and operating procedures as the unicast Domain Name System (DNS). It is designed mDNS to be stand-alone capable, but it can work in concert with unicast DNS servers.
The mDNS protocol is published as RFC 6762, uses IP multicast User Datagram Protocol (UDP) packets.
mDNS can work in conjunction with DNS Service Discovery (DNS-SD), a companion zero-configuration technique specified separately in RFC 6763.
It is used by Apple Bonjour and several of the audio and video over IP systems for discovery.
See DNS, DNS-SD