The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network.
mDNSResponder — Multicast DNS daemon
mDNSResponder (also known as mdnsd on some systems) is a daemon invoked
at boot time to implement Multicast DNS and DNS Service Discovery.
mDNSResponder listens UDP port 5353 for Multicast DNS Query packets.
When it receives a query for which it knows an answer, mDNSResponder
issues the appropriate Multicast DNS Reply packet.
mDNSResponder also performs Multicast DNS Queries on behalf of client
processes, and maintains a cache of the replies.
mDNSResponder has no user-specifiable command-line argument, and users
should not run mDNSResponder manually.
To examine mDNSResponder’s internal state, for debugging and disagnostic
purposes, send it a SIGINFO signal, and it will then dump a snapshot sum-
mary of its internal state to /var/log/system.log, e.g.
sudo killall -INFO mDNSResponder
For information on Multicast DNS, see http://www.multicastdns.org/
For information on DNS Service Discovery, see http://www.dns-sd.org/
For information on how to use the Multicast DNS and the DNS Service Dis-
covery APIs on Mac OS X and other platforms, see
For the source code to mDNSResponder, see
mDNSResponder bugs are tracked in Apple Radar component „mDNSResponder”.
The mDNSResponder daemon first appeared in Mac OS X 10.2 (Jaguar).
Also available from the Darwin open source repository (though not offi-
cially supported by Apple) are mDNSResponder daemons for other platforms,
including Mac OS 9, Microsoft Windows, Linux, FreeBSD, NetBSD, Solaris,
and other POSIX systems.