moodns

moodns is a server implementation of multicast DNS. Multicast DNS allows programs to discover hosts running on a local network by using familiar DNS programming interfaces without the need for a conventional DNS server.

Features

No configuration required.
Support for forwarding unicast DNS queries to multicast servers which can be used for transparently enabling client-side multicast DNS with minimal config changes (see caveats below).
No dependencies (e.g. dbus) required.

Getting Started

There's not much to it, just run:

$ sudo moodns

moodns will start answering multicast DNS queries for the local host (i.e. those asking for the $HOST.local domain name, unless an alternative hostname is provided).

In order to enable multicast DNS on a client computer one can either install nss-mdns (recommended), or enable the forwarding of unicast requests in moodns.

"Multicast forwarding" allows moodns to receive DNS queries via unicast (like any traditional DNS server) and automatically forward those queries to other hosts via multicast DNS (essentially, moodns will receive the unicast query, forward it to the multicast DNS address, receive the multicast response and forward that response back to the client via unicast).

This mode can be enabled by running moodns with the --enable-multicast-forward option and then configuring the client computer to use moodns as DNS server.

Start moodns like this:

$ sudo moodns --listen ':5353,:53' --enable-multicast-forward

Then edit the /etc/resolv.conf file and add nameserver 127.0.0.1 to the top of the file. Note that the --listen ':5353,:53' option is needed because some system DNS resolvers (e.g. glibc's) do not support setting the name server port and always use 53. If your system resolver supports changing the port (e.g. Mac OS X, Solaris, OpenBSD) you don't need that option (nor running moodns as root).

moodns will only answer queries for *.local domain names, and if it receives a query for another domain name it will return an error so that the querier will fallback to another DNS server without waiting for the timeout to expire (remember to configure /etc/resolv.conf with multiple nameserver lines).

Note however that this mode is not recommended. It's not part of the multicast DNS specs and is really just a hack which may break your system in unexpected ways. Unless you know what you are doing, use nss-mdns instead.

See the man page for more information.

Building

moodns is distributed as source code. Build with:

$ go get github.com/ghedo/moodns/cmd/moodns
$ go get github.com/ghedo/moodns/cmd/moodns-resolve

ToDo

Reverse multicast DNS lookup
Full IPv6 support
DNS-based service discovery (RFC6763)
Name compression in DNS queries and answers
Startup probing and announcing support
Conflict resolution support
Known-answer suppression (incl. multipacket) support

Copyright

See COPYING for the license.

ghedo / moodns