radns is a free, small, portable client side implementation in C of the RDNSS option in IPv6 Router Advertisments (see RFC 5006) written by MC and released under a BSD license. FreeBSD is the development platform, but at least some versions have also been tested under Linux and MacOS X.
The program is meant to run on client machines in your IPv6 network. It is used to get the address to a resolving DNS server.
radns listens for Router Advertisements with the Recursive DNS Server (RDNSS) option and stores the addresses to the DNS servers in a file following the same syntax as resolv.conf(5). It optionally calls a script to handle, for instance, DHCP clients that compete for ownership of /etc/resolv.conf or to set the DNS server on systems that don't use resolv.conf at all.
Newest distribution first:
radns-0.9rc4.tar.gz 11kiB Feb 26, 2010.
radns-0.8.tar.gz 7.4kiB Sep 29, 2008.
radns-0.7.tar.gz 7.3kiB Sep 29, 2008.
radns-0.6.tar.gz 7.1kiB Aug 10, 2008.
radns-0.5.tar.gz 6.9kiB Jul 10, 2008.
There is a similar project, rdnssd, which is now part of the ndisc6 distribution.
I didn't know about rdnssd when I started my own project. However, having two similar projects that doesn't share any code and have different solutions to problems might help RFC 5006 to be accepted as a standard.