Installing and enabling rdnssd by default

Leon Weber leon at
Thu Sep 8 14:30:36 UTC 2011

Hi all,

in the process of implementing IPv6 in my home network, I noticed that
one of the major points preventing the IPv6 implementation from
reaching IPv4-quality is the lack of support for DNS autoconfiguration.
I also help building networks for hacker events from time to time,
where the idea of offering IPv6-only connectivity regularly comes up
and usually has to be discarded for mostly this reason. It is also one
of the main conclusions that Arkko & Keranen of Ericsson draw from their
extensive testing in an IPv6-only network (see [0]).

While there are two methods available to implement DNS autoconfiguration,
namely DHCPv6 and including the RDNSS information in Router Advertisements
as specified in RFC 6106[1], I prefer the latter solution, as it is simpler
and more elegant while providing all the functionality most environments
need. (However, I am convinced that this particular question is a matter
of personal taste and will be subject of neverending debates in the
future, so eventually, both methods will need to be implemented.)

The RFC 6106 method is implemented by radvd on the server side and
a userland daemon named rdnssd on the client side. This daemon reads the
recursive DNS server information from Router Advertisements and updates
/etc/resolv.conf accordingly. rdnssd[2] is included in Ubuntu, however
it is not installed and enabled in the default installation. I suggest
to change this.

Possible downsides include:
* One more process that is running all the time on everyone's
* Possible security issues (since more code running generally means more
  places for bugs to hide).

Since rdnssd's resource usage are negligable and it really is not a lot
of code, I believe those are no serious problems. Instead, I think the
fact that Neighbour Discovery is enabled by default actually demands to
also enable rdnssd in order to provide a complete autoconfiguration
process that does not rely on IPv4 connectivity.

In conclusion, I think this is a relatively minor change that would
complete the Stateless Address Autoconfiguration process and remove a
majorblocker for IPv6-only networks. Such networks might be rare today,
but there is no doubt they will be common in the future.


    -- Leon.


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