[dns-operations] resolvers considered harmful

Mark Allman mallman at icir.org
Thu Oct 23 01:07:08 UTC 2014

Let me try to take care of both of these related points together:

Joe Greco <jgreco at ns.sol.net>:
> Then we merely move on to the issue of cache poisoning individual
> clients.
> Assuming that the CPE is a NAT (effectively firewalling clients from
> poisoning attacks) and/or that the individual clients have well-
> designed, impervious resolvers is likely to be a fail.

David Conrad <drc at virtualized.org>:
> As I understand it, you're proposing pushing the resolvers out to the
> edges 

That is not what we are proposing.  We are not suggesting resolvers be
*moved*, but rather *removed*.  That is, clients simply do name lookup
on their own.

Name lookup at an endpoint is different from name lookup in an
intermediate resolver.  

An intermediate resolver looks up a name on behalf of other hosts.  It
therefore *must* listen for lookup requests that roll in from the
network.  This is fundamental to a resolver's operation---it simply
*must* accept requests from other hosts.  Don't get me wrong.... it
doesn't have to accept all requests and as we know, too many resolvers
accept requests they should not.  All I am saying is that the resolver
cannot do its job without accepting requests from other hosts.

On the other hand, an endpoint can look up a name without listening for
any request from the network.  We suggest this be an entirely local
operation.  Think of it like this: just because I want to load the
cnn.com web page I don't have to run httpd.  Well, just because I want
to look up an A record for cnn.com doesn't mean I have to run bind.

Could there be attacks against the internal lookup process on a host?
Of course.  But, those are attacks that require some sort of access to
the end host first.

David Conrad <drc at virtualized.org>:
> if you're not doing DNSSEC at the edges,

Let me be clear.... I am not arguing against DNSSEC.  A crypto signed
record is always better than a clear text record.  But, DNSSEC is still
not here and it seems to me that factoring out some of the
intermediaries that we know sometimes both play games and have games
played on them may well be a useful path.


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