[atlas] Strong doubts about the option "DNS recursion"

On Fri, Oct 25, 2013 at 12:15:28PM +0200,
 Stephane Bortzmeyer <bortzmeyer at nic.fr> wrote 
 a message of 35 lines which said:

> {'definitions': [{'query_class': 'IN', 'use_probe_resolver': True, 'af': 4, 'query_argument': 'd7b16b2a97627e8ccbcccf93e773ec3f.cosmogol.fr', 'query_type': 'TXT', 'type': 'dns', 'is_oneoff': True, 'recursion_desired': False, 'description': 'DNS resolution of d7b16b2a97627e8ccbcccf93e773ec3f.cosmogol.fr'}], 'probes': [{'requested': 10, 'type': 'area', 'value': 'WW'}]}

I created a second domain by the same method, changed only the
recursion_desired option and got exactly the same result (measurement
#1034374):

{'definitions': [{'query_class': 'IN', 'use_probe_resolver': True, 'af': 4, 'query_argument': 'ea4f6f5b9176b3d55061e5bd85410c1b.cosmogol.fr', 'query_type': 'TXT', 'type': 'dns', 'is_oneoff': True, 'recursion_desired': True, 'description': 'DNS resolution of ea4f6f5b9176b3d55061e5bd85410c1b.cosmogol.fr'}], 'probes': [{'requested': 10, 'type': 'area', 'value': 'WW'}]}

So, it seems as if recursion_desired is ignored and the reality is that
the RD bit is always set.

By the way, this investigation was done because some people, to
monitor the content of the DNS caches, use open resolvers
(<https://indico.dns-oarc.net//getFile.py/access?contribId=7&resId=1&materialId=slides&confId=1>
and <http://samarudge.github.io/dnsyo/>) and I tought it would be
better to use Atlas probes. But the tests may have to be run without
RD, otherwise you risk "poisoning" the caches, if you use the
measurement to test a hijacking, for instance, as in the first example
mentioned.