[atlas] DNS and recursion

Hi Stephane,

On 19/05/2017 14:35, Stephane Bortzmeyer wrote:
> API v1 had a field recursion_desired when performing DNS
> measurements. If I remember correctly (but I cannot find the reference
> right now), it worked only when querying a specific name server, and
> not when using the probe's own resolver, to avoid cache snooping.
> 
> API v2 has instead a set_rd_bit. Documentation
> <https://atlas.ripe.net/docs/api/v2/reference/#!/measurements/Measurement_List_POST>
> does not indicate its default value.

You're right, the reference doesn't indicate a default value (we will
fix that), but it should be "false", with the exception of when using
the probe's own resolver as you mentioned above. This behaviour is still
documented in the manual:
https://atlas.ripe.net/docs/api/v2/manual/measurements/types/type_specific_attributes.html

> Anyway, my experience with the API is that the RD (Recursion Desired)
> bit is always set, whether with 'set_rd_bit': False or with
> 'set_rd_bit': True, and independant of use_probe_resolver.
> 
> I can understand this choice for privacy reasons (RFC 7626, section
> 2.3). But, in that case, the documentation should be fixed.
> 
> Anything I missed?
> 
> (Here, a request by a probe, the + after the Query ID - here, 52379 -
> means the RD bit is set
> 
> 12:22:23.170304 IP (tos 0x0, ttl 64, id 2287, offset 0, flags [DF], proto UDP (17), length 65)
>     192.168.2.8.45955 > 212.27.40.240.53: [udp sum ok] 52379+ AAAA? uucp.bortzmeyer.org. (37)

It looks like this corresponds to measurement ID 8756383, which indeed
has set_rd_bit set which is reflected in the answer found in the abuf.

However, I notice that you also created a measurement #8756385 which
does not have set_rd_bit to true in the metadata, nor is RD reflected
in the results -- did you create this measurement in a different way?

Regards,
Chris Amin
RIPE NCC

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