[atlas] DNS measurement using the Probe's resolvers

On 2018/07/06 22:30 , Rami Al-Dalky wrote:
> I have a question about using the probe's list of resolvers when
> creating a DNS measurement. It is unclear to me whether the probe would
> send the query to all resolvers at the same time or not! Also, does the
> probe send the query to all resolvers in its list or to a subset of
> those resolvers? Is DNS eyeball implemented in the probes?

Hi,

The Atlas DNS measurement code sends one request at a time, in the order
in which the DNS resolvers are listed in /etc/resolv.conf on the probe.

In addition to measuring DNS, probe can also resolve a DNS name for the
target of a measurement. In that case, the stub resolver that is built
into libevent is used. That stub resolver does some clever and funky
stuff. I don't know the details of how DNS queries are scheduled.

Philip