[atlas] Effect of "Resolve on Probe"-option

On 2017-11-30 20:27, Tim Wattenberg wrote:
> Hi everyone,
> 
> I think I don’t quite understand the effect of the „Resolve on Probe“ option when creating a measurement. The form says it forces the probe to do DNS resolution, the API reference says that it indicates that a name should be resolved (using DNS) on the probe otherwise it will be resolved on the RIPE Atlas servers.
> 
> Could someone explain what this means for example if I have a simple measurement for querying the A record of a given domain via the probe’s resolvers?
> 
> Thanks, Tim

Hi,

When you measure something given with a DNS name and leave this option
to its default settings, then the DNS resolution happens once, in the
infrastructure (somewhere in Amsterdam, NL), and the probes are told to
measure towards the resolved *IP*. This is more efficient, prevents DNS
errors on the edges, but only works if DNS can only give one answer.

If you turn on "resolve on probe", then the probes get to measure the
*name* you entered, and do the DNS resolution themselves every single
time they measure. This has a somewhat higher chance of failure, but
it's needed if the resolved IP depends on the location of the vantage point.

Hope this helps,
Robert