[atlas] What is the meaning of 127.0.0.1 as probe resolver?

On 13/10/2017 19:19, Baptiste Jonglez wrote:

Hi Baptiste,

> While looking at the result of built-in DNS measurements that use the
> probe resolvers, I noticed that a significant fraction of probes have
> "127.0.0.1" as a resolver.  And the results are strange: performance is
> really bad, for instance measurement 30002 gives a median resolution time
> of 300 ms for these probes!
> 
> What could be the meaning of this?  It almost looks like a recursive
> resolver with no cache at all is running on the probes themselves.
> 
> I was looking at this measurement: https://atlas.ripe.net/measurements/30002/
> 
> And here are some example probes that exhibit this "127.0.0.1" symptom:
> 6001, 6087, 6162, 6235, 6308.

All these probes are actually RIPE Atlas anchors. They all run a caching
recursive resolver, which can, and often is, used to perform DNS lookups
for measurements running on these anchors.

The high latency in resolution could be for any number of reasons, so I
can't immediately it.

Regards,
Anand Buddhdev
RIPE NCC

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