On this topic: Is there an Atlas-preferred setting for this? Should the
probe I host ideally use the ISP's DNS, or ideally a DNS from a global
player? Or ideally an academic/non-profit DNS?
BR
Daniel AJ
On 10/5/22 18:38, Max Grobecker wrote:
Hi,
a few days ago I wanted to debug a name resolution problem of one of our
domains.
For this reason, I wanted to test if probes inside a specific ASN are
having difficulties to resolve a specific name (because only customers
of this ISP were complaining).
This lead to very mixed results, mostly because some of the selected
probes did queries to a public DNS service like Google, Quad9 and so on.
The problem existed only with the provider's DNS servers for some reason.
It did take some time to make a script which tried to filter out these
probes, so I wondered if anyone else had the same use-case and problem.
Is there a way to automatically tag probes, which are (seemingly) using
the ISP's own DNS servers, or, at least, not a well-known public service?
This could be done maybe by querying a special DNS name which returns
the IP address from where the query was received (like
"whoami.akamai.net").
By comparing the ASN of the probe and the ASN of the IP address returned
by the DNS query, one could determine, if the ISP's servers are used.
This would also be true for people running their own recursor, but this
could be filtered as well very easy.
If an ISP is using multiple ASN, this could be a problem. Maybe there's
an easy solution for this as well.
Probes which pass this test, could then be tagged with
"DNS-using-ISP-server" or something like that and explicitly be selected
for specific DNS resolution tests.
Greetings,
Max
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