[atlas] Tagging probes which are using the ISP's DNS server?
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Daniel AJ Sokolov
listclient at sokolov.eu.org
Thu Oct 6 07:41:59 CEST 2022
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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