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I am personally interested in who and/or how website/HTTP blocking is done in the case of this question: How is my ISP blocking my DNS query if I'm using DoH (DNS-over-HTTPS)? As I mentioned as comment, while DNS blocking is done as well, using DoH, clients do get the correct IP, and still cannot connect to/get unexpected/invalid responses from the correct/intended host.

It was closed as OOT, but I could not find a better fitting StackExchange site, looking through all of them. Does someone have a suggestion, where to ask it instead?

I did quite a lot of investigation with the user who asked it, and since we by times deal with network/internet related issues of users, it would be very helpful to know which actor is performing these blocks, and how it is technically done. That way we can better detect/help/inform about similar cases, and the matter in general raises security/privacy concerns, if the ISP or other actors on the route perform HTTPS inspection.

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    The linked question asks questions we cannot answer: “How is my ISP snooping on my query over DoH? Did they reject the route somewhere when I sent out the query? Did I misconfigure somewhere within my network?” We cannot figure out how an ISP does things; the user’s experience could be flawed and based on a misconfiguration issue. I think your question can be answered as long as it is an answerable concept and not a “Why did my ISP do this?” question. May 11 at 17:52
  • True, the question should maybe have been phrased differently. Ways to debug/investigate it (traceroute/mtr now that I think of it), and maybe some technical background about possibilities ISPs have, would have been interesting, but I am also not sure whether this would have lead to anything productive. However, at least one part of the issue turned out to be a HTTPS filtering/inspection by the AdGuard app, which is enabled by default. Obviously it blocked the affected websites. But also a headless Linux system got weird answers, despite DoT, so it was not everything.
    – MichaIng
    May 12 at 13:08
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    @MichaIng - It’s never too late to reword a question
    – Ramhound
    May 15 at 1:09

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