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Cloudflare DNS cached

will phinney 21 Reputation points
2020-10-29T18:43:58.247+00:00

Good afternoon everyone! I was asking some questions about DNS caching a while back and was wondering if anybody had any input on this. If my DNS caching is set for 1 day, default, and my public DNS entry goes down, but it's still cached at my server, why would't I be able to reach it?

For example,
example244928.com----->(CNAME Record) to LB in a public cloud.

If everything is still cached for a day why would I not be able to reach it even though the public record is down.

Thanks!

Windows DHCP
Windows DHCP
Windows: A family of Microsoft operating systems that run across personal computers, tablets, laptops, phones, internet of things devices, self-contained mixed reality headsets, large collaboration screens, and other devices.DHCP: Dynamic Host Configuration Protocol (DHCP). A communications protocol that lets network administrators manage centrally and automate the assignment of Internet Protocol (IP) addresses in an organization's network.
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  1. Sunny Qi 11,031 Reputation points Microsoft Vendor
    2020-10-30T06:19:29.6+00:00

    Hi,

    Thanks for posting here.

    By default, Windows stores positive responses in the DNS cache for 86,400 seconds (i.e., 1 day) and stores negative responses for 300 seconds (5 minutes).

    If everything is still cached for a day why would I not be able to reach it even though the public record is down.

    If a web page has changed the location of its web server in the time since its IP address was cached, a web browser might return an HTML 404 error—although the site is still online, the cache is feeding the browser an inaccurate IP address. This blocks the user’s access to an active page. That's why the records were cached but you could not reach it, so cleaning the DNS cache regularly is important to ensure consistent access to web pages.

    I would like to suggest that run the following command via command prompt and then please check if you could reach out to the same website.

    ipconfig/fulshdns

    Best Regards,
    Sunny

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  2. will phinney 21 Reputation points
    2020-11-02T17:10:03.623+00:00

    @Sunny Qi Thanks for the reply! So you're saying b/c of a negative DNS response it can no longer query the site b/c the CDN is down, so it then flushes it?

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