DNS_PROBE_FINISHED_NXDOMAIN but only with some ISP

I have a website (https://rocketscience.com.br) that is displaying the error DNS_PROBE_FINISHED_NXDOMAIN but only with some internet service providers. For the people that use “Claro” for example, the site is working fine. But if someone uses “Vivo” the site exhibits the error mentioned. The problem is cross-device and general (affect all users) for each ISP. I checked with the ISPs if they are blocking my domain and they confirmed that they are not. I checked with Hostinger, and they said that the problem is with Cloudflare. I double-checked the DNS registries to make sure everything was configured correctly and everything seemed fine. I have no idea what is causing this issue. Can someone shed some light into this problem?

Vivo, or “Telefônica Vivo” seems to be a trading name of “Telefônica Brasil”.

Conducting a couple of tests from AS26599 Telefônica Brasil, it appears that the DNS resolution for the domain you mention returns the “NXDOMAIN” error, no matter if we’re taking the naked domain, or the www variant.

However, when trying the DNS query through other resolvers, such as e.g. Google’s 8.8.8.8 resolver, but still done via the AS26599 Telefônica Brasil network, the domain is resolving just fine.

Based on what I see, I’m sceptical about that confirmation.

  1. What AS number(s) are you seeing the problem from?
    The AS number can be found here:

A “DNS” test through jsdelivr.com/globalping when you choose “Brazil” as the location, seems to be coming to the same conclusion as I did above.

Hit CTRL+F, and input “NXDOMAIN” in the search field.

All networks named “Telefônica Brasil”, even across different AS numbers, are all returning “NXDOMAIN”.

So it is a problem that needs to be found and remediated within “Telefônica Brasil”.

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