DNS checker

What does the DNS checker check?

It asks each resolver for one record type over DNS over HTTPS, then shows each answer and the TTL the resolver reports. The record types are:

• A: the IPv4 address of a name.
• AAAA: the IPv6 address of a name.
• CNAME: an alias that points one name at another.
• MX: the mail servers for a domain, with their priority.
• TXT: text records such as SPF, DKIM, DMARC and site verification codes.
• NS: the name servers that hold the domain’s DNS.
• CAA: which certificate authorities may issue SSL certificates for the domain.

Quad9 answers DNS over HTTPS only in the binary DNS format, which we found while building this tool. So the tool sends the same binary query to all three resolvers, and the answers compare like for like.

How do I read the result?

Green means every resolver that replied gave the same answer. Yellow means they disagree, or none of them found the record.

TTL is how many seconds a resolver keeps an answer before it asks again. Each resolver counts down from the moment it last fetched the record, so the three TTLs often differ. After you change a record, a resolver that still holds the old answer switches once its TTL runs out.

NXDOMAIN means the name does not exist at all. “No A record” means the name exists but has no record of that type.

Questions and answers

How long does a DNS change take to show everywhere?

It depends on the TTL of the old record. A record with a TTL of 3600 can stay cached for up to an hour after you change it. A name server change can take up to 48 hours, because the registry’s own record for the domain is often cached that long.

Why do I see a CNAME when I asked for an A record?

The name is an alias. Resolvers return the CNAME first, then the address it points to. The tool shows both.

Why does my CNAME not show for a site on Cloudflare?

When Cloudflare proxies a record (the orange cloud), public resolvers get Cloudflare’s own addresses as A and AAAA records instead of your CNAME. We saw this when we checked www.webstribe.com.

Does this check the DNS on my own computer?

No. It asks public resolvers. Your computer or office network may keep an old answer for longer. Wait for the TTL to run out or clear the DNS cache on your device.

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