Diagnosing DNS Problems When a Site Will Not Resolve

Before assuming something complicated is wrong, confirm the basics. Run the domain through a DNS Lookup and see whether it returns an A or AAAA record at all. A surprising number of reported outages turn out to be a typo in the domain name, or a record that was simply never created.

• NXDOMAIN means the name server was reached and it explicitly says this domain does not exist. This usually points to an expired registration, a typo, or a domain that was never registered in the first place.
• An empty answer with no error means the domain exists and the name server responded, but there is no record of the type you asked for. A domain can validly have an A record but no AAAA record, for example.
• A timeout means no name server answered at all within a reasonable time. This points at the authoritative name servers themselves being unreachable, misconfigured, or the domain's NS delegation pointing somewhere that no longer exists.

If a change was made recently and only some people are seeing it while others still land on the old server, this is almost always caching rather than a fault. Different resolvers around the world hold onto answers for as long as the TTL allows, so someone whose resolver just refreshed will see the new value while someone whose resolver cached the answer five minutes before the change will not, sometimes for hours. This resolves itself with time and does not usually need any further action. Running the domain through the DNS Propagation tool shows directly whether major public resolvers already agree, rather than guessing from what any one person happens to see.

A domain's registrar and its DNS provider are not always the same company, and it is easy to update records in the wrong dashboard entirely. Look up the domain's NS records and compare them against what your DNS provider actually told you to use. If they do not match, every change you make in your current dashboard is invisible to the rest of the internet, because the domain is still delegated somewhere else.

A domain that suddenly stops resolving with no recent changes made to it is frequently a lapsed registration, particularly if it was set up years ago and the renewal email went to an inbox nobody checks any more. A WHOIS lookup will show the expiry date and current registration status directly, which settles this possibility quickly rather than leaving it as a guess.

1. Confirm the domain spelling and run a DNS Lookup for A, AAAA and NS records.
2. Note whether the result is NXDOMAIN, an empty answer, or a timeout.
3. Check the NS records match your actual DNS provider.
4. Run a WHOIS lookup to rule out an expired registration.
5. If only some visitors are affected, wait out the TTL before assuming anything is broken.