If a site will not resolve, first find out whether the failure is limited to one device, one network, one domain, or a DNS record type. Then query the intended resolver and read its response before changing settings: a timeout, NXDOMAIN, SERVFAIL, and a wrong address point to different causes. This guide covers Windows client checks and the DNS-server and security issues that may require an administrator.
1. Scope the failure before changing DNS settings
Record the exact domain, time, full error text, device and network, configured DNS server, and any recent changes to records, nameservers, VPN settings, router configuration, or security policy. Browser messages such as “DNS_PROBE_FINISHED_NXDOMAIN” describe what the browser observed; they do not, by themselves, establish the root cause.
- Does the problem affect one device or every device on the network?
- Does it affect one domain or many?
- Does it happen on one network or also on another connection?
- Is a particular application or record type involved?
Compare with a working device or network if available, while following any workplace policy about which resolvers you may use. Microsoft’s guidance divides DNS problems into client-side and server-side issues and recommends starting on the client side unless the scope points to the server (Microsoft Learn: Troubleshooting DNS Servers; Microsoft Learn: Troubleshooting Domain Name System (DNS) issues).
2. Check client configuration and query the intended resolver
On Windows, inspect the address, subnet mask, default gateway, and DNS server shown by ipconfig /all. Then query a named resolver directly:
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Replace the example domain and placeholder with the actual name and resolver IP. Record the full response and repeat the query for a known-working domain if appropriate. A successful ping to an IP address does not prove DNS works: it tests a different layer.
On Windows, nslookup normally sends DNS queries over UDP port 53. A timeout can result if a firewall or network filter blocks DNS, the server is not reachable, the DNS service is stopped, or the server is not listening on the interface being queried. Microsoft’s troubleshooting guidance also covers server interfaces, recursion, delegation, reachability, and event logs (Microsoft Learn: Troubleshooting DNS Servers).
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3. Interpret the result before choosing a fix
| Observed response | What it indicates | What to investigate |
|---|---|---|
| Timeout or no response | The query did not receive a usable reply from the resolver. | Check resolver reachability and service state, listening interface, and firewall or network rules for DNS. Confirm the client is querying the intended server. |
| NXDOMAIN | The resolver reports that the queried name does not exist. | Check spelling, the intended zone, record presence, and delegation. After a recent change, account for negative caching; RFC 9520 describes caching of DNS resolution failures (RFC 9520). |
| NOERROR, but no desired address | The query succeeded, but the requested record type may not contain the address or data the application needs. | Check the requested type and published data. A domain can have an A record but no AAAA or MX record, for example. |
| SERVFAIL | The resolver could not complete the lookup. | Check upstream reachability and resolver logs. If the domain uses DNSSEC, test whether validation is failing; SERVFAIL is not proof of a DNSSEC problem. |
| Wrong or stale address | A resolver returned data that differs from the expected current answer. | Compare the authoritative answer with the recursive resolver’s answer, and review TTLs, recent changes, and whether the resolver is the one intended. |
4. Clear only the cache that may be stale
A client cache flush clears only that client’s cache. On Windows, run:
ipconfig /flushdns
For a Windows Server, Microsoft distinguishes the DNS client cache from the cache maintained by the DNS Server service. Use Clear-DnsClientCache for the client cache or Clear-DnsServerCache for the DNS Server service cache, as appropriate to the problem and your access level (Microsoft Learn: Troubleshooting DNS Servers).
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After clearing a cache, repeat the same query to the same resolver to see whether that layer changed. A client flush cannot purge caches held by third-party recursive resolvers. Those may continue serving cached positive or negative results until their applicable TTL or negative-cache period expires; use a provider’s cache controls if available.
5. Verify authoritative records and nameserver delegation
If you administer the domain, confirm that the registrar delegates it to the nameservers currently hosting its zone. Then check that the record is in the correct zone and has the intended name, type, target, and TTL. A nameserver migration can leave an old delegation or DNSSEC security record in place.
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If the authoritative answer is wrong, flushing a device cache will not fix it. Correct the record at the authoritative DNS host, verify delegation at the registrar, and query again. For recent changes, distinguish stale cached answers from incorrect authoritative data by checking both layers rather than relying on one recursive lookup.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.6. Investigate DNSSEC when validated lookups return SERVFAIL
For a DNSSEC-signed domain, a mismatch between the DS record at the registrar and the DNSKEY data at the authoritative provider can break the chain of trust. This can happen, for example, when nameservers change but old DS data remains. Cloudflare documents a diagnostic using dig and +cd to check whether data is returned when DNSSEC checking is disabled (Cloudflare: Troubleshooting DNSSEC).
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If an ordinary validated lookup returns SERVFAIL but a query with checking disabled returns data, treat that only as evidence to investigate DNSSEC configuration—not as proof that the unchecked answer is authentic. Correct the DS/DNSKEY configuration with the registrar or authoritative provider, or restore a valid signed chain. Do not leave DNSSEC validation disabled as the lasting fix. RFC 9520 also notes that DNSSEC validation failures can be cached, so a resolver may temporarily continue returning a cached failure after the underlying configuration is corrected (RFC 9520).
7. Treat encrypted DNS as a transport choice, not a universal repair
DNS over HTTPS (DoH) and DNS over TLS (DoT) encrypt DNS transport. They do not create missing records, correct delegation, or repair a broken DNSSEC chain. On a managed network, switching to an unapproved upstream resolver can also bypass organizational filtering and policy. CISA’s memo discusses this trade-off for federal networks; it is federal-agency guidance, not a universal recommendation for every home or organization (CISA: Addressing DNS Resolution on Federal Networks Memo). CISA also encourages encrypted communications (CISA guidance on communications infrastructure).
For Windows Server DoH deployments, Microsoft’s troubleshooting checklist includes service state, endpoint URI, certificate trust, client connectivity, firewall access to the configured TCP port, and upstream resolution (Microsoft Learn: DNS over HTTPS (DoH) client support). A failed DoH setup should be investigated at those points rather than treated as evidence that ordinary DNS records are broken.
8. Review LLMNR as a separate local security issue
Link-Local Multicast Name Resolution (LLMNR) is a Windows name-resolution mechanism that may be used when DNS is unavailable or fails. CISA warns that LLMNR poisoning can enable man-in-the-middle activity and credential harvesting. Disabling it is an administrator security-hardening decision, not a routine end-user repair for a failing website.
Administrators should inventory dependencies and test applications before disabling LLMNR; CISA cautions that software relying on it may be disrupted. Where it cannot be disabled, consider network segmentation (CISA: Disable Link-Local Multicast Name Resolution (LLMNR) Service (CM0053)).
Quick Recap
When to escalate
- Home user: If one device fails, collect its
ipconfig /alloutput and resolver response, then check its local network settings and cache. If all devices fail, contact the network or DNS provider with the exact domain, time, and response. - Domain owner: If authoritative data or delegation is wrong, correct it with the registrar or DNS host. If validated queries return SERVFAIL for a signed zone, have the DNSSEC chain checked before changing client settings.
- Network administrator: Check resolver service and logs, interface bindings, upstream reachability, firewall policy, approved encrypted-DNS endpoints, and local fallback mechanisms. Preserve required organizational filtering and test security changes for application compatibility.
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