1. Record the failing hostname, application error and time. Distinguish a complete domain name from a short internal name.
2. Run ipconfig /all and inspect the active network adapter's addresses, gateway, DNS servers and connection-specific suffix. Compare them with the intended network configuration.
3. For a domain-joined server, verify the approved internal DNS design. Replacing its resolvers with arbitrary public servers can prevent resolution of the organisation's internal directory records.
4. Query the failing complete name, for example nslookup www.example.com.. The trailing dot makes the fully qualified name explicit. Record which DNS server answered and the returned result.
5. Compare a known working internal or external name where relevant. This helps separate one missing record from a resolver or network-path failure.
6. If the complete name works but the short name fails, inspect the DNS suffix configuration. If every query times out, investigate access to the configured resolver rather than changing the website's DNS records first.

Use ipconfig /displaydns to inspect the local resolver cache. After confirming that the authoritative problem is corrected, ipconfig /flushdns clears that client's cached answers, including negative results. It does not clear every resolver on the internet.

Nslookup does not use the Windows client's DNS cache, so a successful query can differ from an application's cached result. Also check an intentional Hosts-file entry and whether the application maintains its own cache. Investigate the specific layer before repeatedly flushing unrelated caches.

Once the name returns the expected address, test the intended connection, certificate and application response. Correct DNS resolution does not prove that a web server or database listener is available at that address.

Run this in PowerShell on the Windows machine experiencing the lookup failure. Replace the sample name with the exact fully qualified hostname. The trailing dot avoids interpreting the name relative to an unintended DNS suffix.

Get-DnsClientServerAddress
Resolve-DnsName -Name 'www.example.com.' -Type A -DnsOnly
Resolve-DnsName -Name 'www.example.com.' -Type AAAA -DnsOnly

Read the result: Compare the active adapter's configured resolvers and the returned records with the expected internal or public DNS design. A name can have A records without AAAA records, so an absent AAAA answer is not automatically an outage. A timeout differs from a valid response reporting that the name does not exist.

For a domain-joined server, preserve the approved internal DNS configuration. Test the actual application connection after resolution succeeds. Repeated cache flushing cannot fix an absent authoritative record or a network path that cannot reach the configured DNS server.

• Diagnosing a Windows Server RDP connection failure
• Verifying Windows Server time synchronization
• Creating an IIS website with the correct bindings
• Creating a narrowly scoped Windows Firewall rule

• Microsoft: troubleshoot DNS clients
• Microsoft: configure Windows Server with SConfig

• Microsoft: Resolve-DnsName