DNS Resolution Failure

Demonstration lab (not a client case). A workstation appears to have internet connectivity, but websites do not load when typed by hostname.

Pages time out or show a "server not found" error by name. Reaching a known public IP address still works. Other devices on the same network may or may not be affected.

Unreachable or misconfigured DNS server; stale or poisoned local DNS cache; DHCP handing out an incorrect DNS server; a VPN or security agent overriding resolver settings; a hosts-file entry pointing a name at the wrong address.

Confirm raw IP connectivity first, then test name resolution separately, then inspect the resolver the adapter is actually using. If the IP address answers but the name does not resolve, the fault is in name resolution rather than in connectivity.

Clear the local resolver cache, then correct the resolver configuration: either renew DHCP so the adapter receives a valid DNS server, or set a known-good DNS server on the adapter. Remove any incorrect hosts-file entry found during diagnosis.

Resolve the same hostname again with nslookup and confirm an answer from the expected server, then load a site by name in the browser. Confirm that resolution still works after a reboot so the fix is persistent rather than cached.

If names still do not resolve: test with a second DNS server, test another device on the same network to separate host from network, check whether a VPN or endpoint security agent is enforcing its own resolver, review firewall rules for UDP/TCP 53, and escalate to the network team when the DNS server itself is unreachable.