The browser says a server address cannot be found? DNS translates names into addresses; network connectivity, TLS and the web server must then also work. This Windows 11 guide collects useful evidence before changing DNS servers or router settings.
Record the scope
Note time with time zone, exact hostname and complete error. Check whether one website or several unrelated sites fail and whether a second device on the same network shows the same problem. A working cellular connection is a comparison over another network, not proof of a broken router. Keep the required connection state for a VPN or corporate access.
Read the configuration
Open Command Prompt and run ipconfig /all. Find the LAN, Wi-Fi or VPN adapter actually in use and note addresses, default gateway and DNS servers. Do not use a disconnected adapter’s entry. Resolve missing connectivity or unsuitable network configuration first. A ping timeout alone does not prove an outage because ICMP may be blocked. Do not publicly share complete output containing internal names and addresses without review.
Query the exact name
Replace www.example.com. below with the affected complete hostname. Do not include https:// or a path; the final dot prevents appended search suffixes.
nslookup -type=A www.example.com.
nslookup -type=AAAA www.example.com.Record the DNS server actually queried and its answer. A is IPv4, AAAA is IPv6. A missing AAAA record is not automatically an error for an IPv4-only site.
- Addresses returned: This DNS query received an answer; it does not yet prove website availability or a correct answer for every application.
- Nonexistent domain/NXDOMAIN: The queried resolver reports that the name does not exist. Check spelling; internal names, split DNS or filtering may require a different responsible resolver.
- Timeout: No timely answer arrived. Distinguish resolver reachability, connectivity and filtering.
- Server failure/SERVFAIL: The resolver could not return a valid answer. That differs from saying a name does not exist.
Assess DNS and browser separately
nslookup does not reproduce the entire Windows or browser resolution path. Windows considers cache and the Hosts file, among other things; a browser may use its own secure DNS. For differing browser results, record that setting and compare with a second browser without indiscriminately disabling security. Opening a bare IP address is not an equivalent HTTPS test: certificates and virtual websites need the hostname.
Escalate with evidence
Give responsible support the hostname, time, affected devices, connection type, queried resolver and exact results. Do not send internal corporate names to public resolvers or replace managed DNS settings with arbitrary providers. Clearing a cache fixes neither an unreachable server nor incorrect authoritative DNS data. Make a suitable reversible correction only after narrowing down the cause, then repeat the same tests.