How does DNS work, and how do you troubleshoot name resolution problems?

DNS translates names into IP addresses. When a client looks up a name:

• It checks its local cache, then the hosts file.
• It queries its configured resolver, which checks its own cache.
• If not cached, the resolver queries a root server, which directs it to the top-level domain servers, which direct it to the domain's authoritative name servers, which return the record.
• The result is cached for the record's TTL.

Record types: A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail servers), TXT (SPF, DKIM, verification), NS (authoritative servers), PTR (reverse lookup).

Troubleshooting, in order:

• Can you reach the IP directly? If yes, the problem is definitively DNS rather than connectivity.
• nslookup or dig against the configured server, then against a public one such as 8.8.8.8. A difference isolates it to internal DNS.
• Check the client's DNS settings with ipconfig /all or resolv.conf. A domain-joined machine pointing at a public resolver cannot resolve internal names — an extremely common misconfiguration.
• Flush the cache — ipconfig /flushdns — since stale entries persist after a record changes.
• Check the TTL if a record was recently updated. What people call propagation is really cache expiry.