DNS Glossary
Short, plain-English definitions of the DNS terms you'll bump into when troubleshooting propagation, mail authentication, or DNSSEC. Cross-linked with the WhereIsDNS lookup tools so you can move from definition to verification in one click.
Caching and propagation
Why a record change is live in one place and stale in another, and how long that lasts.
- TTL (Time To Live): What TTL means in DNS, how resolver caches use it, common values, and how to plan a DNS change around TTL.
- DNS Caching: How and where DNS records are cached, and why caching is the root cause of "DNS propagation" delays.
- NXDOMAIN: What NXDOMAIN means in DNS, why you might see it, and how it differs from NODATA and SERVFAIL.
How a lookup resolves
The machinery between typing a name and getting an address back.
- Recursive Resolver: The difference between recursive resolvers and authoritative nameservers, and why it matters for DNS troubleshooting.
- DNS Zone: What a DNS zone is, how zones are delegated, and the role of the SOA record at the zone apex.
- GeoDNS: How GeoDNS returns different answers based on the resolver's location, and how to verify it's working as expected.
- Anycast: What anycast is, how anycast DNS resolvers work, and why 1.1.1.1 and 8.8.8.8 are everywhere.
Authentication and integrity
Proving an answer really came from who it claims — for DNS records and for mail.
- DNSSEC: How DNSSEC adds cryptographic verification to DNS, the role of DNSKEY and DS records, and what "secure delegation" means.
- SPF: What SPF (Sender Policy Framework) is, how it's published as a TXT record, and how it interacts with DKIM and DMARC.
- DKIM: How DKIM cryptographically signs outgoing email, where the public key lives in DNS, and how to look it up.
- DMARC: How DMARC ties SPF and DKIM together, what "alignment" means, and how to read a DMARC policy record.