Reference
DNS, WHOIS and ASN Reference
A lookup reference for DNS record types and TTLs, resolver propagation, WHOIS and RDAP registration fields, and autonomous-system numbers.
DNS stores records that map a name to addresses, aliases, mail exchangers, text values and name servers. A resolver answers a query and caches the result for the record's TTL, which is why a recent change can appear on some resolvers before others. WHOIS and RDAP expose registration data, and an autonomous system number identifies the network that advertises an IP prefix.
01Quick reference
- A and AAAA map a name to IPv4 and IPv6 addresses; CNAME makes a name an alias of another.
- MX carries a preference number and a mail host; a lower preference is tried first.
- TXT carries SPF, DKIM and verification strings; values are free-form text, not structured proofs.
- NS lists the authoritative name servers for the zone.
- TTL is the cache lifetime in seconds; propagation reflects resolver caches expiring.
- WHOIS uses port 43 and is unauthenticated; RDAP is its JSON, HTTPS successor.
- An ASN identifies the network advertising a prefix; BGP carries those announcements.
02Limitations
This reference summarises the standards; it is not a substitute for the full RFCs and omits DNSSEC, zone transfer, registry-specific WHOIS fields and long-run routing history.
Frequently asked questions
- Why does a changed record appear on only some resolvers?
- Resolvers cache answers for the record's TTL. Until each cache expires and re-queries the authoritative servers, a freshly changed record can differ between resolvers.
- Is WHOIS being replaced?
- RDAP is the structured, HTTPS-based successor to WHOIS and is being deployed by registries and registrars, but WHOIS remains in use. The lookup tool normalizes whichever the configured provider returns.
Sources
- RFC 1034: Domain names - concepts and facilities — IETF (accessed 2026-10-05)
- RFC 1035: Domain names - implementation and specification — IETF (accessed 2026-10-05)
- RFC 3912: WHOIS protocol specification — IETF (accessed 2026-10-05)
- RFC 7483: JSON responses for the Registration Data Access Protocol (RDAP) — IETF (accessed 2026-10-05)
- RFC 4271: A Border Gateway Protocol 4 (BGP-4) — IETF (accessed 2026-10-05)