RDAP versus WHOIS
Why structured RDAP is preferred and when a controlled WHOIS fallback is useful.
Definition and scope
Why structured RDAP is preferred and when a controlled WHOIS fallback is useful.
Use this reference to establish the meaning and limits of the result before changing production configuration.
How it works
RDAP returns structured JSON over HTTPS, supports bootstrap discovery and has explicit objects for domains, IP networks and autonomous systems. WHOIS is a plain-text TCP protocol whose fields and encoding vary between servers.
How to read it
RDAP events, entities, status arrays and links are machine-readable. WHOIS output must be interpreted as registry-specific text. Privacy redaction can appear in either system and does not mean registration is invalid.
Correct and incorrect examples
Compare the normalized examples. Technical values are illustrative and use documentation ranges or reserved names.
domain → IANA bootstrap → registry RDAP /domain/example.com?rdap_url=https://user.example/rdap| Element | Role | Example |
|---|---|---|
| RDAP | HTTPS JSON | IANA bootstrap |
| WHOIS | TCP 43 text | IANA referral |
| Domain | /domain/ | example.com |
| IP | /ip/ | 192.0.2.0 |
| ASN | /autnum/ | 13335 |
Common problems
Using a single hard-coded registry misses many TLDs and address ranges. Following arbitrary user-supplied servers creates security risk. Dates also vary in meaning: creation, last changed and expiration are separate events.
Practical checklist
Use IANA bootstrap, prefer RDAP, cap response size and time, identify the source, and use WHOIS only through an authoritative referral when RDAP is unavailable.
Standards and primary references
These primary specifications define the protocol behavior. Provider documentation may add operational requirements but cannot replace the standard.