What is RDAP?

RDAP (Registration Data Access Protocol) is the successor to whois, returning registration data for IPs, ASNs and domains as JSON over HTTPS.

Classic whois sends a line of text to TCP port 43 and gets free-form text back, in a different layout from every registry, which makes it hard for software to parse. RDAP uses ordinary web requests instead. The query is a URL path, such as /ip/192.0.2.1, /autnum/64500 or /domain/example.com (RFC 9082), and the answer is JSON with standard fields for the holder, contacts, status, events like registration dates, and links to related objects (RFC 9083). Bootstrap files published by IANA say which registry's RDAP server is responsible for each address block, ASN range and top-level domain, so a client can find the right server without hard-coded lists. Because it runs over HTTPS, it can also support authenticated, tiered access to data that shouldn't be public.

All five Regional Internet Registries run RDAP services for number resources, and generic top-level domain registries and registrars now offer it too, so for "who holds this address?" or "who owns this domain?" RDAP is increasingly the main source, and many tools use it behind the scenes. The thing to know for routing work is what RDAP doesn't cover: route objects, as-sets and other IRR data are still queried with whois, or with IRRd's own query language, and filter tools like bgpq4 use those. An RDAP answer about an address range is registration data, the equivalent of an inetnum, and says nothing about where the range is routed. The IRR, RPSL and AS-SETs lesson covers the whois queries used for routing data.