Learn how IANA bootstrap data routes domain, IP and ASN queries to the correct authoritative RDAP service without guesswork.
What matters first
- Bootstrap maps a query object to an RDAP service before the object request is made.
- Domains, IP ranges and AS numbers use separate IANA registries.
- IP selection needs the most specific containing range.
- Clients should cache a known-good registry while respecting updates.
Domain bootstrap
The client extracts the final DNS label, converts it to its ASCII form when needed, and looks for that label in IANA's DNS bootstrap registry. The matching service URL becomes the base for a domain query.
The RDAP lookup applies this routing process to a domain or IP address and retains the responding source URL.
IP and ASN bootstrap
For an IP address, the client finds the most specific containing CIDR range in the IPv4 or IPv6 bootstrap registry. For an autonomous system number, it finds the containing numeric range. This directs the request to the relevant RIR service.
Cache without going stale
A production client should cache bootstrap files, honor HTTP validation signals, retain a known-good copy during a temporary outage, and periodically refresh. It should never silently route an unknown suffix to an unrelated provider.
For legacy referral behavior and its limitations, compare the same question with the WHOIS lookup.
Evidence-to-decision table
| Evidence | What it means | Responsible next step |
|---|---|---|
| DNS bootstrap | TLD label to service URL | Convert IDN suffix to ASCII first |
| IPv4/IPv6 bootstrap | Address range to service URL | Choose most specific containing range |
| ASN bootstrap | Numeric range to service URL | Validate AS number syntax |
| Service link | Base URL for RDAP query | Use HTTPS and correct object path |
Illustrative routing of three queries
This is an illustrative example, not a claimed real-world test.
For example.com, extract com and match the DNS bootstrap entry before appending the domain path.
For an IP address, parse it as a number and select the narrowest containing bootstrap range.
For an ASN, remove presentation prefixes such as AS only after validation, then match the numeric range.
Defensible outcome: The client reaches the service designated for each object class without guessing from branding, geography or a hard-coded list.
Action checklist
- Fetch from IANA
- Validate JSON before replacing cache
- Retain last known-good data
- Normalize object syntax
- Choose the correct registry
- Resolve overlaps deterministically
- Report unsupported objects clearly
Edge cases that change the answer
Multiple service URLs
Preserve ordering and fail over deliberately; do not merge responses as if they were one object.
Stale bootstrap cache
Expose refresh time and recover from temporary fetch failure with a known-good copy.
Unknown suffix
Return an unsupported or unbootstrapped result rather than sending the name to an unrelated operator.
Questions this guide should settle
Is bootstrap DNS resolution?
No. It discovers the RDAP service for registration data; it does not resolve website records.
Why not query a universal RDAP server?
Authority is distributed across registries, and bootstrap routes clients to the designated service.
Can a service redirect?
HTTP redirects may occur, but clients should apply safe redirect limits and preserve the final source.