ASN lookup egress environment
Who holds an AS number: special-purpose ASNs answered locally with their RFC, real ones fetched browser-direct from the owning RIR — with the registry named before anything is sent.
Nothing leaves the browser until you press Ask. Typing only computes, locally, what kind of number this is and which registry would be asked.
Routing is decided locally against a vendored copy of the IANA RDAP bootstrap (asn.json publication 2026-06-01, vendored 2026-07-08); special-purpose classification against the IANA Special-Purpose AS Numbers registry (accessed 2026-07-08). Live answers come from the registries themselves and carry no golden-vector guarantee.
An Autonomous System number identifies a routing domain on the internet, and five regional registries hold the records of who each one belongs to. This tool classifies your input locally, and only for globally-assignable numbers builds the one URL that would answer — the owning RIR's RDAP autnum endpoint — showing it to you before anything is sent.
Two whole classes of answer never touch the network: special-purpose numbers (AS0, AS112, AS_TRANS, documentation and private ranges, the two reserved ends of the space) are explained with their RFC right here, and numbers falling in bootstrap gaps are reported as unallocated. An honest tool refuses to pretend a lookup where none exists.
Sources: RFC 6793 · RFC 9082 · RFC 9083 · RFC 9224 (IANA bootstrap) · IANA Special-Purpose AS Numbers registry (2026-07-08) · data.iana.org/rdap (2026-07-08)