ASN Lookup
Map a literal IPv4 or IPv6 address to the BGP origin network announcing its most-specific visible prefix, or inspect one ASN directly. Results preserve multi-origin answers and separate routing observations from registry metadata.
- IPv4, IPv6, ASPLAIN, and ASDOT input
- All observed origin ASNs preserved
- IANA special-use interpretation
- Authority, TTL, DNSSEC, and raw evidence
Run an ASN lookup
ASN lookup result
Lookup overview
Normalized input, query method, timing, and evidence completeness.
- Input
- Kind
- Origin ASN count
- Validated prefix count
- Completed
- Total browser time
- DNS queries
- Evidence state
Special-use and interpretation
Local classification is evaluated before the live lookup and kept separate from routing evidence.
What a Cymru answer means
Team Cymru publishes unfiltered observations from multiple BGP viewpoints. It can therefore return an origin for a bogon or special-use address if a partner sees a leaked or internal route. That does not make the address globally reachable.
BGP origin observations
Every parseable Team Cymru origin TXT value is retained; multiple ASNs are not collapsed into a single “winner.”
ASN registry metadata
Metadata is queried separately for each bounded origin ASN, so prefix registration and ASN registration remain distinct.
DNS evidence ledger
Per-query answer class, authority reachability, TTL evidence, analyzer cache, DNSSEC status, and partial-result markers.
Interpretation and limits
Evidence-based cautions for this exact result.
Raw evidence
Complete normalized bundle, Team Cymru TXT values, and Octetify analyzer responses used above.
Show raw JSON
Read the fields correctly
- Origin ASN is an AS observed announcing the matching BGP prefix.
- Prefix registry fields describe the address allocation; ASN fields describe the number registration.
- Team Cymru says country, registry, and allocation fields come from the RIRs; AS descriptions come from cidr-report.
- Allocation dates are registry dates, not route first-seen dates or freshness timestamps.
- Country codes are registry data, not device or user geolocation.
Multi-origin and no-answer cases
A prefix may legitimately have several origin ASNs because of multihoming, anycast, migration, or routing policy. This tool shows all origins reported. NXDOMAIN means the Cymru zone has no held mapping for the constructed name; NODATA, SERVFAIL, timeout, and partial evidence are reported separately and never converted into a fabricated “unrouted” verdict.
How the DNS mapping works
IPv4 octets are reversed into origin.asn.cymru.com. IPv6 is expanded to 32 hexadecimal nibbles and reversed into origin6.asn.cymru.com. ASN metadata uses AS<number>.asn.cymru.com. All are TXT queries.
Primary references: Team Cymru IP-to-ASN Mapping Service; IANA IPv4 Special-Purpose Registry; IANA IPv6 Special-Purpose Registry; IANA Special-Purpose ASN Registry; RFC 6890; RFC 5396 AS notation; and RFC 6996 private ASNs. Embedded classifications were reviewed against the registries on 2026-09-27; consult the live registries for later changes.