IP to ASN Lookup
Enter any IPv4 or IPv6 address to identify the Autonomous System Number (ASN) that owns it. The lookup queries live BGP routing tables and returns the ASN, network owner, ISP, and the regional internet registry that allocated the block — ARIN, RIPE, APNIC, LACNIC, or AFRINIC.
Useful for threat investigation, network reconnaissance, email source identification, and routing analysis. Both IPv4 (e.g. 8.8.8.8) and IPv6 (e.g. 2001:4860:4860::8888) are supported.
What Does an IP to ASN Lookup Return?
When you enter an IP address, the lookup queries the global BGP routing table — the distributed database that every internet router uses to forward traffic. The result maps your IP to the Autonomous System that announces it, along with:
- ASN: The unique identifier assigned to that network (e.g. AS15169 for Google, AS13335 for Cloudflare, AS16509 for Amazon AWS).
- AS name: The registered short name of the network operator.
- Organisation: The legal entity that owns the AS block.
- ISP: The internet service provider, which may differ from the org name for large networks.
- Registry: The RIR that allocated the block: ARIN (North America), RIPE (Europe/Middle East), APNIC (Asia Pacific), LACNIC (Latin America), or AFRINIC (Africa).
- IPv4/IPv6 route counts: The number of IPv4 and IPv6 prefixes announced by that ASN.
- Type: The network classification: ISP, BUSINESS, HOSTING, etc.
Common Use Cases
Threat Intelligence and Incident Response
When investigating a suspicious IP in server logs or a SIEM alert, IP to ASN lookup is the first step. Identifying the owning network — whether it's a known cloud provider, a residential ISP, a VPN exit node, or a hosting company with a poor reputation — immediately contextualises the risk.
Email Source Verification
Spam and phishing analysis routinely involves checking whether the sending IP's ASN matches the claimed sender domain. A message claiming to be from a Fortune 500 company but originating from an ASN registered to a residential ISP is a strong indicator of spoofing.
Network Reconnaissance and OSINT
Security researchers and penetration testers use IP to ASN lookups to map an organisation's IP infrastructure — identifying the owning AS is the first step toward understanding the scope of an organisation's internet presence.
CDN and Hosting Identification
Determining whether an IP is served by AWS (AS16509), Cloudflare (AS13335), Google Cloud (AS15169), or Azure (AS8075) is essential for routing decisions, WAF configuration, and infrastructure fingerprinting.
IPv4 vs IPv6 in ASN Lookups
Both IPv4 and IPv6 addresses map to ASNs through the same BGP mechanism, but there are practical differences.
IPv4 addresses (e.g. 203.0.113.47) are 32-bit numbers. IPv4 space is fully allocated — every public IPv4 address belongs to a registered ASN.
IPv6 addresses (e.g. 2001:4860:4860::8888) use 128-bit addressing. IPv6 deployment is uneven — major cloud providers and modern ISPs announce IPv6 prefixes aggressively, while others have not yet adopted it. If an IPv6 lookup returns no result, the address may be in an unannounced block.
An ASN can control both IPv4 and IPv6 prefixes simultaneously, and both are searchable with this tool.
What is an Autonomous System?
The internet isn't one giant network. It actually consists of many smaller networks that are connected to one another. These smaller networks get the name autonomous system, also can be called AS.
Think of an AS like a neighborhood in a city. Each neighborhood has its own streets and management. Similarly, each AS has its own IP addresses and routers managed by one organization. Your internet service provider runs an AS. Amazon runs one for AWS. Google has one. Universities and big companies have them too.
The word "autonomous" means independent. The organization running an AS controls how it operates. They decide routing policies, which networks to connect with, and how traffic flows through their infrastructure.
What is an ASN?
Every AS needs a unique identification number which is called is the autonomous system number or ASN for short.
Regional internet registries assign these numbers to make sure no duplicates exist. The five registries are ARIN (North America), RIPE (Europe/Middle East), APNIC (Asia Pacific), LACNIC (Latin America), and AFRINIC (Africa).
ASNs are written with "AS" in front, like AS15169 for Google or AS7922 for Comcast. The original format was 16-bit (numbers 1 to 65,535). As the internet grew, 32-bit ASNs were introduced, extending the range to over 4 billion possible numbers.
How IP Addresses Connect to ASNs
Every IP address belongs to an ASN. When an organization gets an ASN, they also receive IP address blocks called prefixes.
A prefix like 203.0.113.0/24 contains 256 individual IP addresses. The organization decides how to use them for their own infrastructure, customer assignments, or future expansion.
Large networks manage hundreds of prefixes. They accumulate these blocks over time through new allocations, acquisitions, or geographic expansion.
When you look up an IP address with our tool, we check BGP routing tables to find which ASN announces that IP. This tells you who owns and controls that address. It's like reverse phone lookup, but for internet infrastructure.
FAQs
An IP to ASN lookup starts with an IP address and returns the ASN that controls it — useful when you have an IP and need to identify the network owner. An ASN lookup works in the opposite direction: you provide the AS number and retrieve everything registered under it — all IP prefixes, BGP peering relationships, WHOIS contact details, and upstream/downstream routing data. If you already have an ASN (e.g. AS13335), use the ASN Lookup tool for the full network picture. If you have an IP and need to find its ASN first, start here.
Bogon addresses are IP ranges that are not part of the public internet routing table. These include:
- Private ranges:
10.0.0.0/8,172.16.0.0/12,192.168.0.0/16 - Loopback:
127.0.0.0/8 - Link-local:
169.254.0.0/16 - Reserved and unallocated blocks defined by IANA
Because bogon addresses are never announced via BGP, they have no ASN assignment. Querying one will return no result — this is expected behaviour, not an error.
This tool processes one IP address per query. For bulk lookups — resolving ASN and geolocation data for thousands of IPs in a single request — use the Bulk IP Lookup API. It accepts up to 50,000 IPs per request and returns structured ASN, ISP, country, and city data for each. No scraping, no per-IP rate limits on paid plans.
IPv4 prefixes use the traditional 32-bit address format (e.g. 192.0.2.0/24 — a block of 256 addresses). IPv4 space is fully exhausted at the registry level; all new allocations come from existing holders transferring blocks.
IPv6 prefixes use 128-bit addressing (e.g. 2001:db8::/32). The address space is functionally inexhaustible. In an ASN record, IPv4 and IPv6 prefix counts are listed separately because they are announced via different BGP address families (AFI 1 for IPv4, AFI 2 for IPv6).
Enter the IP address in the field above and press "ASN Lookup." The tool queries live BGP routing tables and returns the ASN within seconds. No account required.
For programmatic lookups, use the IP Geolocation API:
GET https://api.apifreaks.com/v1.0/geolocation/lookup?ip={IP}&apiKey=YOUR_KEYThe response includes the ASN number, AS name, organisation, network type, RIR, and the number of IPv4 and IPv6 routes announced by that ASN. To retrieve the actual IP block the address belongs to, use the IP WHOIS API. To retrieve the full list of route prefixes and BGP peer data for that ASN, pass the AS number to the ASN Lookup API.
Yes. The IP Geolocation API returns the ASN, AS name, organisation, network type, RIR, and IPv4/IPv6 route counts for any IPv4 or IPv6 address. For high-volume use cases, the Bulk IP Lookup API processes up to 50,000 IPs per request with the same response structure.
For the actual IP block and address range an IP belongs to, plus full organisation and abuse contact details, use the IP WHOIS API. For the complete list of route prefixes and BGP upstreams, peers, and downstreams for an ASN, use the ASN Lookup API.
Both APIs are available on a free tier (10,000 credits, no credit card required) with paid plans for higher volumes.