ASN Lookup - Find Network Owner, Registry & IP Prefixes
We don't store ASN queries or lookup results
Enter an ASN number or IP address to find organization details, announced prefixes, and network statistics.
Free AS Number Information Lookup
Enter an ASN to get started
View organization, prefixes, and network details
Look Up Any ASN for Organization & IP Prefix Data
ASN Lookup retrieves detailed information about an Autonomous System Number—a unique identifier assigned to networks that control their own routing on the internet. Enter an ASN like 15169 (Google) or an IP address to reverse-lookup which AS owns it.
What You'll Discover
Can Find
Cannot Find
How to Look Up an ASN
Find organization details and IP prefixes in seconds
Enter ASN or IP Address
Type an ASN number (15169 or AS15169) or any IP address (8.8.8.8) in the input field. We accept both formats.
Click Lookup
Press the Lookup button or hit Enter. Organization details appear within 2 seconds.
View Organization Details
See the ASN identity card showing organization name, country, registry, and registration date.
Browse IP Prefixes
The prefix table loads separately (may take 5-30 seconds for large networks). Filter by IPv4 or IPv6, paginate through results.
Understanding Your ASN Lookup Results
What each field tells you about the Autonomous System
ASN Number
The unique Autonomous System Number in format AS##### (e.g., AS15169). This identifier is used in BGP routing to identify the network.
AS15169
Organization Name
The company, ISP, or entity that operates this autonomous system. This is the official name registered with the RIR.
GOOGLE
Country
The country where the ASN is registered. Note: This is registration location, not necessarily where all IPs are used.
🇺🇸 US
Registry (RIR)
The Regional Internet Registry that allocated this ASN: ARIN (North America), RIPE (Europe), APNIC (Asia-Pacific), LACNIC (Latin America), or AFRINIC (Africa).
ARIN
Registration Date
When this ASN was first allocated to the organization. Older dates often indicate established networks.
2000-03-30
IPv4 Address Count
Total IPv4 addresses across all announced prefixes. Formatted as K (thousands), M (millions), or B (billions) for readability.
16.78M
IPv4/IPv6 Prefix Count
Number of CIDR blocks announced by this AS. More prefixes typically means a larger, more distributed network.
623 IPv4, 419 IPv6
Prefix Table
Each row shows a CIDR block (e.g., 8.8.8.0/24), its IP range, and address count. Paginated for large networks.
8.8.8.0/24 | 8.8.8.0 - 8.8.8.255 | 256
Key Features
Dual Input Mode
Enter an ASN number directly (15169 or AS15169) OR an IP address. IP inputs automatically reverse-lookup to find the owning ASN.
Split-Load Architecture
Organization details appear in under 2 seconds. Prefix data loads separately, so you're never waiting for everything.
Server-Side Pagination
Handle ASNs with 3,000+ prefixes without browser lag. Navigate through pages of 50 prefixes at a time.
IPv4/IPv6 Filtering
Filter the prefix table by IPv4 only, IPv6 only, or view all prefixes together.
Export to JSON/CSV
Download complete ASN data and prefix lists in JSON or CSV format for integration with your tools.
Free API Access
Query programmatically via our REST API. No registration, no API key required for standard usage.
When You Need ASN Lookup
Network Security Analysis
Identify what organization controls an IP address you've seen in logs. Useful for threat intelligence and blocking decisions.
Competitive Research
See how large a competitor's network is by checking their total IP addresses and prefix count.
Firewall Rule Planning
Get the complete list of IP prefixes for an ASN to create comprehensive allow/block rules.
Network Due Diligence
Verify when an ASN was registered and which RIR governs it before peering or transit agreements.
How ASN Lookup Works
Data Sources
We query RDAP servers from all five Regional Internet Registries (ARIN, RIPE, APNIC, LACNIC, AFRINIC) for authoritative ASN metadata. Prefix data comes from ipwhois ASNOrigin queries. IP-to-ASN mapping uses our local GeoLite2-ASN database for instant reverse lookups.
Split API Architecture
Phase 1 queries fast RDAP endpoints for organization info (0.5-2 seconds). Phase 2 enumerates prefixes via whois servers (5-30 seconds for large networks). This split approach means you see results immediately while comprehensive data loads.
Why Prefix Lookup Takes Time
Prefix enumeration requires querying whois servers that rate-limit responses. Large ASNs like Google (AS15169) have 1,000+ prefixes. We cache results for 1 hour to speed up repeat lookups.
Technical Specifications
- Data Sources
- RDAP, ipwhois, GeoLite2-ASN
- Update Frequency
- Real-time queries, 1-hour cache
- Phase 1 Response
- 0.5-2 seconds
- Phase 2 Response
- 5-30 seconds (large ASNs)
- Input Formats
- ASN (15169, AS15169), IPv4, IPv6
- Output Formats
- JSON, CSV export
- API Access
- REST API, no key required
Frequently Asked Questions
What is an ASN (Autonomous System Number)?
An ASN is a unique number assigned to an autonomous system (AS) by a Regional Internet Registry. An autonomous system is a collection of IP networks under the control of one or more network operators with a common routing policy. ASNs are used in BGP (Border Gateway Protocol) to exchange routing information. Valid ASN numbers range from 1 to 4,294,967,295.
What information does this ASN Lookup tool provide?
Our tool provides: the organization name operating the ASN, the country where it's registered, the registry (ARIN, RIPE, APNIC, LACNIC, or AFRINIC), the registration date, total IPv4 and IPv6 address counts, number of announced prefixes, and a complete paginated list of IP prefixes (CIDRs) with their address ranges.
Can I look up an ASN from an IP address?
Yes! Enter either an ASN number (like 15169 or AS15169) OR an IP address (like 8.8.8.8). When you enter an IP, we find which ASN announces that IP and show you all details about that autonomous system. This is called a reverse ASN lookup.
Why does the prefix list take longer to load?
ASN identity (name, country, registry) comes from fast RDAP queries taking 1-2 seconds. Prefix data requires querying whois servers which can take 5-30 seconds, especially for large networks like cloud providers. We show identity info immediately while prefixes load in the background.
What are IP prefixes in the context of ASN?
IP prefixes are blocks of IP addresses that an ASN announces to the internet via BGP. Each prefix is shown in CIDR notation (e.g., 8.8.8.0/24), which indicates the network address and size. We show the CIDR, range start, range end, and total address count for each prefix.
What's the difference between IPv4 and IPv6 prefixes?
IPv4 prefixes use 32-bit addresses (e.g., 8.8.8.0/24 = 256 addresses), while IPv6 prefixes use 128-bit addresses (e.g., 2001:4860::/32 = trillions of addresses). Most ASNs announce both types. Use the tabs to filter by IPv4, IPv6, or view all together.
What are Regional Internet Registries (RIRs)?
RIRs are organizations that manage IP address and ASN allocation in specific regions: ARIN (North America), RIPE NCC (Europe, Middle East), APNIC (Asia Pacific), AFRINIC (Africa), and LACNIC (Latin America). The registry shown indicates which RIR allocated the ASN.
Is this ASN Lookup tool free to use?
Yes, completely free with no usage limits and no account required. All data comes from public RDAP/whois sources and our local databases. We also provide a free REST API for programmatic access.