ASN Lookup
Look up registration details for any Autonomous System Number (ASN). Find organization, country, RIR, and network information using the RDAP protocol. A free tool by IPv4Center.
What Is an ASN Lookup?
An ASN (Autonomous System Number) lookup retrieves information about a specific autonomous system on the internet. An AS is a collection of IP networks under the control of a single organization that presents a common routing policy to the internet. Each AS is identified by a unique ASN assigned by a Regional Internet Registry (RIR). ASN lookups are essential for network engineers, security researchers, and anyone involved in BGP routing, peering agreements, or IPv4 transactions. Our tool uses RDAP (Registration Data Access Protocol) to query authoritative RIR databases for the most accurate and up-to-date information.
How Does ASN Lookup Work?
When you enter an ASN, our tool queries the RDAP servers maintained by the relevant Regional Internet Registry (RIPE NCC, ARIN, APNIC, LACNIC, or AFRINIC). The RDAP response includes the AS name, managing organization, registration country, allocation status, and associated events. Unlike legacy WHOIS, RDAP provides structured JSON data with standardized fields, making it easier to parse and integrate into automated workflows.
What Is an Autonomous System Number (ASN)?
An Autonomous System Number (ASN) is a globally unique identifier assigned to a network or group of networks that operates under a single routing policy and is managed by one administrative entity. ASNs are the fundamental building blocks of inter-domain routing on the internet — they enable BGP (Border Gateway Protocol, RFC 4271) routers to identify and exchange routing information between independently operated networks.
ASNs exist in two formats: 2-byte (16-bit) ASNs ranging from 1 to 65534, and 4-byte (32-bit) ASNs ranging from 1 to 4294967294 as defined in RFC 6793. The 2-byte pool was exhausted by most RIRs between 2013-2019, making 4-byte ASNs the standard for new allocations. All modern BGP implementations support 4-byte ASNs, though they are sometimes represented in "asdot" notation (e.g., 1.5) for backward compatibility.
Every network that participates in BGP routing requires an ASN to announce its IP prefixes to the global routing table. As of 2026, there are approximately 80,000 unique ASNs visible in the Default-Free Zone (DFZ), though over 120,000 ASNs have been allocated. The difference represents private networks, reserved ranges (64512-65534 for 16-bit, 4200000000-4294967294 for 32-bit), and allocated but not yet deployed systems.
ASN Allocation by Regional Internet Registry
ASN allocation follows the same hierarchical model as IP addresses: IANA delegates blocks to the five Regional Internet Registries, which then assign individual ASNs to member organizations. RIPE NCC (serving Europe, Middle East, and Central Asia) manages the largest active ASN population with over 35,000 assigned ASNs, followed by ARIN (North America) with approximately 28,000.
APNIC (Asia Pacific) has allocated roughly 18,000 ASNs, while LACNIC (Latin America and Caribbean) manages approximately 10,000 and AFRINIC (Africa) around 4,000. Each RIR maintains its own allocation policies — RIPE NCC requires a sponsoring LIR for non-members, ARIN requires demonstrated multihoming need, and APNIC has a simplified one-click ASN request process for existing members.
Current 2-byte ASN allocation ranges by RIR include: ARIN 1-1791 and various blocks, RIPE NCC 1877-2047 and 12654-13311 among others, APNIC 4608-4865 and 7467-7722, LACNIC 27648-28671 and 52224-53247, and AFRINIC 36864-37887 and 327680-328703. New allocations since 2019 are exclusively from the 4-byte pool, with each RIR drawing from its designated 4-byte ranges.
Frequently Asked Questions
An ASN is a unique identifier assigned to an autonomous system (AS) — a network or group of networks under a single administrative domain. ASNs are used in BGP (Border Gateway Protocol) routing to identify and exchange routing information between networks on the internet. ASNs can be 16-bit (0–65535) or 32-bit (0–4294967295).
ASNs are assigned by Regional Internet Registries (RIRs). You need to be a member of or have a Sponsoring LIR with the relevant RIR (RIPE NCC, ARIN, APNIC, LACNIC, or AFRINIC). IPv4Center.com offers ASN registration services that handle the entire application process for you.
A 16-bit ASN ranges from 1 to 65534, while a 32-bit ASN ranges from 1 to 4294967294. 32-bit ASNs were introduced because the 16-bit pool was running out. Both types work identically in modern BGP implementations, but some legacy systems may not support 32-bit ASNs.
When buying or selling IPv4 addresses, knowing the ASN associated with a network helps verify the organization behind the IP block, understand the routing setup, and assess the network's reputation. ASN data is a key part of due diligence in IPv4 transfer processes. Learn more about what is ASN.
The RIR (Regional Internet Registry) field indicates which registry manages the ASN. There are five RIRs: RIPE NCC (Europe, Middle East, Central Asia), ARIN (North America), APNIC (Asia Pacific), LACNIC (Latin America, Caribbean), and AFRINIC (Africa). The RIR determines the transfer policies that apply to the ASN and associated IP resources.
You can look up any publicly registered ASN. Simply enter the ASN with or without the "AS" prefix (e.g., "13335" or "AS13335"). Private ASNs in the reserved ranges (64512–65534 for 16-bit, 4200000000–4294967294 for 32-bit) may not return useful results.