ASN Lookup
Look up registration details for any Autonomous System Number (ASN). Find organization, country, RIR, and network information using the RDAP protocol.
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.
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). ipv4.center 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.
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.