Look up any Autonomous System Number to find the network operator, announced IP prefixes, BGP peers, abuse contact and routing details.
Enter an ASN, IP address or domain name above to retrieve full network and routing details.
An Autonomous System Number (ASN) is a unique identifier assigned to a collection of IP networks operated by a single organisation with a unified routing policy. Every major network on the internet — ISPs, cloud providers, universities, banks, enterprises and content delivery networks — is identified by an ASN in the global BGP routing table. ASNs started as 16-bit numbers (AS1 to AS65535) but have extended to 32-bit, allowing over four billion unique values. They are assigned by five Regional Internet Registries: ARIN for North America, RIPE NCC for Europe and the Middle East, APNIC for Asia-Pacific, LACNIC for Latin America, and AFRINIC for Africa. To see the ASN associated with any IP address, use our IP Lookup tool which displays the AS number alongside ISP and geolocation details.
Enter any ASN (e.g. AS15169), IP address, or domain name and this tool returns the complete public network profile: organisation name and description, country of registration, network type classification (cloud, ISP, CDN, university, government, VPN, etc.), all announced IPv4 and IPv6 CIDR prefixes, an estimated total IPv4 address count derived from the prefix sizes, the list of BGP neighbours with upstream/downstream/peer relationship labels, and the registered abuse contact email. All data is fetched live from the RIPEstat Data API on every query — never cached. Combine with our WHOIS Lookup for domain registration details and our Reverse DNS tool to resolve any IP address back to its hostname.
An IP prefix is a contiguous block of IP addresses in CIDR (Classless Inter-Domain Routing) notation — for example 142.250.0.0/15 for IPv4 or 2001:4860::/32 for IPv6. When an ASN announces a prefix via BGP, it tells the rest of the internet that it is responsible for routing all traffic destined for that range. The prefix length determines block size: a /24 covers 256 addresses, a /16 covers 65,536, and a /8 covers over 16 million. Viewing the full prefix list for an ASN gives you a complete map of which IP ranges belong to that organisation — essential for firewall allowlisting, security research, network planning, and abuse investigation. Use our Subnet Calculator to break down any CIDR prefix into its host range, broadcast address, and usable IP count.
Enter the IP address or domain directly into the search box — no need to look up the ASN number first. For an IP address, the tool queries ip-api.com to identify the owning ASN, then fetches the full routing profile from RIPEstat. For a domain, it first resolves the domain to its primary IPv4 address via DNS (the same resolution our DNS Lookup tool performs), then follows the same path. You can also enter the AS number directly as AS15169, AS 15169, or just 15169.
BGP (Border Gateway Protocol) neighbours are autonomous systems that exchange routing information directly with the ASN you are looking up. The relationship type reflects the commercial and technical arrangement between the networks. An upstream neighbour is a transit provider that the ASN pays to carry its traffic to the rest of the internet. A downstream neighbour is a customer that pays the ASN for transit. A peer is a settlement-free arrangement where two networks of roughly equal size exchange each other's traffic at an internet exchange point without money changing hands. Understanding these relationships helps map how a network connects globally and can identify single points of failure or transit dependencies.
An ASN lookup focuses on routing infrastructure — which IP ranges an organisation announces via BGP, how many peers they have, and how their network connects globally. A WHOIS lookup focuses on registration records — who registered a domain name, when it expires, which nameservers it uses, and the registrar. For a complete investigation of any domain or IP, use all tools together: DNS Lookup to see live DNS records, WHOIS for ownership, ASN Lookup for the network routing profile, Reverse DNS to map IPs to hostnames, and our SSL Checker for certificate validity.
Like private IP address ranges (192.168.x.x, 10.x.x.x), certain ASN ranges are reserved for private use and should never appear in the public BGP routing table. In the 16-bit ASN space, AS64512 through AS65534 are private. In the 32-bit space, AS4200000000 through AS4294967294 are reserved for private use. ASN 0 and 65535 are also reserved. If you see one of these values in a lookup result, it indicates a private or test network configuration rather than a publicly registered autonomous system. ASN 23456 is a special placeholder used for backward compatibility when 32-bit ASNs appear in 16-bit BGP contexts.
Every registered ASN is required to maintain an abuse contact — typically an email address for reporting malicious activity originating from IPs within that network's announced prefixes. Security teams, hosting providers and ISPs use this contact to report spam campaigns, port scanning, DDoS traffic, phishing infrastructure, malware hosting and other network abuse. This tool displays the abuse contact from the RIPEstat registry so you can reach the right team immediately. To check what services are running on a suspicious IP before filing a report, use our Port Checker to test specific ports, and our Reverse DNS tool to identify the hostname.
In CIDR notation, the number after the slash indicates how many bits are fixed in the network address, with the remaining bits available for host addresses. A /24 covers 256 addresses. A /16 covers 65,536 addresses. A /8 covers 16,777,216 addresses — allocated only to very large networks. IPv6 prefixes work the same way but with 128-bit addresses; a typical end-site allocation is a /48, while a /32 is a large provider allocation. To break down any CIDR prefix into its exact host range and usable IP count, use our Subnet Calculator. To check whether a domain supports both IPv4 and IPv6, run a DNS Lookup and look for both A (IPv4) and AAAA (IPv6) records.
Yes — completely free with no sign-up required. You can search by AS number, IP address, or domain name with no limit on queries. All prefix and neighbour data is fetched live from the RIPEstat API on every lookup, and all announced prefixes can be copied to the clipboard in one click for use in firewall rules or network analysis tools. For a complete network investigation, combine it with our IP Lookup, DNS Lookup, WHOIS Lookup, Reverse DNS, and Port Checker tools.