Sign up free

ASN Lookup by AS Number, IP Address or Domain

Look up an autonomous system by number, IP or domain, and list the IP ranges it announces.

About ASN Lookup

An ASN lookup tells you which network an address really belongs to and what else that network runs. Type an AS number, such as AS13335 or just 13335, or enter an IP address or a domain to find the AS that announces it. It helps when a wave of scraper traffic comes from one hosting company and you want to block its ranges, when a partner asks you to let their network through your firewall, or when you simply want to know who runs AS4134.

Registration details come over RDAP, with the AS name, handle, organization, country, registry and the registered and updated dates. The IPv4 and IPv6 prefixes the AS announces come from RIPEstat, with a total for each and a table of up to 500 prefixes that you can copy or save as CSV. Each prefix links to IP WHOIS Lookup for its own record. Big carriers announce thousands of prefixes, so the table stops at 500 while the totals still count them all. Nothing is stored, and the lookup doesn't use your daily tasks.

How to use ASN Lookup

  1. 1
    Enter an AS number, IP or domain

    Type AS13335, 13335, an IP address or a domain name.

  2. 2
    Click Look up

    Large networks take a little longer while their prefix list loads.

  3. 3
    Read the registration

    See the AS name, organization, country, registry and dates.

  4. 4
    Export the prefixes

    Copy the Announced prefixes table or save it as CSV, or click a prefix to look it up.

Why use Cubfile for this

  • Number, IP or domain

    Start from an AS number with or without AS, or from any public IP or domain.

  • Announced prefixes

    IPv4 and IPv6 ranges from RIPEstat, with totals and up to 500 listed.

  • Copy or CSV

    Take the prefix list into a firewall rule, a spreadsheet or a report.

  • One click to IP WHOIS

    Every prefix opens its own registration record.

FAQ

ASN Lookup: questions and answers

What is an ASN (autonomous system number)?
An autonomous system number identifies a network that manages its own routing on the internet, such as an internet provider, a cloud company or a large organization. Each AS announces the IP ranges it's responsible for.
How do I find the ASN of an IP address?
Enter the IP address, or a domain, instead of a number. The tool finds the AS that announces it and shows that AS's details and prefixes. Your own network's AS number is shown on What Is My IP.
How can I get all the IP ranges of a company?
Look up its AS number and save the Announced prefixes table as CSV. Some companies use several AS numbers, and servers they rent from a cloud provider appear under the provider's AS instead. To see how many addresses a prefix covers, enter it in the IP Subnet Calculator.
Why are only 500 prefixes listed?
Very large networks announce thousands. The table shows the first 500, while the IPv4 and IPv6 totals count every one.
Is this ASN lookup tool free to use?
Yes, with no sign-up, and it doesn't use your daily tasks. Each visitor has an hourly lookup allowance, higher for members and VIP, and results aren't stored.
Share ASN Lookup with a friendIt runs in any browser, and they can try it without signing up.

Related tools

IP Ping TestMeasure how fast our server can connect to a host, several times in a row.
IP What Is My IPSee the public IP address websites see, plus your browser and system details.
IP IP WHOIS LookupSee which organization owns an IP address, its network range and ASN.
IP Open Port CheckerCheck whether common ports on your server are open to the internet.
IP IP Subnet CalculatorNetwork, host range and mask for IPv4 and IPv6, plus the broadcast address for IPv4.
IP User Agent ParserTurn a user agent string into browser, engine, system and device.
IP IP Address ConverterConvert IP addresses between dotted, decimal, hex and binary, and expand IPv6.
v6IP IPv6 Support CheckerCheck whether a website has IPv6 addresses and answers over IPv6.