What is an ASN?
The internet is a network of networks. Each independently operated network, such as an ISP, a cloud provider, a university or a large company, is an autonomous system (AS) identified by a unique Autonomous System Number. Networks use the Border Gateway Protocol (BGP) to announce which IP prefixes they own, and every route on the internet is a path of AS numbers. Read our full guide to ASNs.
What you can do with an ASN lookup
- Identify who operates an IP address, for example to tell whether traffic comes from a residential ISP, a mobile carrier or a cloud data centre.
- List every prefix an organization announces, which is useful for firewall allowlists, threat intelligence and network planning.
- Check routing status: an AS that stops announcing prefixes may be having an outage.
- See its upstream providers and how well connected it is.
Understanding the results
- Holder: the organization registered for the AS number at its regional internet registry.
- Announced prefixes: IP blocks this AS currently originates in BGP, as seen by RIPE's global route collectors.
- Neighbours: "upstream" counts networks seen to the left of this AS in BGP paths (providers and peers); "downstream" counts networks to its right (customers).
Frequently asked questions
How do I find my own ASN?
Click "your IP" above, or see the ASN on the home page and What Is My ISP.
What is the difference between 16-bit and 32-bit ASNs?
Original AS numbers were 16-bit (up to 65,535). Since RFC 4893 (now RFC 6793), 32-bit ASNs allow over four billion networks. Ranges 64512–65534 and 4200000000–4294967294 are reserved for private use.