BGP / ASN Reference

Overview

The BGP / ASN reference is a searchable list of well-known Autonomous System Numbers — Google's AS15169, Cloudflare's AS13335, Amazon's AS16509, plus tier-1 transit providers and large ISPs. Type a number or a name and the matching organisation, country, and approximate IP footprint appear instantly.

Network operators investigating a route leak, abuse desks tracking the origin of suspicious traffic, and engineers planning a peering arrangement all need to translate ASNs into human-readable owners. Long-tail keywords covered: look up ASN owner by number, find AS number for Cloudflare or Google, and identify which network announces an IP prefix.

How it works

The Border Gateway Protocol (BGP) is the routing protocol that stitches the public internet together. Each participant — an ISP, a hosting provider, a large enterprise — is assigned a globally unique Autonomous System Number by one of the regional registries (ARIN, RIPE, APNIC, LACNIC, AFRINIC). 16-bit ASNs run from 1 to 65535; 32-bit ASNs go up to 4,294,967,295. Numbers in the 64512–65534 range are reserved for private use, similar to RFC 1918 IP space.

When you trace a route or inspect a whois record, every public IP can be mapped back to an ASN. That ASN, in turn, identifies the organisation responsible for announcing the prefix into BGP. The mapping is published in the IRR and RDAP databases and is updated as prefixes are reallocated.

Examples

• AS15169 — Google LLC, announces most of 8.8.8.0/24 and Google Cloud egress.
• AS13335 — Cloudflare, Inc., announces 1.1.1.1 and the public resolver 1.0.0.1.
• AS16509 — Amazon.com, Inc., the bulk of AWS EC2 egress traffic.
• AS32934 — Facebook / Meta, including Instagram and WhatsApp media servers.

FAQ

What is the difference between a 16-bit and 32-bit ASN?

16-bit ASNs are the original IANA allocation and are running out. 32-bit ASNs were introduced in RFC 6793 and now make up the majority of new assignments. Modern BGP routers handle both transparently.

Why does one company own multiple ASNs?

Large operators separate ASNs by region, business unit, or function (transit vs content). Google, for example, holds AS15169 for production plus several others for peering and corporate networks.

How do I find the ASN for an arbitrary IP?

Use an RDAP lookup or a whois query against the bulk-whois servers; the response includes the origin ASN announcing that prefix.

Are private ASNs routable on the public internet?

No. ASNs in 64512–65534 and 4200000000–4294967294 are reserved for internal use and must be stripped before traffic exits to a public peer.

Try BGP / ASN Reference