What is an ASN, and how to find yours

If you've ever looked at an IP lookup and seen something like AS13335 · Cloudflare, Inc., that AS13335 is an ASN — an Autonomous System Number. Here's what it actually means.

The short version

The internet isn't one network — it's tens of thousands of independent networks that agree to route traffic to each other. Each of those networks is an Autonomous System (AS), and each gets a globally unique AS number.

• Your ISP is an AS (e.g. Comcast, Vodafone).
• Big cloud and CDN providers are ASes (Cloudflare is AS13335, Google is AS15169).
• Universities, banks, and large companies often run their own AS.

So an ASN answers the question "which network does this IP belong to?" — one level up from the individual address.

How to find yours

curl ipconfig.io/asn          # AS13335
curl ipconfig.io/asn-org      # Cloudflare, Inc.

Or get both alongside everything else in the JSON record:

curl -s ipconfig.io/json | jq -r '"\(.asn) — \(.asn_org)"'
# AS13335 — Cloudflare, Inc.

Find the ASN for any address

Append ?ip= to look up someone else's network:

curl ipconfig.io/asn-org?ip=8.8.8.8    # Google LLC

Why would I care about my ASN?

• It tells you who really carries your traffic. On mobile or behind a VPN, the ASN often reveals the actual upstream provider, not the brand on the box.
• It's how networks are filtered. Abuse lists, geo rules, and bot defenses frequently act per-ASN, not per-IP — so the AS your traffic exits from affects how the rest of the internet treats you.
• It's the unit of routing. BGP, the protocol that glues the internet together, advertises routes between AS numbers. The ASN is the address of your network on that map.

How AS numbers are assigned

ASNs are handed out by the Regional Internet Registries (ARIN, RIPE, APNIC, LACNIC, AFRINIC) — the same bodies that allocate IP blocks. Originally 16-bit (0–65535), the space was extended to 32-bit to keep up with growth, so modern ASNs can run well into the millions.

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Look up your own network now with curl ipconfig.io/asn, or see the API reference for the full record.