What Is an ASN?

An Autonomous System Number (ASN) is a unique identifier for an autonomous system (AS): a network or group of networks run under one routing policy that speaks BGP with other networks on the internet. ASNs let routers know which organization advertises which IP prefixes.

Table of Contents

  1. How do ASNs work?
  2. Why does this matter for click fraud and ad fraud?

How do ASNs work?

Large providers, hosting companies, enterprises, and universities obtain an ASN from a regional internet registry. They announce IP blocks to peers and upstreams using BGP. Each announcement is tied to an ASN so other networks can build a global routing picture.

Public ASNs appear in global routing. Private ASNs exist for special cases (for example single-provider setups) and are not meant for the public internet. When you look up an IP, its origin is often described as “AS12345 Example ISP,” which is that network’s ASN and name.

ASNs do not replace IP addresses. They group prefixes under an operator. Two servers in the same datacenter may share an ASN; a mobile user’s IP maps to a different ASN belonging to a carrier.

Why does this matter for click fraud and ad fraud?

Fraud detection uses ASN data as a reputation and context signal. Datacenter and bulletproof host ASNs behave differently from residential or mobile carrier ASNs. A burst of ad clicks from many IPs inside a small set of ASNs can indicate automation or purchased traffic.

ASN is one input next to device signals, velocity, and conversion quality. It helps answer whether traffic looks like everyday consumer ISP users or infrastructure rented for bots and proxies. That supports decisions aligned with how fraud is detected, how suspicious clicks are scored, and how click fraud investigations use network context alongside ad fraud patterns.

For more detail on internet numbering policy, see ARIN’s ASN guide.

Frequently Asked Questions

  • Is an ASN the same as an IP address?

    No. IPs identify hosts or endpoints on a network. An ASN identifies the organization that operates BGP routing for a collection of prefixes that contain those IPs.

  • Can attackers change their ASN?

    They choose where to host or buy transit. Traffic still exits through some ASN. Sophisticated fraud may mix residential proxies and mobile IPs, which shifts ASN patterns rather than removing them.

  • Does every website need its own ASN?

    No. Most sites run on hosting or cloud providers that use the provider’s ASN. You still benefit from ASN-aware filtering on the buyer side of ads and on fraud products that analyze click sources.

Abisola

Abisola

Meet Abisola! As the content manager at ClickPatrol, she’s the go-to expert on all things fake traffic. From bot clicks to ad fraud, Abisola knows how to spot, stop, and educate others about the sneaky tactics that inflate numbers but don’t bring real results.