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Autonomous System Number (ASN)

A globally unique identifier assigned to an autonomous network routing group on the BGP protocol, used by security systems to classify IP legitimacy into residential, datacenter, or mobile tiers.

An Autonomous System Number (ASN) is a globally unique number assigned by internet registries that identifies an Autonomous System (AS)—a massive collection of connected IP routing prefixes controlled by one or more network operators that present a single, clearly defined routing policy to the global internet.

ASNs are the foundational building blocks of the Border Gateway Protocol (BGP), the protocol that routes all data across the global internet.

In modern cybersecurity, bot mitigation, and proxy architecture, the ASN is the single most important metric used to determine whether an IP address belongs to a human or a bot.

Who Assigns ASNs and How They Are Structured (link to this section)

ASNs are managed globally by the Internet Assigned Numbers Authority (IANA) and allocated through five Regional Internet Registries (RIRs):

  • ARIN: North America
  • RIPE NCC: Europe, Middle East, Central Asia
  • APNIC: Asia-Pacific
  • LACNIC: Latin America and Caribbean
  • AFRINIC: Africa

Examples of well-known ASNs:

  • AS7922: Comcast Cable Communications (Residential Consumer ISP)
  • AS7018: AT&T Services, Inc. (Consumer & Enterprise Telecom)
  • AS16509: Amazon.com, Inc. / AWS (Cloud Hosting Datacenter)
  • AS14061: DigitalOcean, LLC (Cloud Hosting Datacenter)
  • AS22394: Cellco Partnership / Verizon Wireless (Mobile Cellular Carrier)

How Anti-Bot Systems Use ASN Classification (link to this section)

When a web scraper or automated browser sends a request to a website protected by Cloudflare, DataDome, or Akamai, the firewall performs a sub-millisecond lookup against threat databases (such as MaxMind GeoIP2, IPinfo, and Spur).

The firewall categorizes the incoming ASN into specific usage tiers:

1. Consumer ISP / Residential ASNs (High Trust) (link to this section)

Assigned to home broadband providers (Comcast, Charter, Virgin Media, Deutsche Telekom). Because millions of real consumers connect from these ASNs, anti-bot firewalls assign high trust scores. Banning these ASNs would alienate real customers.

2. Hosting / Data Center ASNs (Low Trust / High Bot Risk) (link to this section)

Assigned to server facilities (AWS, OVH, Hetzner, DigitalOcean). Legitimate humans do not browse the web from an Amazon EC2 server. Consequently, anti-bot engines automatically enforce strict rate limits or issue CAPTCHAs to requests arriving from hosting ASNs.

3. Mobile / Cellular ASNs (Exceptional Trust) (link to this section)

Assigned to wireless carriers (Verizon Wireless, T-Mobile, EE). Due to Carrier-Grade NAT (CGNAT), hundreds of real mobile phones share each public IP, granting mobile ASNs the most forgiving rate limits on the internet.

Subnets and Contiguous IP Ranges within an ASN (link to this section)

Within each Autonomous System, IP addresses are grouped into routing blocks called subnets:

  • /24 Subnet: A block of 256 contiguous IP addresses (e.g., 192.0.2.0 through 192.0.2.255).
  • /16 Subnet: A block of 65,536 contiguous IP addresses.

When scrapers use cheap datacenter proxies, anti-bot systems frequently execute subnet-level banning: if 10 IP addresses within a /24 datacenter block exhibit scraping patterns, the firewall blocks the entire 256-IP range, neutralizing all proxies in that block.

How Scrapers Leverage ASN Targeting (link to this section)

Advanced proxy providers allow scrapers to target specific ASNs directly:

http://user-asn-7922:password@gate.proxy.com:8000

By routing scraping traffic exclusively through premium consumer broadband ASNs (like Comcast or AT&T), scrapers significantly reduce CAPTCHA challenge rates.

In practice

  • Cloudflare automatically allowing requests from ASN 7922 (Comcast) while challenging any request from ASN 14061 (DigitalOcean) with a Turnstile CAPTCHA.
  • A scraping engineer filtering their residential proxy pool to target high-reputation European telecom ASNs (like Deutsche Telekom or Orange) to boost scraping success rates.
  • An e-commerce fraud prevention engine flagging an order as high-risk because the buyer's IP belongs to a hosting ASN rather than a consumer ISP.
  • Inspecting an unfamiliar proxy IP on ProxyRaw's IP lookup tool to determine its ASN, organization name, and network category.

Common use cases

Anti-bot threat evaluation and WAF rule configurationProxy pool quality verification and ASN filteringNetwork routing and BGP traffic engineeringE-commerce fraud prevention and risk scoringCybersecurity threat intelligence and reconnaissance

Frequently asked

Websites query IP intelligence databases (like MaxMind, IPinfo, and Spur) that continuously ingest public BGP routing tables from Regional Internet Registries (RIRs) to map every public IP address to its registered ASN.

Generally no, unless using an ISP proxy (static residential). ISP proxies use commercial agreements where consumer ISPs formally announce datacenter IP ranges, granting the IP a legitimate consumer ASN.

An IP address identifies a specific single device on the internet. An ASN identifies an entire network of thousands or millions of IP addresses managed by a single organization that routes traffic using BGP.

Because bots frequently rotate through adjacent IPs within the same hosting subnet. Banning the entire /24 range (256 IPs) prevents the bot operator from simply hopping to the next consecutive IP in their server block.

Related terms

Datacenter ProxyResidential ProxyISP ProxyMobile ProxyReverse Proxy