Explained
An ASN (Autonomous System Number) is a globally unique 16- or 32-bit number assigned to each network operator by IANA. Every ISP, hosting provider, content network, and large enterprise has at least one ASN. The ASN is how networks identify themselves to each other in BGP, the routing protocol that holds the public internet together.
When an IP address is routed across the internet, the BGP path traces back to a specific ASN. Anyone can look up which ASN owns any IP using public databases (RIPE, ARIN, Hurricane Electric, MaxMind). For an IP like 73.158.97.42, the lookup returns 'AS7922 (Comcast)'. For 13.107.42.14, you get 'AS8068 (Microsoft)'. The ASN tells you whether you're talking to a consumer ISP, a cloud hosting provider, a CDN, or a corporate network.
For anti-bot systems, ASN is the single most reliable signal for distinguishing residential traffic from datacenter traffic. Cloudflare, Akamai, PerimeterX, and others maintain comprehensive lists of datacenter ASNs and instantly flag traffic from them. That's why datacenter proxies fail on protected sites — the ASN gives them away. Residential proxies route through consumer ISP ASNs (Comcast, AT&T, BT, Vodafone, etc.), which carry the trust profile of real consumer traffic.
How It Works
Each ASN announces (via BGP) a set of IP prefixes it controls. When a packet arrives at a website, the server can look up the source IP against a BGP table or third-party ASN database to find the originating ASN. The ASN's category (consumer ISP, hosting provider, mobile carrier, cloud) is then used as a feature in risk scoring.
For proxy services, ASN is also a targeting parameter. A user can request 'a residential IP on AS7922' (Comcast) and the gateway filters the residential pool to IPs whose ASN matches. This produces ISP-segment-specific traffic for use cases like ad verification on a specific carrier or per-ISP feature testing.