Full definition
An ASN (Autonomous System Number) is the identifier for a specific internet service provider — Comcast is AS7922, Verizon is AS701, Google is AS15169. ASN targeting lets you request a proxy IP that belongs to a specific ASN, useful when you need to verify how a site behaves for users on a specific ISP, or test routing through a specific peering relationship.
Real use cases include CDN performance testing (how does my site load for users on Comcast vs. Verizon?), ad verification (do mobile carrier IPs see different ad inventory?), and bypassing IP-based anti-bot rules that key off ASN.
Only enterprise-grade providers offer ASN targeting — Bright Data, Oxylabs, NetNut. Pool sizes are typically 50,000–70,000 distinct ASNs across global carriers.