An Autonomous System (AS) is a collection of IP networks and routers under the control of one or more network operators that share a unified routing policy with the external internet. Each AS is assigned a unique Autonomous System Number (ASN), which serves as its public identifier for inter-domain routing. The Border Gateway Protocol (BGP) uses these ASNs to exchange routing information between different administrative domains, enabling the decentralized structure of the global internet.

From a cybersecurity standpoint, the secure configuration and operation of Autonomous Systems are critical for maintaining internet stability. Proper management of routing policies, accurate prefix advertisements, and secure peering relationships help prevent routing-based attacks such as BGP hijacking, where malicious actors redirect or intercept network traffic. Understanding AS architecture is essential for designing secure network infrastructures and ensuring reliable data delivery across the internet.