Autonomous Systems (AS)
💡 The Core Idea
An Autonomous System (AS) is the fundamental unit of routing on the Internet. It is a group of routers and IP prefixes operated by a single administrative authority (like an ISP or University) that applies a unified routing policy.
🧠Context
- Identification: Each AS is identified by a unique ASN (Autonomous System Number).
- Routing Protocols:
- IGP (Interior Gateway Protocol): Used inside the AS for efficiency (e.g., OSPF, IS-IS).
- EGP (Exterior Gateway Protocol): Used between ASes for policy (e.g., BGP).