What term describes a connected group of IP prefixes run by one or more network operators which has a SINGLE and CLEARLY DEFINED routing policy?

• A. Autonomous System
• B. Domain
• C. VLAN
• D. Subnet

Answer: (A)

An autonomous system is a connected group of IP prefixes that is operated under a single, clearly defined routing policy by one or more network operators. The essence is that traffic entering and leaving all the prefixes within that group is governed by one set of routing rules, typically implemented with BGP between different ASes. Inside the AS, you can have many subnets or networks, but they share that unified policy and routing behavior across the whole system. Each AS is identified by a unique Autonomous System Number (ASN), which helps routers on the internet know the boundary where the policies change.

This differs from a domain, which is a DNS naming space; a VLAN, which is a Layer 2 segmentation within a single local network; and a subnet, which is just a contiguous block of IP addresses within a single routing domain and doesn’t by itself describe an entire policy across multiple operators.