An Autonomous System (AS) is a network or group of IP networks that are all under the control of a single entity or administration. ASes have clear borders and routing policies.
You can uniquely identify such AS by their autonomous system number assigned by the Internet Assigned Numbers Authority (IANA), an AS Number (ASN).
ASes use the Border Gateway Protocol (BGP) to exchange routing and reachability information with neighboring ASes. A direction connection between two ASes is called a BGP peering relationship.
Example AS: AS32934, Facebook.com Peers, as exchanged by the BGP can be seen below.
Sources
- Why the Internet Is Both Robust and Fragile, ByteByteGo NewsLetter