Back to glossary

Autonomous System

A collection of IP networks and routers under the control of a single entity that presents a common routing policy to the internet.

AbbreviationAS
Categorynetwork

Overview

An Autonomous System (AS) is a fundamental building block of the internet's global routing architecture. Each AS is assigned a unique Autonomous System Number (ASN) by IANA.

Role in Routing

  • Intra-AS Routing: Routing within an AS (using IGPs like OSPF or EIGRP).
  • Inter-AS Routing: Routing between different ASes (using BGP).

Types of ASes

  • Stub AS: Connected to only one other AS.
  • Multihomed AS: Connected to multiple ASes but does not allow transit traffic.
  • Transit AS: Provides connections to other ASes (e.g., ISPs).

Related Terms

Routing Protocol