01 What is an Autonomous System (AS)?
An Explanation of the Structure of the Internet from the Perspective of an AS

How is the internet that we use every day constructed?
The internet can be described as a "network of networks," meaning it is made up of interconnected computer networks scattered around the world.

In this complex system, the unit for a network managed by a single organization is an AS (Autonomous System). In this article, we explain ASes, a fundamental structure of the internet, in a way that is easy for beginners to understand.

What is an AS (Autonomous System)?

An AS (Autonomous System) is a unit that makes up the internet. Enterprises and ISPs (Internet Service Providers)^*1 manage networks based on their routing policies, and these networks function as an AS. Each AS is assigned an AS Number, making it possible to differentiate it from other ASes.

*1 ISP (Internet Service Provider): A company that provides internet connections.

AS and Routing

Routing is the process of appropriately forwarding data, called packets, sent by computers to their destinations. In the world of the internet, routing is equivalent to navigation. Routing protocols^*2 play a crucial role in this routing. There are two types of routing protocols:

• EGP: For inter-AS routing
• IGP: For intra-AS routing

In other words, the scope controlled by IGP can also be considered an AS.

*2 Routing Protocol: A set of rules and agreements for determining the optimal path for data packets on a communication network.

The Role of AS Numbers

The BGP (Border Gateway Protocol), a protocol that supports the foundation of the internet, uses AS numbers. BGP is a type of EGP that enables communication between routers belonging to different ASes. An AS number makes it possible to identify accurate communication paths and appropriately transfer data.

Inter-AS Connections and IXes

A physical connection is necessary for direct communication between ASes. However, if each AS were connected one-to-one, it would require numerous connection lines, leading to complicated management and increased costs.
One solution to this problem is the use of IXes (Internet Exchanges). IXes refer to physical platforms that enable different ASes to exchange data efficiently.

Using IXes makes it possible to communicate with many ASes while reducing the number of physical direct connections, significantly improving the efficiency and flexibility of network operations.

Conclusion

The internet is a network of networks made up of interconnected ASes. ASes exchange route information using protocols such as BGP, and IXes are utilized for efficient traffic exchange between ASes.
The internet is established through the collaboration of many organizations and businesses that manage these networks.