Apr 30, 2025
The Internet is not a single network. It is a collection of independently operated networks connected through a common system of routing protocols and agreements.
Your home network connects to an Internet service provider. That provider connects to other networks, which may connect to cloud platforms, content delivery networks, universities, and enterprises around the world.
But how do these independently operated networks decide where traffic should go?
One of the most important pieces of the answer is Border Gateway Protocol (BGP).
BGP is the routing protocol used to exchange reachability information between autonomous systems. It plays a central role in determining how traffic moves across the global Internet.
An autonomous system (AS) is a collection of IP networks and routers managed under a common routing policy.
For example, an Internet service provider may operate a nationwide network. A cloud provider may operate data centers in several regions. A large enterprise may connect multiple offices and external networks.
Each of these organizations can operate an autonomous system.
Autonomous systems are identified by autonomous system numbers (ASNs). Public ASNs are allocated through the Internet number registry system.
A simplified network might look like this:
AS 65001
Network A
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AS 65002
Network B
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AS 65003
Network C
In this example, each AS represents an independently administered routing domain.
The numbers are illustrative private-use AS
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