Route Tables, Internet Gateway, and NAT Gateway

Learning Objectives

By the end of this section, you will be able to:

• Explain how Layer 3 networking works inside an AWS Virtual Private Cloud (VPC).
• Understand the relationship between VPCs, subnets, and route tables.
• Distinguish between an Internet Gateway (IGW) and a NAT Gateway.
• Explain why public and private subnets exist.
• Trace how packets move from an EC2 instance to the Internet and back.
• Apply Layer 3 concepts to real-world cloud infrastructure.

Why Cloud Networking Still Uses Layer 3

When you deploy an application to AWS, Azure, or Google Cloud, the networking principles you learned earlier do not disappear.

Cloud providers build virtual networks, but those networks still rely on Layer 3 concepts such as:

• IP addressing
• Routing
• Subnets
• Gateways
• Route tables
• NAT