title: “VPC Internet Gateway” created: 2026-07-22 updated: 2026-07-22 type: knowledge tags:

aws
certification
networking
vpc

VPC Internet Gateway

What It Is

An Internet Gateway (IGW) is a VPC component that enables communication between resources in the VPC and the Internet. It serves as the gateway for all inbound and outbound Internet traffic.

Without an IGW, a VPC has absolutely no Internet connectivity. Understanding how the IGW interacts with route tables, public IPs, and subnets is essential for VPC design and troubleshooting connectivity issues.

Key Concepts

Characteristics

Horizontally scaled — handles any amount of traffic
Redundant and highly available — no single point of failure
Imposes no bandwidth constraints or availability risks
Supports both IPv4 and IPv6
One IGW per VPC (you cannot attach multiple)

Requirements for Internet Access

A resource in a VPC needs all three of these to reach the Internet:

An Internet Gateway attached to the VPC
A route in the subnet’s route table pointing 0.0.0.0/0 → IGW
A public IP address (or Elastic IP) assigned to the resource

If any of these is missing, outbound Internet access will fail.

What Makes a Subnet Public

A subnet is public if and only if its route table has a route to an Internet Gateway:

0.0.0.0/0 → igw-xxxxxxxx

How It Works

EC2 instance (public IP) → Route table → IGW → Internet
Internet → IGW → Route table → EC2 instance (public IP)

The IGW performs Network Address Translation (1:1 NAT) between the instance’s private IP and its public IP.

Gotchas

An IGW does not perform NAT for private IPs without a public/Elastic IP — those instances cannot reach the Internet through the IGW
Detaching an IGW immediately breaks all Internet connectivity for the VPC
You can have only one IGW per VPC
An IGW alone is not enough — the route table and public IP are also required

AWS Certification Notes