In this blog, I’ll:

• Explain core AWS networking concepts in simple terms

• Walk through a real project I built using Test & Prod VPCs

• Show how EC2s communicate within a VPC and across VPCs

🌐 What is a VPC?

A VPC (Virtual Private Cloud) is your own private network in AWS where you can launch resources like EC2, RDS, ALB, etc.

👉 You control:

• IP address range (CIDR)

• Subnets

• Routing

• Internet access

Example:

VPC CIDR: 10.0.0.0/16

🧩 What is a Subnet?

A subnet is a smaller network inside a VPC.

🔓 Public Subnet

• Connected to Internet Gateway

• Can have public IPs

• Used for: Bastion, Web servers, NAT Gateway

🔒 Private Subnet

• No direct internet access

• Uses NAT Gateway for outbound traffic

• Used for: App servers, Databases

📘 What is a Route Table?

A route table decides where network traffic goes.

Common Routes

Each subnet must be associated with a route table.

🌍 Internet Gateway (IGW)

An Internet Gateway allows resources in public subnet to:

• Receive traffic from the internet

• Send traffic to the internet

👉 IGW is attached to the VPC, not directly to EC2.

🔁 NAT Gateway

A NAT Gateway allows private subnet resources to:

• Access the internet (outbound only)

• Stay protected from inbound internet traffic

📌 NAT Gateway:

• Lives in public subnet

• Has an Elastic IP

🔢 What is CIDR?

CIDR defines the IP address range.

Examples:

Example:

VPC: 10.0.0.0/16
Public Subnet: 10.0.1.0/24
Private Subnet: 10.0.2.0/24

🔗 What is VPC Peering?

VPC Peering connects two VPCs privately so they can communicate using private IPs.

✔️ Traffic stays inside AWS
✔️ No public internet
❌ CIDRs must NOT overlap
❌ No transitive routing

🛠️ My Hands-on AWS Networking Project

🧪 Project Architecture Overview

I created two separate VPCs:

• Test VPC

• Prod VPC

Each VPC has:

• 1 Public Subnet

• 1 Private Subnet

• Internet Gateway

• NAT Gateway

• EC2 instances

  

  

📌 Step 1: Create VPCs

📌 Step 2: Create Subnets (4 Total)

Test VPC

• Public Subnet → 10.0.1.0/24

• Private Subnet → 10.0.2.0/24

Prod VPC

• Public Subnet → 192.0.1.0/24

• Private Subnet → 192.0.2.0/24

📌 Step 3: Create & Attach Internet Gateways

• 1 IGW for Test VPC

• 1 IGW for Prod VPC

• Attached each IGW to its respective VPC

📌 Step 4: Create NAT Gateways

• NAT Gateway in each public subnet

• Elastic IP attached

• Used by private subnets for internet access

📌 Step 5: Create Route Tables (4 Total)

Public Route Tables

0.0.0.0/0 → Internet Gateway

Private Route Tables

0.0.0.0/0 → NAT Gateway

Each route table was explicitly associated with its subnet.

📌 Step 6: Launch EC2 Instances (4 Total)

🌍 Internet Connectivity Validation

✔️ Public EC2 → Internet via IGW
✔️ Private EC2 → Internet via NAT Gateway

All EC2s successfully accessed the internet.

🔁 Intra-VPC Communication (ICMP Ping)

• Public EC2 ↔ Private EC2 (same VPC)

• Ping works using private IP

• Enabled ICMP in security groups

📌 Security Groups are stateful, so return traffic is allowed automatically.

🔗 Inter-VPC Communication (Test ↔ Prod)

What I Did:

1. Created VPC Peering between Test & Prod VPC

2. Updated route tables:

Test VPC → 192.0.0.0/16 → Peering Connection
Prod VPC → 10.0.0.0/16 → Peering Connection

3. Allowed ICMP in security groups

   

Result:

✔️ EC2 in Test VPC can ping EC2 in Prod VPC
✔️ Communication happens using private IPs

✅ Key Learnings

• Routing controls traffic flow, not subnets alone

• NAT Gateway is only for outbound internet

• Security Groups control ICMP behavior

• VPC Peering requires route updates on both sides

• CIDR planning is critical for future scaling

🎯 Final Thoughts

This project helped me deeply understand AWS networking fundamentals by implementing them practically rather than just reading theory.

If you’re learning AWS, I highly recommend building something like this—it clears 90% of networking confusion.