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Route Tables — Directing Network Traffic in Cloud Environments

A Route Table is a collection of routing rules that determines where network traffic should be forwarded. Every packet that enters or leaves a subnet is evaluated against a route table to determine its next destination. Route tables are fundamental to cloud networking in AWS, Microsoft Azure, and Google Cloud, enabling communication between subnets, the Internet, VPNs, hybrid networks, and cloud services. Every Cloud Architect, DevOps Engineer, Platform Engineer, Site Reliability Engineer (SRE), Network Engineer, and Security Engineer should understand how route tables work.

Learning Path

Networking Mastery → Module 10: Cloud Networking → Lesson 5

Difficulty: Intermediate

Reading Time: 170 Minutes

Course Progress

Course: Networking Mastery

Module: Cloud Networking

Lesson: 5 of 10

What You'll Learn

After completing this lesson, you'll be able to:

  • Understand route tables
  • Learn how routing decisions are made
  • Configure default routes
  • Route traffic to the Internet
  • Connect private subnets using Network Address Translation (NAT)
  • Understand cloud routing across AWS, Azure, and GCP
  • Design production-ready routing architectures

Prerequisites

Complete:

Why Are Route Tables Important?

Imagine a web server wants to reach:

www.example.com

The server asks:

Where

Should

I Send

This Packet?

The answer comes from:

Route Table

Without routing:

Packets

Cannot

Reach

Their Destination

What is a Route Table?

A Route Table is:

A

List

Of

Routing Rules

Each rule tells the network:

Destination Network

↓

Next Hop

How Routing Works

Packet arrives:

Packet

↓

Route Table

↓

Matching Route

↓

Next Hop

↓

Destination

Every packet follows this process.

Route Entry Structure

Every route contains:

Field Description
Destination Target network
Next Hop Where packets should go
Priority Determines which route is selected (platform dependent)

Example:

Destination Next Hop
10.0.0.0/16 Local
0.0.0.0/0 Internet Gateway

Local Route

Every cloud network automatically creates a local route.

Example:

10.0.0.0/16

↓

Local

This enables communication between resources inside the same virtual network.

Default Route

The default route matches:

0.0.0.0/0

Meaning:

Any

Unknown

Destination

Example:

0.0.0.0/0

↓

Internet Gateway

Public Subnet Routing

Public Subnet

↓

Route Table

↓

Internet Gateway

↓

Internet

Resources with public IP addresses can communicate with the Internet.

Private Subnet Routing

Private resources usually cannot reach the Internet directly.

Instead:

Private Subnet

↓

Route Table

↓

NAT Gateway

↓

Internet

Inbound Internet traffic remains blocked.

Multiple Route Tables

Large environments often use different route tables.

Example:

Public Route Table

Private Route Table

Database Route Table

Each subnet can be associated with the appropriate routing policy.

Longest Prefix Match

When multiple routes match a destination, the most specific route is selected.

Example:

Destination Next Hop
10.0.0.0/16 Local
10.0.1.0/24 Firewall
0.0.0.0/0 Internet Gateway

Traffic to:

10.0.1.25

uses:

10.0.1.0/24

because it is the most specific match.

AWS Route Tables

AWS Route Tables can forward traffic to:

  • Local Network
  • Internet Gateway
  • NAT Gateway
  • VPC Peering
  • Transit Gateway
  • Virtual Private Gateway
  • Network Interfaces

Example:

Destination Target
10.0.0.0/16 Local
0.0.0.0/0 Internet Gateway

Azure Route Tables

Azure supports:

  • System Routes
  • User-Defined Routes (UDRs)

Traffic can be directed to:

  • Internet
  • Virtual Appliance
  • VPN Gateway
  • Virtual Network
  • Azure Firewall

Google Cloud Routes

Google Cloud automatically creates:

  • Local Routes
  • Default Internet Route

Custom routes can forward traffic to:

  • Cloud VPN
  • Cloud Router
  • Internal Load Balancers
  • Network Appliances

Hybrid Routing

Example:

Cloud

↓

VPN Gateway

↓

On-Premises

Route Table:

192.168.0.0/16

↓

VPN Gateway

Traffic for the on-premises network follows the VPN tunnel.

Multi-Region Routing

Example:

Region A

↓

Route

↓

VPN

↓

Region B

or

Region A

↓

Cloud Backbone

↓

Region B

depending on the cloud provider and architecture.

Enterprise Architecture

Internet

↓

Internet Gateway

↓

Public Subnet

↓

Application

↓

Database

↓

VPN Gateway

↓

On-Premises

Each network segment uses route tables to determine packet forwarding.

Kubernetes Perspective

In Kubernetes:

  • Nodes maintain routing information.
  • Container Network Interface (CNI) plugins configure Pod routes.
  • Services rely on routing for communication.
  • Cloud route tables integrate with cluster networking.

Understanding route tables helps troubleshoot Pod connectivity and hybrid networking.

Cloud Perspective

Route tables determine traffic flow between:

  • Subnets
  • Virtual Networks
  • Internet
  • VPNs
  • Cloud Services
  • Load Balancers
  • Hybrid Networks

Proper routing is essential for scalable cloud architectures.

CLI Examples

AWS

List route tables.

aws ec2 describe-route-tables

Azure

List route tables.

az network route-table list

Google Cloud

List routes.

gcloud compute routes list

Common Route Destinations

Destination Next Hop
Local Network Local
Internet Internet Gateway
Private Internet Access NAT Gateway
VPN Network VPN Gateway
Another VPC/VNet Peering
Shared Services Transit Gateway / Hub

Hands-on Lab

Task 1

List AWS Route Tables.

aws ec2 describe-route-tables

Task 2

List Azure Route Tables.

az network route-table list

Task 3

List Google Cloud Routes.

gcloud compute routes list

Task 4

Design:

  • Public Route Table
  • Private Route Table

for a three-tier application.

Task 5

Add a default route to:

Internet Gateway

Task 6

Add a private subnet route to:

NAT Gateway

Task 7

Design routing for a hybrid environment connecting:

  • AWS
  • Azure
  • Google Cloud
  • On-Premises

Task 8

Draw a production routing architecture including:

  • Public Subnets
  • Private Subnets
  • Internet Gateway
  • NAT Gateway
  • VPN Gateway
  • Route Tables

Explain how traffic is routed from:

  • Internet User
  • Web Server
  • Application Server
  • Database

Production Troubleshooting

Problem:

EC2

Cannot

Reach

Internet

Check:

  • Route Table Association
  • Default Route
  • Internet Gateway
  • NAT Gateway
  • Security Rules
  • Network Access Control Lists (NACLs)
  • Firewall Rules

Workflow:

Instance

↓

Subnet

↓

Route Table

↓

Gateway

↓

Destination

Cloud Comparison

AWS Azure Google Cloud
Route Tables Route Tables + UDRs Global Routes
Internet Gateway Internet System Route Default Internet Gateway
NAT Gateway NAT Gateway Cloud NAT
Transit Gateway Virtual WAN Network Connectivity Center

Common Mistakes

❌ Forgetting the default route.

✅ Verify 0.0.0.0/0 configuration.

❌ Associating the wrong route table with a subnet.

✅ Validate subnet associations.

❌ Overlooking longest prefix matching.

✅ Review route specificity.

❌ Missing routes to hybrid networks.

✅ Configure VPN or interconnect routes.

❌ Assuming firewall issues when routing is incorrect.

✅ Verify routes before debugging security policies.

Best Practices

  • Use separate route tables for different subnet types.
  • Keep routing simple and predictable.
  • Use least-privilege network design.
  • Document every custom route.
  • Verify route propagation in hybrid environments.
  • Avoid overlapping CIDR ranges.
  • Test routing after every infrastructure change.
  • Monitor routing using cloud network monitoring tools.

Interview Questions

Beginner

  1. What is a Route Table?
  2. What is a default route?
  3. What is a local route?
  4. Why are route tables required?

Intermediate

  1. Explain longest prefix matching.
  2. Compare AWS, Azure, and GCP routing.
  3. How does a private subnet reach the Internet?
  4. What is a User-Defined Route (UDR)?

Architect Level

  1. Design routing for a multi-tier cloud application.
  2. Explain routing in a hybrid cloud architecture.
  3. How would you troubleshoot routing issues across multiple cloud providers?

Summary

In this lesson, you learned:

  • Route Tables
  • Routing Decisions
  • Default Routes
  • Local Routes
  • Longest Prefix Match
  • Internet Routing
  • Private Routing
  • Hybrid Routing
  • Cloud Routing Best Practices

Route tables are the decision-making engine of cloud networking. Every packet relies on routing rules to reach its destination. By combining local routes, default routes, NAT, VPNs, and cloud gateways, organisations can build secure, scalable, and highly available cloud network architectures across AWS, Azure, and Google Cloud.

Key Takeaways

  • A Route Table determines where network traffic is forwarded.
  • Every subnet is associated with a route table.
  • The default route (0.0.0.0/0) handles traffic destined for external networks.
  • Longest prefix matching selects the most specific route.
  • Public subnets route traffic through an Internet Gateway, while private subnets typically use a NAT Gateway.
  • Well-designed routing improves security, scalability, and reliability.

What's Next?

NAT Gateway

In the next lesson, you'll learn about NAT Gateway.

You'll explore:

  • What a NAT Gateway is
  • Source Network Address Translation (SNAT)
  • Public vs Private Internet Access
  • Outbound Connectivity
  • High Availability
  • Cloud NAT Services
  • Production Best Practices

By the end of the lesson, you'll understand how private cloud resources securely access the Internet without exposing themselves to inbound Internet traffic.