Explain about Route Tables?

Route Tables are one of the core networking components in AWS VPC architecture.

They determine how network traffic travels inside and outside the VPC.

Why Route Tables are Important

In cloud networking, resources communicate using IP routing.

Route Tables decide:

• Where traffic should go
• Whether internet access is allowed
• How subnets communicate
• How external networks are connected

High-Level Architecture

EC2 Instance
      |
Subnet
      |
Route Table
      |
Destination
    

Real-World Analogy

A Route Table works like Google Maps for network traffic.

It decides:

If destination = Internet
    go to Internet Gateway

If destination = Internal Network
    stay inside VPC
    

Main Components of Route Table

Basic Route Table Structure

Understanding the Routes

1. Local Route

10.0.0.0/16 → Local
    

This route allows communication within the VPC.

Example

EC2 Instance A
      |
VPC Internal Network
      |
EC2 Instance B
    

2. Internet Route

0.0.0.0/0 → Internet Gateway
    

This route sends all internet traffic to the Internet Gateway.

Types of Route Tables

Main Route Table

Every VPC automatically gets a Main Route Table.

Characteristics

• Default routing table
• Automatically associated with subnets
• Contains local route by default

Custom Route Table

Organizations create custom route tables for advanced routing control.

Use Cases

• Public subnet routing
• Private subnet routing
• NAT Gateway routing
• VPN connectivity

Public Route Table

Public Subnets use route tables connected to an Internet Gateway.

Architecture

Public EC2
     |
Public Route Table
     |
Internet Gateway
     |
Internet
    

Public Route Table Example

Private Route Table

Private Subnets typically use NAT Gateway for outbound internet access.

Architecture

Private EC2
      |
Private Route Table
      |
NAT Gateway
      |
Internet Gateway
      |
Internet
    

Private Route Table Example

Route Table Associations

Route Tables must be associated with subnets.

Architecture

Route Table
      |
Subnet Association
      |
Subnet
      |
EC2 Instances
    

How Routing Works Internally

Packet Generated
       |
Check Route Table
       |
Find Matching Destination
       |
Forward Traffic to Target
    

Longest Prefix Match Rule

AWS Route Tables use longest prefix matching.

Example

AWS chooses the most specific route.

Advanced Routing Targets

VPC Peering Routing

VPC A
   |
Route Table
   |
Peering Connection
   |
VPC B
    

Hybrid Cloud Routing

On-Premise Data Center
        |
VPN Gateway
        |
AWS Route Table
        |
VPC
    

Production Architecture Example

Internet
    |
Internet Gateway
    |
Public Route Table
    |
Public Subnet
    |
Load Balancer
    |
Private Route Table
    |
Application Subnet
    |
Database Subnet
    

Common Route Table Mistakes

• Missing internet route
• Incorrect NAT Gateway route
• Wrong subnet association
• Overlapping CIDR blocks

Security Best Practices

• Use separate route tables for public and private subnets
• Restrict unnecessary internet access
• Use private routing for databases
• Implement least privilege networking

Route Table vs Security Group

Real-World Banking Architecture

Internet
   |
Load Balancer
   |
Public Route Table
   |
Web Servers
   |
Private Route Table
   |
Application Servers
   |
Database Cluster
    

Interview Answer

Route Tables in AWS are collections of routing rules that determine where network traffic is directed inside a VPC.

Each route contains:

• Destination CIDR block
• Target resource

Route Tables are associated with subnets and control traffic flow to:

• Internet Gateway
• NAT Gateway
• VPN Gateway
• VPC Peering Connections

Public subnets typically route traffic to an Internet Gateway, while private subnets use NAT Gateway for outbound internet access.

Quick Summary Table

Useful Internal Links

• AWS Interview Questions
• Cloud Computing Interview Questions
• DevOps Interview Questions
• Docker Interview Questions
• Kubernetes Interview Questions

Final Conclusion

Route Tables are fundamental networking components in AWS VPC architecture.

They control how traffic flows between subnets, the internet, and external networks.

Understanding Route Tables is essential for designing secure, scalable, and production-ready AWS infrastructures.