Route Tables and Routing

Route tables are the traffic directors of your VPC. Every packet that leaves a subnet is evaluated against the route table associated with that subnet, and the most specific matching route determines where the packet goes. Without properly configured route tables, your subnets cannot communicate — with each other, with the internet, or with on-premises networks.

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What Is a Route Table?

A route table is a set of rules (called routes) that determine where network traffic is directed. Each route has two fields:

Field	Description
Destination	The CIDR block the traffic is heading to (e.g. 10.0.0.0/16, 0.0.0.0/0)
Target	Where to send it (e.g. local, igw-xxxx, nat-xxxx, pcx-xxxx)

The Local Route

Every route table automatically contains a local route that enables communication within the VPC:

Destination	Target
10.0.0.0/16	local

This route cannot be removed. It ensures that instances in any subnet of the VPC can talk to instances in any other subnet (subject to security group and NACL rules).

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Main Route Table vs Custom Route Tables

Main Route Table