Route Table Demo

This lesson demonstrates AWS VPC route tables: how to inspect them, how subnets are associated, and how route evaluation works (including longest-prefix matching). It covers the basic concepts and common operations you’ll use when managing VPC routing.

​

1) Create a VPC (with IPv6 enabled)

Start by creating a demo VPC (for example, named vpcdemo) and enable IPv6 if you need dual-stack addressing.

​

2) Create subnets in the VPC

Create two subnets inside the VPC. For example:

• Subnet A: 10.0.1.0/24 (with corresponding IPv6 block if using IPv6)
• Subnet B: 10.0.2.0/24

Availability Zone selection does not affect routing behavior — routing is decided at the subnet level.

​

3) Inspect the main route table

When a VPC is created, AWS automatically creates a main (default) route table for that VPC. Any subnet without an explicit association uses this main route table implicitly. Open the main route table to view its default entries. You will typically see:

• The VPC-local IPv4 route (example: 10.0.0.0/16)
• The VPC-local IPv6 prefix (if IPv6 is enabled)

These “local” routes are always present and are used to route traffic between subnets in the same VPC.

​

4) Subnet associations and implicit behavior

If you view the subnet associations for the main route table, AWS will show any subnets that are implicitly associated. These subnets inherit all routes from the main route table until you explicitly associate them with a different route table. When an instance sends a packet, VPC routing looks up the route table associated with that subnet and selects a route using longest-prefix (most specific) match based on the destination IP. Example of prefix specificity:

• 10.0.1.0/24 is more specific than 10.0.0.0/16, so traffic destined for 10.0.1.5 will match the /24 route first.

​

5) Create a custom route table and associate subnets

To apply custom routing behavior to a particular subnet, create a new route table for the VPC (for example, my-route-table-01) and then associate a subnet with it. After creating the route table, it will have no subnet associations initially. Use Edit subnet associations to choose which subnets should use this route table. Example: associate subnet1 with my-route-table-01. From that point, instances in subnet1 use my-route-table-01 for routing decisions. You can create and share route tables across multiple subnets — a 1:1 relationship is not required.

​

6) Common route edits and targets

Key points:

• VPC local routes are created automatically and cannot be removed.
• To enable internet access from subnets, add these routes:
  • IPv4 default route: Destination 0.0.0.0/0 -> target Internet Gateway (igw-...)
  • IPv6 default route: Destination ::/0 -> target Internet Gateway (or other IPv6-capable target)
• Other common targets: NAT Gateway, Virtual Private Gateway (VGW), VPC peering connection, Transit Gateway (TGW), Network Interface (ENI), or an instance (via instance ID in very specific scenarios).

Use the VPC console or APIs to add/modify routes. Changes apply immediately to any subnet associated with that route table. Table: Common route targets and use cases

​

7) Important note

​

8) Cleanup (avoid charges)

When you finish the demo, delete the VPC to avoid ongoing charges. Deleting a VPC will also remove many associated resources (subnets, route tables created for that VPC, etc.). Always review the deletion confirmation to verify which resources will be removed.

​

9) Links and references

• VPC route tables — AWS Documentation
• Working with route tables — AWS Console guide
• For general VPC concepts: Amazon VPC User Guide

That covers the basics: inspecting route tables, understanding implicit and explicit subnet associations, creating custom route tables, and adding routes for common targets.