Say the route aloud
Traffic for this destination goes to this target. I find that sentence useful for reading a route. Start with one request between application components and identify its destination before adding gateways or more routes.
Confirm the source subnet association
A correct route in the wrong table will not help the intended subnet. Check whether the association is explicit or uses the main table. Keep names and notes clear so the network remains understandable as more subnets are added.
Trace the reply
Sending a request out is only half of the connection. Check the return route and relevant access rules. When several routes could match, use the documented selection behaviour rather than guessing from display order or repeatedly adding entries.
Try it yourself
Write three destination-and-target statements, identify the source subnet’s table and trace the reply for each connection.
A common question
Is a route table a firewall?
No. Routes choose paths. Security groups, network ACLs and other controls govern permitted traffic in their own scopes.
References & video notes
Use the video to follow the topic with me. Console screens and older offers can change, so check the current AWS documentation before performing a lab.
Keep learning
- Public and private IP addresses in AWS
- EC2 security groups: allow the right connections
- Elastic IP addresses: when a stable public address helps