Why is a route table not being checked when going into the IGW?

Question

When I send a package to my ec2-instance, no route table is being checked:

Only when send back:

Why is no route table checked, when sent into the network?

Answer 1

Unless you attach an Ingress Route Table to the IGW (also sometimes called "Gateway" Route Table), there is no explicit route table controlling traffic from the IGW to your VPC.

What happens is that the IGW translates the Public IPs of incoming network packets into the corresponding Private IPs, as long as the Public IPs are being used within the associated VPC. The Private IPs follow the default/implicit local-routing rules.

This translation is showcased in the result of your network path analysis with the dual Inbound header and Outbound header on the IGW (Fields missing in subsequent headers have simply not been changed).