Routing decision in AWS route table

Question

In AWS, if could you look at above picture, I understand that if any instance in subnet's attached to route table, is trying to hit the IP address between (10.0.0.0-10.0.255.255) should go to local, it should not go the Internet. Let's assume I have public IP address for my instance in public subnet of VPC, it is trying to hit the public IP address of external domain which has the ip address 10.0.0.5/32.

At that scenario, how routing happens, either to local or Internet?

Answer 1

Firstly the range of 10.0.0.0/8 is a reserved range so there would not be a public IP address that exists. RFC 1918 ensures the following ranges are for private network range usage:

• 10.0.0.0/8
• 172.16.0.0/12
• 192.168.0.0/16

In AWS routing wise it is possible to create a network range that overlaps with a public range, in this case the local network will always win.

Generally within AWS routing local will always have the highest priority, followed by more specific routes although this isn't always the case (for example in dynamic vs static routes).

Take a look at the routing priority documentation.