Is AWS VPC CIDR shared with other accounts?

Question

AWS creates default VPC with CIDR 10.0.0.0/16 or sometimes 172.31.0.0/16.

I created another AWS account & in that also same CIDR blocks were created.

So my question is

1. If 2 accounts have same CIDR blocks then is my number of subnets available shared by other accounts?
2. For for application, should I create my own VPC rather than using default one created by AWS?

Appreciate an answer

Answer 1

Two VPCs whether in the same account or different account can have the same CIDR BUT you cannot route traffic between them. ie., if the instances in the VPCs do not communicate.

If you really want to route traffic between them using internal IPs (using VPN etc.,) you MUST use a different CIDR, same account or different account does not matter.

If you have the same CIDR, the routing table will route the traffic internally when you intend to route it to the other VPC.