In a VPC with a CIDR block of 172.16.1.0/16, what is required for all resources to communicate locally?

For all resources within a Virtual Private Cloud (VPC) to communicate locally, a route table with local routes is essential. In a VPC, the local route allows instances in the same VPC to communicate with each other irrespective of subnet boundaries, as long as they are associated with the same CIDR block.

In a setup where the CIDR block is 172.16.1.0/16, this means that any IP address within the range of 172.16.1.0 to 172.16.1.255 can communicate with one another without restrictions from external network routes. The default route for a VPC automatically includes a route to the local CIDR block, facilitating communication among all descendants within that range.

While other components like a public gateway, a local security group, or a NAT gateway might serve specific networking purposes, they do not play a direct role in ensuring local communication among resources within the VPC. A public gateway allows instances to connect to the internet, a NAT gateway is used primarily for outbound internet access for instances in private subnets, and security groups control inbound and outbound traffic rather than enabling basic local communication.