Subnet is short for subnetwork. As we saw at the beginning of this chapter, a network is subdivided into multiple logical parts for controlling access to individual logical subparts of the network. When we create a subnet, we need to specify a unique CIDR block for the subnet. This CIDR block has to be a subset of the VPC CIDR block. Each subnet must reside entirely within a single AZ as a subnet cannot span multiple AZs.
Subnets are categorized as public and private subnets based on their security profile, or in other words, based on their route table. We will now discuss different types of subnets.
