AmazonEC2Client.CreateSubnet Method (CreateSubnetRequest)

Creates a subnet in an existing VPC. You can create up to 20 subnets in a VPC. If you add more than one subnet to a VPC, they're set up in a star topology with a logical router in the middle. When you create each subnet, you provide the VPC ID and the CIDR block you want for the subnet. Once you create a subnet, you can't change its CIDR block. The subnet's CIDR block can be the same as the VPC's CIDR block (assuming you want only a single subnet in the VPC), or a subset of the VPC's CIDR block. If you create more than one subnet in a VPC, the subnets' CIDR blocks must not overlap. The smallest subnet (and VPC) you can create uses a /28 netmask (16 IP addresses), and the largest uses a /18 netmask (16,384 IP addresses).

IMPORTANT: AWS reserves both the first four and the last IP address in each subnet's CIDR block. They're not available for use.

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