According to AWS documentation, subnets are nothing but a range of IP addresses in your VPC. It is possible to launch the resources of AWS into your desired subnet. For resources that need internet access, you can use a public subnet. Whereas for resources that don’t need the internet, a private subnet is sufficient.
The default subnet in your VPC must have the netmask value 20 that can give up to 4096 addresses per subnet. The subnet is always confined within a single availability zone whereas VPC can span across multiple zones.
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