- Types of subnets:
- If a subnet's traffic is routed to an internet gateway the subnet is known as a public subnet.
- If a subnet doesn't have a route to the internet gateway the subnet is known as private subnet.
- The VPC is created with a master address range(CIDR block,can be anywhere from 16-28 bits) and subnet ranges are created within that range.
- New subnets are always associated with the default route table
- Once VPC is created you cannot change the CIDR block.
- You cannot created additional CIDR blocks that overlap with existing CIDR blocks
- You cannot create additional CIDR blocks in a different RFC 1918 range.
- Subnets with overlapping IP address ranges cannot be created
- The first 4 and last 1 IP address in a subnet are reserved.
- Subnets are created within AZs
- Subnets map 1:1 to AZs and cannot span AZs.