Explained: CIDR

You spin up a VPC in AWS and it asks for a CIDR block. You type 10.0.0.0/16 because that's what the tutorial said. Then you create a subnet and it wants another one, so you put 10.0.1.0/24 . It works. You move on. Six months later somebody asks why the subnet can only hold 251 usable addresses when you asked for 256, and whether 10.0.1.0/24 overlaps with the 10.0.0.0/22 block the networking team just allocated. You don't know. Nobody does.… Read More