I’m a sysadmin/consultant by trade. I cut my teeth on IPv4 addressing way back in the NT4 days when most addressing was still class based.
I never really got the hang of CIDR addressing but I understood the rationale and concepts of it. I was never very good at finding a good approach to subnetting and CIDR mask determination though. Usually there was a network person’s brain handy to have a conversation with and that got me by.
Then along came public Cloud and the rules for CIDR address allocation and subnetting changed again. I knew that the old approach to subnet determination wasn’t really good for the public Clouds and all the docs from the vendors wanted you to assign a /16 to every VPC/vNet you created. This always felt wasteful and like overkill to me.
I decided to hunt around for something that could help me and found this tool. Visual Subnet Calculator