PowerShell Function to Extract Subnet/CIDR for a Pair of IP Addresses
Well, this one is hyper-specific... but in case anyone else needs to do something similar, I figure that I should share! As a tiny part of a much bigger project, one of my customers gave me a list of VLAN IDs and the IP Ranges that they want to use on each VLAN. Unfortunately, that list did not include either Subnet Mask or CIDR values, so I had to work backwards from the given ranges to determine what would be an acceptable Subnet Mask. This process involves some annoying binary math, so you know that I put together a script to do it for me! I wrote the extract-CIDR function to accept two IP Addresses, and then to output the smallest subnet/CIDR that could contain those two IP Addresses (so they don't technically need to be the start and end of the range, but it's safer to use those two). For example, if I give the script 192.168.0.1 and 192.168.0.254, I want to get back 192.168.0.0/24. If I'm playing around with subnets though, I want to be able to give it 192.168.1.