RegEx shortcuts for working with Classless Internet Domain Routing (CIDR)

I haven’t seen these posted anywhere, so I figured I would share. Here are some RegEx shortcuts for working with various CIDR blocks. They aren’t the most concise, but they are readable which is important to me when cobbling together complex combinations. They are POSIX regex so they should work in a bunch of places like egreps and MySQL REGEXPs.