Subnet Mask Cheat Sheet - A Tutorial and Thorough Guide to Subnetting!
Subnet Cheat Sheet PDF (Become a Subnetting Master)
Dan York on Twitter: "Nice cheat sheet for #IPv4 subnetting (and a good reminder that if you move to #IPv6 you don't have to worry as much about all these smaller subnets
Subnet Mask Reference Table | Brain Knowledge
Subnet Mask Cheat Sheet - The Cisco Learning Network