burleyman1 sent this link out to LinkedIn’s Cisco Certifications group:
Subnetting, love it or hate it if you are in the networking field it needs to become your friend. I have gone over a bunch of “easy” ways to learn subnetting and wildcard masks and to be honest some of them confused the heck out of me. So what I have written down is something I put together that helped me get it and to be able to do subnetting quicker and in a lot of cases in my head. So here it is, please let me know if this was helpful or confusing.
In subnetting the only thing you really need to memorize is…..
And then he goes through a simple way of finding the Magic Number (256 – subnet mask), and then subtract 2 to find the number of possible hosts on that mask.