How does Subnetting Work, and How do you do it by hand or in your head? Can someone explain both conceptually and with several examples? Server Fault gets lots of subnetting homework questions, so we could use an answer to point them to on Server Fault itself.

• What is classless routing and why is class-based routing obsolete?
• If I have a network, how do I figure out how to split it up?
• If I am given a netmask, how do I know what the network Range is for it?
• Sometimes there is a slash followed by a number, what is that number?
• Sometimes there is a subnet mask, but also a wildcard mask, they seem like the same thing but they are different?
• Someone mentioned something about knowing binary for this?

Not looking for links to other sites (unless maybe you have one post with a bunch of good ones).

I already know how to subnet, I just thought it would be nice if Server Fault had a generic subnetting answer.