[swinglock]

Look up CIDR on Wikipedia, which is what we use now and you know it already, but more so to learn the difference from the old classful networking.

Then you'll never use "Class A/B/C" again. :) It's correct to just say /24 while Class C isn't, because it has a more specific but outdated meaning.

[tptacek]

I'm familiar with CIDR, I just always understood it to mean "arbitrary prefix lengths, not just on byte boundaries".