Ip addressing is a critical topic to spend time on. That's the whole deal! To get good with it just takes time and practise and playing with the numbers and conversions. There are, after all on 256 numbers one has to memorize the binary conversion for if they want to go the memorization route and be quick at it... but as far as subnetting goes there is only 7 and those are the really critical ones to be able to do at the drop of a hat.

0 masked bits = the network number (only used w/VLSM)
1 masked bits = 128
2 masked bits = 192
3 masked bits = 224
4 masked bits = 240
5 masked bits = 248
6 masked bits = 252
7 masked bits = 254
8 masked bits = 255 -> the broadcast addy for the network

subnet masks will have one of those numbers as the last octet



Thanks for your post MtnMan....this is the kind of topic that people need to have presented to them many times in many different ways. It's the "hard" that makes it great! If it looked too easy then everyone could understand it and those of us who've spent time with it would be less mysterious to the sales and marketing types.