One of the conveniences in using Excel spreadsheets is that you can color the subnets thereby you would know the range (useful for VLSM). Example for given class C (256 cells) -- you would color the first 4 cells for a /30 subnet. Then if the next subnet is /29, you would fill the next 8 cells with a different color. I hope there is a feature in IPPlan where you can choose a color from a palette to fill the cells based on the subnet range. Cheers!