Let me respond to Chuck with an example, just for clarity's sake: EXXON, the gas folks, come to you and request a /20. They are using this /20 internally (say, to assign IP addresses to individual gas pumps across the US). They demonstrate to you that they are going to number 1,024 pumps upon the receipt of this /20. They demonstrate to you that they plan to number 2,048 pumps total over the next 12 months. A few months go by, and EXXON comes to you and says that they have number 3,400 pumps, and are now over 80% utilized on the initial /20 you assigned them. You can now assign them additional address space. You are not really justified to assign more address space to them until they have assigned 80% of their /20. (There are real-world examples where orgs need to request additional address space at the same time as achieving 80%, but let's not let reality get in the way of textbook examples!) The size of the additional block you assign them should closely fit the 25%-50% requirement. (Again, real world examples tend to trend to fitting the 50% requirement more than the 25% requirement, but so be it.) /david