genXrcist wrote: » Answer C meets all the objectives. It is a Classfull address range that can handle all the numbers thrown at us in the question. 20 sites at 2-250 nodes each can be accomplished with the following: 172.20.160.0/23 D is wrong because when you subnet a Classfull C address, the 4th octet is the interesting octet. Your example is subnetting the 3rd octet, which is not Class C. C is right because we subnet the 3rd octet, which you can do and still maintain the Class B status. I think B is wrong because you'll be subnetting the 3rd octet anyway to keep the network managable that you might as well use the Class B.