lly think the math is needed for the CCNA coursework, although Cisco makes you learn it. The CCIE exam does make you do bizarre things with subnet masks that require a full understanding of the math behind the topic. However, these things are rarely, if ever, seen in the real world, and are not a topic for this book. If you want to be able to do IP subnetting in your head, there are a couple of things you will need to understand. First, Cisco, along with every other major manufac- turer out there, wants you to learn subnetting its way. Why? So its tests are harder to pass, and SO everyone who's certified speaks the same language. Cisco, in particular, seems to want people to think in a way that makes it harder to figure out what's really going on. As an example, in Cisco parlance, a native class C network with a subnet mask of 255.255.255.224 is said to consist of 6 networks with 30 hosts in each network. Call me pedantic, but that's incorrect. The subnet mask actually results in 8 net- works with 32 hosts each. Cisco's point is that, using classful networking rules, there are only 6 available networks, with 30 available hosts in each network. While this is a valid concept, I believe it causes confusion. The reason Cisco's method causes confusion is simple: there is no easy way to prove the answer. Using the method I will outline here, however, there will always be an easy way to prove your answer. In this case, 8 * 32 = 256. Everything having to do with subnet masks has something to do with the number 256. In fact, this will be our first rule: Every result will either produce 256, or be divisible by 256. Looking at a subnet mask, the maximum value for an octet is 255. Remember, though, that the values start with 0, SO 255 is really the 256th number possible. This is a very important concept because everything else is predicated on this idea. The second rule astounds many people. In fact, it astounded me when I discovered it while writing my own subnet calculator program: Only nine values are possible for any oct