Seriously it really is easier than it looks—really! I could certainly go through the binary math for you, but no one needs that. Actually, all you have to do is remember that the wildcard is always one number less than the block size. So, in our example, the wildcard would be 7 since our block size is 8. If you used a block size of 16, the wildcard would be 15. Easy, huh? But just in case, we’ll go through some examples to help you nail it. The following example tells the router to match the first three octets exactly but that the fourth octet can be anything :