I understand basic wildcard masking. 0.0.0.0 checks all bits, 255.255.255.255 checks none, and the combinations. What I don't understand is something like 0.0.15.255 . How do you block addresses from, say, host ranges between 16 and 25, but allow the rest. I know it relates to the bit pattern, but I just don't understand it. Any ideas?

Thanks to all that gave out advice!
I'll post tommorrow if I pass or fail.

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As far as I know, there's no way to block a range like 16-25, but you can do so with ranges like 16-31, 8-15, etc.
Let's assume you want to block an address range of x.x.x.16 to x.x.x.31. I'll just display the last octet:

16 - 00010000
31 - 00011111

As you can see, the first four bits in the last octet MUST be 0001. The last four bits can be any combination. So, to match the whole address up to the 28th bit, the wildcard mask is (for the last octet) 00001111 (decimal 15). So you have the complete wildcard mask as 0.0.0.15.

A quick way to figure out the mask is to subtract the upper limit from the lower limit (31 - 16 = 15.)

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