To get your answers quickly during the exam, you should use a chart that you've written down during the astronomy tutorial. A 1 - 126, N = 8 bits
B 128 - 191, N = 16 bits
C 192 - 223, N = 24 bits, where N = how many bits in Network ID
N + S + H = 32, where S = # of bits in Subnet ID, H = # of bits in Host ID # bits | subnet | # subnets | increment | | # hosts | = (2^H) - 2 | in mask (S) | mask | (2^S) - 2 | 256 - mask | A | B | C | 2 | 192 | 2 | 64 | 4M | 16K | 62 | 3 | 224 | 6 | 32 | 2M | 8K | 30 | 4 | 240 | 14 | 16 | 1M | 4K | 14 | 5 | 248 | 30 | 8 | 500K | 2K | 6 | 6 | 252 | 62 | 4 | 250K | 1K | 2 | 7 | 254 | 126 | 2 | 130K | 510 | --- | 8 | 255 | 254 | 1 | 65K | 254 | --- | You only need to remember a few things to derive the whole chart. The second column is the sum of 128 + 64, 128 + 64 + 32, 128 + 64 + 32 + 16, and so on
The third column is (2^S) - 2, starting with S = 2
The other columns can be derived through dividing by 2.
The last column is a reverse of the third column, starting with 62.
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