Calculating hosts / subnets over 8 bits.

Hey guys,
I have been going through some sub netting before I sit my intro exam, I am having trouble calculating the total number of host or subnets over 8 bits. I have been using the rule of 2 to the power total number of bits and then minus two (for hosts) I find this extremely hard to figure out with just with the shear size of the numbers.
Do you guys have any tips? I am considering memorizing the combinations.
Any help would be great
Thanks
Nick

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Comments

techster79

If it is close to 8, for example 11, just take 256 and double it 3 times...

9=512
10=1024
11=2048

It is easy to remember that 10 bits = 1024 so start there if the number is much higher. You should have the values memorized so you can count on your fingers like this:

1=2
2=4
3=8
4=16
5=32
6=64
7=128
8=256
9=512
10=1024
now start over counting with 11
11=2048
12=4096
13=8192(most likely will never need to count this high)
14=16384
15=32768
16=65536(definitely won't go higher than this)

baldychoko

Thanks mate, i thought that would be the best way to go.
Nick