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Home > Archive > 70-088 > December 2000 > Subnetting Formula
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Subnetting Formula
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| Hi All,
I am going through MCSE Freak's subnetting guide, and just curious about one thing:
((2^2)-2)=2
Can someone explain this in detail for me?
Thanks.
rcwm | |
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| Your are borrowing bits. Look at your email, I sent you a good explanation for it. when you borrow bits in like this:
remember bits is borrowed from the 1st octets.
don't worry about 128 since that is supernetting and on the the test it is invalid. You are not tested on CNR(cisco).
192 Remember to use 2x2=4-2=2
224 2x2x2-2=6
240 2x2x2x2-2=14
248 2x2x2x2x2-2=30
252 2x2x2x2x2x2-2=62
254 2x2x2x2x2x2x2-2=126
255 2x2x2x2x2x2x2x2-2=254
class c address with .192 you can have 2 subnets and 62 host. easy way is to take .192 from 255 you get 63 that is your braodcast address. take 63-1 you get 62. that is your host. do the same with .224 take from 255 you get 31 your broadcast. 31-1= 30 host with 6 subnets. see the pattern. alttle trick if you take 62x4=248+6=254 that is your bottom number for class b. 254x2+2=510 is the next until you get to the top which is 16382, take that and 16382x4+6=65534 is the bottom number for class A. take that 65534x2+2=131,070 is the next, and so on..the chart would look like this:
mask Host C B A
192 2 2 62 16382 4194302
224 3 6 30 8190 2097150
240 4 14 14 4094 524,286
252 6 62 2 1022 262142
254 7 126 x 510 131,070
255 8 254 x 254 65534
Sorry for the long explanation got carried away.
[This message has been edited by seeker (edited 12-20-2000).] |
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