not understand this QUestion ~ pls explain ~ Thanks

william_yeo · October 2005

QUESTION NO: 20

Your network uses the172.12.0.0 class B address. You need to support 459 hosts per
subnet, while accommodating the maximum number of subnets. Which mask would you
use?

A. 255.255.0.0.
B. 255.255.128.0.
C. 255.255.224.0.
D. 255.255.254.0.

lordy · October 2005

The corrent answer is D.

The next power of 2 bigger then 459 (the required number of hosts) is 512.

The netmask for 512 hosts is 255.255.254.0

Using this netmask leaves the maximum number of subnets.

HTH,
Lordy

SV · October 2005

2^n-2= 459
2^n = 461 (the next value that could be used is 512)
2^n = 512
Since n = 9, the number of bits to be used for host bits are 9.
11111111.11111111.11111110.00000000

Therefore the mask is 255.255.254.0

william_yeo · October 2005

Thanks guys... finally i understood ~!

not understand this QUestion ~ pls explain ~ Thanks

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