not understand this QUestion ~ pls explain ~ Thanks

william_yeo

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

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

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

Thanks guys... finally i understood ~!