Your company has a remote office that contains 600 client computers on a single subnet.
You need to select a subnet mask for the network that will support all of the client computers. The solution must
minimize the number of unused addresses.
Which subnet mask should you select?
A.
255.255.252.0
B.
255.255.254.0
C.
255.255.255.0
D.
255.255.255.128
Confirmed.
2 bits from the 3rd octet and the whole of the last octet for the host id. 2^10=1024
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A
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Can anybody explain how to calculate this please.
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First of all you should convert the last octet to binary mode, for eaxmple 254=11111110 (please read how to convert decimal to binary)
255.255.254.0
it means 1111111 11111111 11111110 00000000
As you see we have nine of nulls
2^9=512 (it means if we have mask 255.255.254.0 we can create only 512 hosts)
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It means that correct ancwer is A
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to put it in laymen’s terms. you need 500 hosts, as in previous posts you have to do 2 to the power of 9. so you start with 2 then you just keep doubling until you get to over 500.
2,4,8,16,32,64,128,256,512.
we have had to double it 9x to get past 500.
so now you have to find the mask. easy as you should know 8 bits on add up to 255, you have had to take 9 bits to get the extra 500 host. so the for 4th octet it will be 0 as you have taken all 8 bits. this leaves you will 1 bite to take from the 3rd octet which will leave you will 252.
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255.255.255.0 / 24 => 256
255.255.254.0 / 23 => 512
255.255.252.0 / 22 => 1024 => 600 falls into this as > than 512 and 2048
255.255.240.0 / 20 => 4096
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Sorry Typo
255.255.252.0 / 22 => 1024 => 600 falls into this as > than 512 and 1024 addresses
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For a very quick and dirty answer:
Subtract the subnet mask from 256 and multiply by 256:
Examples:
256 – 255 = 256(1 * 256)
256 – 254 = 512 (2*256)
256 – 252 = 1024 (4*256)
And so on.
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A:
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