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Subnetting question

By ans_84 ·
How do i find out the subnet mask when i only got an IP range? (ex: I already got the answer, please give me an explanation.

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Some links

by NickNielsen In reply to Subnetting question
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by ans_84 In reply to Some links

I think i?ve already got a good understandin of binarys. It was just this issue i couldn?t find out! Thanks for the links anyway.

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S'all right

by NickNielsen In reply to Re:

It seems I misunderstood your question.

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Quick and dirty

by crt In reply to Subnetting question

You should know that the maximum value per octet is 255 so you go octet by octet and take the difference between the 2 values and substract that from 255:

First octet = 207 and 207, diff = 0 so mask value = 255 - 0 = 255
Second octet = 46 and 46, diff = 0 so mask value = 255 - 0 = 255
Third octet = 200 and 207, diff = 7 so mask value = 255 - 7 = 248
Fourth octet = 0 and 255, diff = 255 so mask value = 255 - 255 = 0

Which gives you a mask of

(Of course since bits have to be contiguous in a subnet mask once you find a non-255 value you don't have to calculate the remaining octet(s) as everything that follows has to be 0)

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Thank you!

by ans_84 In reply to Quick and dirty

Thanks for your very good explanation of this issue! It seems to be quite simple after all!

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by ramzeelali In reply to Subnetting question

u give the ip range from to
first understand that it as a class C ip address
find out the changes b/w 2 ip address
A.B.C.D ie A=207 B=46 C=200 to 207 & D=0 to 255
first changes started from c (200 to 207)
therefore subnet mask is 255.255._.0 for A&B
for c there is 8 is the difference(256-248=8 OR 256-8=24
there for by adding the 248 for C we get

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