Subnetting Made Easy (Part 1)

Hello all,

in the standard subetting you have the classic table:

128 64 32 16 8 4 2 1

Another useful table could be:

128 192 224 240 248 252 254 255

From where 192 came?

192 is simply the sum of 128 and 64, infact 128 + 64 = 192

224 = 192 + 32

and so on..

So right now we know that:

/8 is 255.0.0.0
/16 is 255.255.0.0

and

/24 is 255.255.255.0

So what if we want to know /11?

What we need to do is really simple:

11 is between 8 and 16 so for sure the first otect will be 255, for the second otect:

11 – 8 is 3 and in the 3rd colon of our new table we’ll find 224; so /11 is 255.224.0.0

Let’s do /14:

14 – 8 = 6; 6th colon is 252 so /14 is 255.252.0.0.

What about /20?

For sure the first two otects will be 255.255 then 20 – 16 is 4 and 4th colon is 240; so /20 is 255.255.240.0

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