question on subnetting...

[kisa]

Originally Posted by zoltron30

in sir lammles ccna 5th edition hard cover book on page 131 he shows a subnetting example. practice example #7b: 255.255.255.192/26. but how does mr lammle get 2^10? where does the 10 come from? because on page 129 example 3b:255.255.255.240.0 it shows 2^4 which makes sense to me.

thanks!

Hi

I know the fever and confusion that is always hitting us new subnetting starters. I have seen where you query is, but this is what I can offer,
PRACTICE EXAMPLE 7B
255.255.255.192 (/26) 172.16.0.0

By default a class B subnet Mask is 255.255.0.0 which is 16 bits (255.255)for the network and 16 bits (0.0) for the Hosts. The /26 means that more bits have been borrowed from the host bits

Host: 00000000 . 00000000 this means 16 bits by default plus (+) 10 bit Red will give a total of /26 bits. 26 - 16 (default) = 10 and count 10 zeros from left to right.

And the formula to find the number of networks/subnets is 2^10 (the red 0's) = 1024
The Host will be 2^6-2 (the six remaining 0') = 64-2=62
And the Increment/block size is 64. Why? This is the smallest number on the borrowed bits of the forth Octet.

128 64 32 16 8 4 2 1
0 0 0 0 0 0 0 0

Or as Lammle shows us is 256-192=64

But being a beginner 'am still finding problems with Class B and A.
Hope when you get better you will help me.
Thanks