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Lab 3: VLSM
What is VLSM?
Variable Length Subnet Mask, VLSM is simply subnetting a subnet.
VLSM can be thought of as sub-subnetting.
We use VLSM to optimize IP addresses distribution
Why should we use it ?
Assume we have 4 group of users with: 1, 8, 16, and 4 with normal
subnets how many unused IP will we have?
Assume 5 groups: 2, 3, 4, 17, and 40!!
How to imagine it!
Remember from last lab that subnets blocks are of fixed size (thanks to
the power of 2!!) see this:
For class C:
1 bit for subnetting 7 bits for hosts : block size of 128
2 bit for subnetting 6 bits for hosts : block size of 64
3 bit for subnetting 5 bits for hosts : block size of 32
4 bit for subnetting 4 bits for hosts : block size of 16
5 bit for subnetting 3 bits for hosts : block size of 8
6 bit for subnetting 2 bits for hosts : block size of 4
Since we have we have 256 host, we can divide
Them to 2 subnets of 128, 128 assume we take
One of them and divide it to 2 subnets of size
64, 64 and so on!!
