Part $3-$ Subnetting a Class B block

Suppose we're an organisation with a class B block available, let's say $155\mathrm{.}155\mathrm{.}0\mathrm{.}0/16.$ We have branches

in multiple cities, and want to split this address space into subnets to allocate to separate branches. We

want each branch to have enough addresses for $2000$ hosts. How should we subnet in this case?

A subnet size can only be a power of $2,$ so we need to find the next largest power of two: $2^{11}=2048.$ This

means we need to leave $11$ host bits $(H=11).$ We start with a class B block, so $N=16,$ and we know $N+S$

$+H=32,$ so a little bit of algebra gives us $S=5,$ so we're borrowing $5$ bits for subnetting. In slash notation,

our subnet mask will be $\frac{?}{21(16+5)},$ which in octet notation is $11111111,11111111\mathrm{.}11111000\mathrm{.}00000000=$

$255\mathrm{.}255\mathrm{.}248\mathrm{.}0.$

This creates $32(2^5)$ subnets as follows:

When working out subnetting for subnets of size more than $256,$ it can be simpler to think in terms of the

number of class C blocks. Notice that $2048=8256,$ so each of our subnets is equivalent $8$ class $C$

blocks. The subnet mask is $255\mathrm{.}255\mathrm{.}248.,$ and $248=256-8.$ Each of our subnets begins at an address

where the third octet is a multiple of $8.$

Task $3$

Consider the scenario above, but suppose we need to accommodate $3000$ hosts per subnet.

A$.$ What subnet size do we need? What are $S$ and $H$ in this case?

B$.$ How many subnets of this size can we create in the class B block?

C$.$ What is the subnet mask?

D$.$ Complete the table below to show the details for the first three of the subnets: