Question

Could anyone explain how we get these numbers

Given 172.16.0.0/16 your Network needs to accommodate 1000 sales department users, 1023 Workstations, 8 Managers, and 200 staff. Given 192.168.1.0/24 your Network needs to accommodate 4 Managers, 120 Users, and 32 staff. What would be the Next IP address if you needed to expand on your scheme.

Answer 1

Part 1

172.16.0.0/16

Step 1: Arrange number of clients per group in descending order and determine how many bits required to accommodate them

1023      -- 11bits(since we might have two preassigned addresses for Network and Broadcast)

1000    -- 10bits

200    -- 8bits

8     -- 4bits(since we might have two preassigned addresses for Network and Broadcast)

Since we have 16 bit mask we have 16 (32-16) more bits at our disposal.

Step 2: Assign the largest group with an address such that last n bits are 0 (mark that we got n from step 1) and no group address space overlap

1023:   00000000 00000000
1000:    00001000 00000000 ← Note that we changed 11th bit from right to 1 so that it does not overlap

200:    00001100 00000000← Note that we changed 12th bit from right to 1 so that it does not overlap with the above two.

8:    00001101 00000000 ← Note that we changed 12th and 9th bit from right to 1 so that it does not overlap with the above three.

I think now you can guess why on the first hand I asked you to arrange the groups in descending order of their size. If we have done in ascending order, we would have had a tough time assigning the addresses

Therefore we have

Size         Network Address    Mask
1023        172.16.0.0        /23
1000        172.16.8.0        /22

200        172.16.12.0        /24

8        172.16.13.0        /28

Note that Mast = 32-n, where n is number of bits required.
    And 1st 16 bits remains same i.e. 172.16 in our case

Part 2.

192.168.1.0/24

Groups:

120    -- 7bits

32     -- 6bits

4    -- 3bits

We have 8 bits at our disposal (32-24 = 8)

120:    00000000
32:    10000000
4:    11000000

Therefore we have

Size         Network Address    Mask
120        192.168.1.0        /25
1000        192.168.1.128        /26

200        192.168.1.192        /29

I tried my best to keep the answer as simple as possible but also descriptive at the same time. I hope you like the way I answered. Incase you need more clarification, please let me know through the comment section below. I shall be glad to help you with the same.