Answer & Explanation:
An IP version 4 address is of the form w.x.y.z/s
where s = subnet mask
w = first 8 bit field, x = 2nd 8 bit field, y = 3rd 8 bit field, and z = 4th 8 bit field
each field has 256 decimal equivalent. that is
binary denary or decimal
11111111 = 2⁸ = 256
w.x.y.z represents
in binary
11111111.11111111.11111111.11111111
in denary
255.255.255.255
note that 255 = 2⁸ - 1 = no of valid hosts/addresses
there are classes of addresses, that is
class A = w.0.0.0 example 10.0.0.0
class B = w.x.0.0 example 172.16.0.0
class C = w.x.y.0 example 198.16.8.1
where w, x, y, z could take numbers from 1 to 255
Now in the question
we were given the ip address : 198.16.0.0 (class B)
address of quantity 4000, 2000, 8000 is possible with a subnet mask of type
255.255.0.0 (denary) or
11111111.11111111.00000000.00000000(binary) where /s = /16 That is no of 1s
In a VLSM (Variable Length Subnet Mask)
Step 1
we convert the number of host/addresses for company A to binary
4000 = 111110100000 = 12 bit
step 2 (subnet mask)
vary the fixed subnet mask to reserve zeros (0s) for the 12 bit above
fixed subnet mask: 11111111.11111111.00000000.00000000 /16
variable subnet mask: 11111111.11111111.11110000.000000 /20
now we have added 4 1s in the 3rd field to reserve 12 0s
<u><em>subnet mask: 255.255.</em></u><u><em>16.</em></u><u><em>0 (where the 1s in each field represent a denary number as follows)</em></u>
<u><em>1st 1 = 128, 2nd 1 = 64 as follows</em></u>
<u><em>1 1 1 </em></u><u><em> 1 </em></u><u><em> 1 1 1 1</em></u>
<u><em>128 64 32 </em></u><u><em>16</em></u><u><em> 8 4 2 1</em></u>
step 3
in the ip network address: 198.16.0.0/19 <em>(subnet representation)</em> we increment this using 16
that is 16 is added to the 3rd field as follows
That means the ist Valid Ip address starts from
Ist valid Ip add: 198.16.0.1 - 198.16.15.255(last valid IP address)
Company B starts<u><em>+16: 198.16.</em></u><u><em>16</em></u><u><em>.0 - 198.16.31.255</em></u>
<u><em> +16: 198.16.</em></u><u><em>32</em></u><u><em>.0- 198.16.47.255 et</em></u>c
we repeat the steps for other companies as follows
Company B
Step 1
we convert the number of host/addresses for company B to binary
2000 = 11111010000 = 11 bit
Step 2
vary the fixed subnet mask to reserve zeros (0s) for the 11 bit above
fixed subnet mask: 11111111.11111111.00000000.00000000 /16
variable subnet mask: 11111111.11111111.11111000.000000 /21
now we have added 5 1s in the third field to reserve 11 0s
<u><em>subnet mask: 255.255.</em></u><u><em>8.</em></u><u><em>0 (where the 1s in each field represent a denary number as follows)</em></u>
<u><em>1st 1 = 128, 2nd 1 = 64 as follows</em></u>
<u><em>1 1 1 1 </em></u><u><em>1 </em></u><u><em> 1 1 1</em></u>
<u><em>128 64 32 16 </em></u><u><em>8 </em></u><u><em> 4 2 1</em></u>
Step 3
Starting from after the last valid Ip address for company A
in the ip network address: 198.16.16.0/21 (<em>subnet representation</em>) we increment this using 8
That means the ist Valid Ip address starts from
Ist valid Ip add: 198.16.16.1 - 198.16.23.255(last valid IP address)
Company C starts <u><em>+16: 198.16.</em></u><u><em>24</em></u><u><em>.0- 198.16.31.255</em></u>
<em> </em><u><em> +16: 198.16.</em></u><u><em>32</em></u><u><em>.0- 198.16.112.255 et</em></u>c
Company C
Step 1
we convert the number of host/addresses for company C to binary
4000 = 111110100000 = 12 bit
Step 2
vary the fixed subnet mask to reserve zeros (0s) for the 12 bit above
fixed subnet mask: 11111111.11111111.00000000.00000000 /16
variable subnet mask: 11111111.11111111.11110000.000000 /20
now we have added 4 1s in the 3rd field to reserve 12 0s
<u><em>subnet mask: 255.255.</em></u><u><em>16.</em></u><u><em>0 (where the 1s in each field represent a denary number as follows)</em></u>
<u><em>1st 1 = 128, 2nd 1 = 64 as follows</em></u>
<u><em>1 1 1 1 1 1 1 1</em></u>
<u><em>128 64 32 16 8 4 2 1</em></u>
Step 3
Starting from after the last valid ip address for company B
in the ip network address: 198.16.24.0/20 (subnet representation) we increment this using 16
That means the ist Valid Ip address starts from
Ist valid Ip add: 198.16.24.1 - 198.16.39.255(last valid IP address)
Company C starts <u><em>+16: 198.16.40.0- 198.16.55.255</em></u>
<em> </em><u><em> +16: 198.16.56.0- 198.16.71.255 et</em></u>c
Company D
Step 1
we convert the number of host/addresses for company D to binary
8000 = 1111101000000 = 13 bit
Step 2
vary the fixed subnet mask to reserve zeros (0s) for the 13 bit above
fixed subnet mask: 11111111.11111111.00000000.00000000 /16
variable subnet mask: 11111111.11111111.11100000.000000 /19
now we have added 3 1s in the 3rd field to reserve 13 0s
<u><em>subnet mask: 255.255.</em></u><u><em>32.</em></u><u><em>0 (where the 1s in each field represent a denary number as follows)</em></u>
<u><em>1st 1 = 128, 2nd 1 = 64 as follows</em></u>
<u><em>1 1 </em></u><u><em> 1 </em></u><u><em> 1 1 1 1 1</em></u>
<u><em>128 64 </em></u><u><em>32 </em></u><u><em> 16 8 4 2 1</em></u>
Step 3
Starting from after the last valid ip address for company C
in the ip network address: 198.16.40.0/20 (subnet representation) we increment this using 32
That means the ist Valid Ip address starts from
Ist valid Ip add: 198.16.40.1 - 198.16.71.255(last valid IP address)
Company C starts <u><em>+16: 198.16.72.0- 198.16.103.255</em></u>
<em> </em><u><em> +16: 198.16.104.0- 198.16.136.255 et</em></u>c