For the following subnets answer the following. How many subnets can there be an

Question

For the following subnets answer the following. How many subnets can there be and ow many hosts can be attached to each subnet. Class B address with 4 bits as subnet, 12 bits representing hosts. Class B address with 5 bits as subnet, 11 bits representing hosts. Class B address with 6 bits as subnet, 10 bits representing hosts. Class B address with 7 bits as subnet, 9 bits representing hosts. Class C address with 3 bits as subnet, 5 bits representing hosts. Class C address with 4 bits as subnet, 4 bits representing hosts.

Explanation / Answer

For better understanding and simplicity, lets start from the last question towards the first.

The default class C subnet mask is 255.255.255.0 , To make smaller networks (subnets), we borrow bits from the host portion of the mask. Since Class C mask uses only the last octet for host addressing, we only have 8 bits .

1.Class C address with 4 bits as subnet, 4 bits as representing hosts:

For the above question, mask can be represented as 255.255.255.240 (last octet as 1111000) . Number of 1's indicate subnet bits and number of 0's indicate host bits.

Number of subnets/hosts = 2x - 2 (since two of these subnets are not usable) where x is the number of 1's for subnets and x is number of 0's for the hosts.

The above equation for the current problem gives 24 - 2 = 14 subnets and 24 - 2 = 14 hosts for each subnet.

2. Class C address with 3 bits as subnet, 5 bits representing hosts

The subnet mask is 255.255.255.224 as the last octet binary is 11100000 .

Number of subnets = 23 - 2 = 6

Number of hosts per subnet = 25 - 2= 30 hosts

3. Class B address with 7 bits as subnets and 9 bits representing hosts

For Class B, default subnet mask is 255.255.0.0 , Class B has 16 bits to play with for creating the subnets

Class B with 7 bits as sunets and 9 represeting hosts can be represented as 255.255.254.0 where binary for the last two octets is 11111110.00000000

Number of subnets = 27 - 2 = 126

Number of host for each subnet = 29 - 2 = 510

4. Class B address with 6 bits as subnets and 10 bits representing hosts

binary for the last two octets : 11111100.00000000 , subnet mask is 255.255.252.0

Number of subnets = 26 - 2 = 62

Number of hosts for each subnet = 210 - 2 = 1022

5. Class B address with 5 as subnet and 11 represeting host bits

binary for the last two octets is 11111000.00000000 , subnet mask 255.255.248.0

Number of subnets = 25 - 2 = 30

Number of host for each subnet = 211 - 2 = 2046

6. Class B with 4 bits as subnet and 12 bits representing hosts

binary for the last two octets is 11110000.00000000 where as subnet mask is 255.255.240.0

Number of subnets = 24 - 2 = 14

Number of hosts for each subnet = 212 - 2 = 4094.

Hope the explanation is clear ! Let me know if you have any further doubts.

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