Question

Scenario 2 (Use the network 192.126.100.0 for the following questions.) 9) I want to break up my network into subnets for some workgroups. Each workgroup has 12 hosts, what is the maximum # of subnets can I create that will support at least 12 hosts per subnet? 10) What will the subnet mask be? 11) Give the network, IP range, and broadcast address for the first 3 networks: Network 1: Broadcast: Host IP Range: to Network 2: Broadcast: Host IP Range: to Network 3: Broadcast: Host IP Range: to

Answer 1

The given network = 192.126.100.0

Since nothing is mentioned about type of IP Addressing, it is assumed to be Classful IP Addressing. The first octet value 192 falls in the range 192 - 223 which is range of IP Addresses supported by Class C. So the given IP Address 192.126.100.0 belongs to Class C.

As per Class C, the first three octets belongs to Network ID and last octet is alloted to Host ID. So to create subnets, the bits to be alloted to subnet must be taken from Host ID and the remaining bits of Host ID will be alloted to hosts within subnets. The binary notation for given network is

11000000.01111110.01100100.00000000

It is given that each subnet should have atleast 12 hosts. But the number of hosts are generally alloted in powers of 2. So the number closest to 12 and representable in power of 2 is 16. So for representing 16 IP Address, log₂16 = log₂2⁴ = 4 bits are needed. So least signiifcant four bits in last octet 00000000 are allocated to Host ID and most significant 4 bits will be alloted to Subnet ID.

192.126.100.00000000 Host ID Subnet ID

(9) The possible values of Host ID portion will be from 0000 (0) to 1111 (15). Similarly the possible values for Subnetwork ID will be from 0000(0) to 1111(15).The number of possible subnets will be from Subnet 0 to Subnet 15 = 16 Subnets. So 16 Subnets will be possible in total.

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(10) A mask can be defined as the bits that are being required. Networks that are not subnetted will have default mask which contains 1's in Network ID portion and 0's in Host ID portion. Since given network is Class C, the default mask of the given network without subnetting will be

            11111111.11111111.11111111.00000000

     i.e.,   255.255.255.0

In /n notation it can be represented as /24 where n is number of bits in Network ID part. The Subnet mask is combination of default mask of the network combined with subnet bits. It means when an network is subnetted along with original Network ID, the subnet portion also will contain 1's and Host ID bits will contain 0's as usual. So the subnet mask will be

            11111111.11111111.11111111.11110000

      i.e.,The Subnet mask of the network is 255.255.255.240

In /n notation the entire network with subnets can be represented as 192.126.100.0/28 ( considering Classful Addressing ) where n represents bits of the subnetwork portion.

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(11) The entire information of each subnet is listed below :

Subnet	First IP Address	Last IP Address	First Host Address	Last Host Address
0	192.126.100.0	192.126.100.15	192.126.100.1	192.168.100.14
1	192.126.100.16	192.126.100.31	192.126.100.17	192.126.100.30
2	192.126.100.32	192.126.100.47	192.126.100.33	192.126.100.46
3	192.126.100.48	192.126.100.63	192.126.100.49	192.126.100.62
4	192.126.100.64	192.126.100.79	192.126.100.65	192.126.100.78
5	192.126.100.80	192.126.100.95	192.126.100.81	192.126.100.94
6	192.126.100.96	192.126.100.111	192.126.100.97	192.126.100.110
7	192.126.100.112	192.126.100.127	192.126.100.113	192.126.100.126
8	192.126.100.128	192.126.100.143	192.126.100.129	192.126.100.142
9	192.126.100.144	192.126.100.159	192.126.100.145	192.126.100.158
10	192.126.100.160	192.126.100.175	192.126.100.161	192.126.100.174
11	192.126.100.176	192.126.100.191	192.126.100.177	192.126.100.190
12	192.126.100.192	192.126.100.207	192.126.100.193	192.126.100.206
13	192.126.100.208	192.126.100.223	192.126.100.209	192.126.100.222
14	192.126.100.224	192.126.100.239	192.126.100.225	192.126.100.238
15	192.126.100.240	192.126.100.255	192.126.100.241	192.126.100.254

It can be observed that in every subnet 16 IP Address are possible but only 14 can be allocated to the hosts. Because the first IP Address of a Subnet is the Network ID of the Subnet and last IP Address will act as Directed Broadcast Address (DBA) of the Subnet.

The information about first three networks is given below :

Subnet	First IP Address	Last IP Address	Host IP Address Range	Network ID	BroadCast Address
0	192.126.100.0	192.126.100.15	192.126.100.1 to 192.168.100.14	192.126.100.0	192.126.100.15
1	192.126.100.16	192.126.100.31	192.126.100.17 to 192.126.100.30	192.126.100.16	192.126.100.31
2	192.126.100.32	192.126.100.47	192.126.100.33 to 192.126.100.46	192.126.100.32	192.126.100.47

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