Subnetting a Class C Network Using Binary

Last Updated on Tue, 03 Oct 2023 | Portable Command

You have a Class C address of 192.168.100.0 /24. You need nine subnets. What is the IP plan of network numbers, broadcast numbers, and valid host numbers? What is the subnet mask needed for this plan?

You cannot use N bits, only H bits. Therefore, ignore 192.168.100. These numbers cannot change.

Step 1 Determine how many H bits you need to borrow to create nine valid subnets. 2n- 2 > 9

N = 4, so you need to borrow 4 H bits and turn them into N bits.

Start with 8 H bits

HHHHHHHH

Borrow 4 bits

NNNNHHHH
Step 2 Determine the first valid subnet in binary.

0001HHHH

Cannot use subnet 0000 because it is invalid. Therefore, you must start with the bit pattern of 0001

00010000

All 0s in host portion = subnetwork number

00010001

First valid host number

00011110

Last valid host number

00011111

All 1s in host portion = broadcast number

Step 3 Convert binary to decimal.

00010000= 16

Subnetwork number

00010001= 17

First valid host number

00011110=30

Last valid host number

00011111=31

All 1s in host portion = broadcast number

Step 4 Determine the second valid subnet in binary.

0010HHHH

0010 = 2 in binary = second valid subnet

00100000

All 0s in host portion = subnetwork number

00100001

First valid host number

00101110

Last valid host number

00101111

All 1s in host portion = broadcast number
Step 5 Convert binary to decimal.

00100000 = 32

Subnetwork number

00100001 = 33

First valid host number

00101110=46

Last valid host number

00101111=47

All 1s in host portion = broadcast number
Step 6 Create an IP plan table.

Valid Subnet

Network Number

Range of Valid Hosts

Broadcast Number

1

16

17-30

31

2

32

33-46

47

3

48

49-62

63

Notice a pattern? Counting by 16. Step 7 Verify the pattern in binary. (The third valid subnet in binary is used here.)

0011HHHH

Third valid subnet

00110000=48

Subnetwork number

00110001=49

First valid host number

00111110=62

Last valid host number

00111111=63

Broadcast number
Step 8 Finish the IP plan table.

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Readers' Questions

  • fatima robertson
    Which class of ip address follows the pattern network.network.network.host?
    10 months ago
    • Class C IP address
    • Dennis
      What is the broadcast address for a class c network?
      10 months ago
      • The broadcast address for a Class C network is the third and fourth octet of the IP address with all bits set to 1 (255.255.x.255).
      • MICHAEL
        How to do subnetting for class c?
        1 year ago
        • Subnetting a Class C network involves breaking a single network into multiple networks or subnets. This is usually done to increase the number of hosts on a single network by dividing the current IP addresses into smaller groups. To subnet a class C network, you need to identify the following elements: 1. The network address 2. The subnet mask 3. The number of subnets 4. The number of hosts per subnet Once you determine the above elements, you can divide the IP addresses in the network using an appropriate subnet mask.
        1. Calculate the number of bits needed to represent the number of subnets. This number is found by taking the log base 2 of the number of subnets.
        2. Determine the number of host bits that are required. This number can be found by subtracting the number of subnet bits from 8.
        3. Calculate the subnet mask based on the number of subnet and host bits.
        4. Create the subnets by using the subnet mask to identify the network address of each subnet.
        5. Divide the IP addresses into the newly created subnets.Once you have completed the above steps, you should have successfully subnetted the Class C network.

        Subnet

        Network Address (0000)

        Range of Valid Hosts (0001-1110)

        Broadcast Address (1111)

        0(0000) invalid

        192.168.100.0

        192.168.100.1192.168.100.14

        192.168.100.15

        1(0001)

        192.168.100.16

        192.168.100.17192.168.100.30

        192.168.100.31

        2(0010)

        192.168.100.32

        192.168.100.33192.168.100.46

        192.168.100.47

        3(0011)

        192.168.100.48

        192.168.100.49192.168.100.62

        192.168.100.63

        4(0100)

        192.168.100.64

        192.168.100.65192.168.100.78

        192.168.100.79

        5(0101)

        192.168.100.80

        192.168.100.81192.168.100.94

        192.168.100.95

        6(0110)

        192.168.100.96

        192.168.100.97192.168.100.110

        192.168.100.111

        7(0111)

        192.168.100.112

        192.168.100.113192.168.100.126

        192.168.100. 127

        8(1000)

        192.168.100.128

        192.168.100.129192.168.100.142

        192.168.100. 143

        9(1001)

        192.168.100.144

        192.168.100.145192.168.100.158

        192.168.100.159

        10 (1010)

        192.168.100.160

        192.168.100.161192.168.100.174

        192.168.100.175

        11 (1011)

        192.168.100.176

        192.168.100.177192.168.100.190

        192.168.100.191

        12 (1100)

        192.168.100.192

        192.168.100.193192.168.100.206

        192.168.100. 207

        13 (1101)

        192.168.100.208

        192.168.100.209192.168.100.222

        192.168.100. 223

        14 (1110)

        192.168.100.224

        192.168.100.225192.168.100.238

        192.168.100. 239

        15 (1111) invalid

        192.168.100.240

        192.168.100.241192.168.100.254

        192.168.100. 255

        Quick Check

        Always an even number

        First valid host is always an odd #

        Last valid host is always an even #

        Always an odd number

        Use any nine subnets—the rest are for future growth.

        Use any nine subnets—the rest are for future growth.

        Step 9 Calculate the subnet mask.

        The default subnet mask for a Class C network is as follows:

        Decimal

        Binary

        255.255.255.0

        11111111.11111111.11111111.00000000

        1 = Network or subnetwork bit 0 = Host bit

        You borrowed 4 bits; therefore, the new subnet mask is the following:

        11111111.11111111.11111111.11110000

        255.255.255.240

        NOTE: You subnet a Class B or a Class A network with exactly the same steps as for a Class C network; the only difference is that you start with more H bits.

        Continue reading here: Subnetting a Class B Network Using Binary

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