Defining Host Addresses for Each Subnet

In this example there are 7 bits in the host number field of each subnet

address, which means that each subnet represents a block of 126 host

addresses. The hosts on each subnet are numbered 1 through 126. 

The valid host addresses for Subnet #3 are listed in the following sam 

ple code. The underlined portion of each address identifies the

extended network prefix, while the bold digits identify the 7 bit host

number field: 

Subnet #3: 10001100.00011001.00000001.1 0000000 = 140.25.1.128/25

Host #1: 10001100.00011001.00000001.1 0000001 = 140.25.1.129/25

Host #2: 10001100.00011001.00000001.1 0000010 = 140.25.1.130/25

Host #3: 10001100.00011001.00000001.1 0000011 = 140.25.1.131/25

Host #4: 10001100.00011001.00000001.1 0000100 = 140.25.1.132/25

Host #5: 10001100.00011001.00000001.1 0000101 = 140.25.1.133/25

Host #6: 10001100.00011001.00000001.1 0000110 = 140.25.1.134/25

.

.

Host #62: 10001100.00011001.00000001.1 0111110 = 140.25.1.190/25

Host #63: 10001100.00011001.00000001.1 0111111 = 140.25.1.191/25

Host #64: 10001100.00011001.00000001.1 1000000 = 140.25.1.192/25

Host #65: 10001100.00011001.00000001.1 1000001 = 140.25.1.193/25

.

.

Host #123: 10001100.00011001.00000001.1 1111011 = 140.25.1.251/25

Host #124: 10001100.00011001.00000001.1 1111100 = 140.25.1.252/25

Host #125: 10001100.00011001.00000001.1 1111101 = 140.25.1.253/25

Host #126: 10001100.00011001.00000001.1 1111110 = 140.25.1.254/25 

Defining the Broadcast Address for Each Subnet

The broadcast address for Subnet #3 is the all 1s host address or: 

10001100.00011001.00000001.1 1111111 = 140.25.1.255 

The broadcast address for Subnet #3 is exactly one less than the base

address for Subnet #4 (140.25.2.0). 

Additional Practice with Subnetworks

Appendix C provides exercises using subnetting. 

U N D E R S TA N D I N G   I P   A D D R E S S I N G

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