Networking Concepts

Subnetworks

Table 2-1

Valid Addresses of Example Subnetwork

 

 

 

 

 

 

 

 

Subnet

Address of

Decimal Value

Possible Node

Decimal Value of

 

 

Subnetwork in

of Subnetwork

Address on

Rightmost Byte

 

 

Binary

 

Subnetwork

 

 

 

 

 

 

 

 

1

001 (00000)

32

00001–11110

33–62

 

 

 

 

 

 

 

2

010 (00000)

64

00001–11110

65–94

 

 

 

 

 

 

 

3

011 (00000)

96

00001–11110

97–126

 

 

 

 

 

 

 

4

100 (00000)

128

00001–11110

129–158

 

 

 

 

 

 

 

5

101 (00000)

160

00001–11110

161–190

 

 

 

 

 

 

 

6

110 (00000)

192

00001–11110

193–222

 

 

 

 

 

 

By looking at the binary values of two IP addresses, it is easy to tell if nodes belong to the same subnet. If they do, all the bits that make up the subnet mask will be the same between IP addresses in the subnet.

Take, for example, two IP addresses (in decimal and in binary) of subnet number 1 from Table 2-1:

192.6.12.411100 0000 0000 0110 0000 1100 0010 1001

192.6.12.551100 0000 0000 0110 0000 1100 0011 0111

The subnet mask has already been defined as:

255.255.255 224 1111 1111 1111 1111 1111 1111 1110 0000

Because the mask has all bits except the five rightmost bits set to 1, all bits except the five rightmost bits must match between nodes on the same subnet. Because the two example IP addresses from subnet 1 do match except for their five rightmost bits, they belong to the same subnet.

NOTE

Subnet addressing can be used in internetworks (networks with

 

gateways).

30

Chapter 2