In this diagram, you can see the subnet mask with 25-bit long, 255.255.255.128, contains 126 members in the sub-netted network. Another is that the length of network prefix equals the number of the bit with 1s in that subnet mask. With this, you can easily count the number of IP addresses matched. The following table shows the result.

Prefix LengthNo. of IP matchedNo. of Addressable IP

/32

 

1

 

-

 

 

 

/31

 

2

 

-

 

 

 

 

 

 

 

 

/30

 

4

 

2

 

 

 

 

 

 

 

 

/29

 

8

 

6

 

 

 

/28

 

16

 

14

 

 

 

/27

 

32

 

30

 

 

 

 

 

 

 

 

/26

 

64

 

62

 

 

 

 

 

 

 

 

/25

 

128

 

126

 

 

 

/24

 

256

 

254

 

 

 

 

 

 

 

 

/23

 

512

 

510

 

 

 

 

 

 

 

 

/22

 

1024

 

1022

 

 

 

 

 

 

 

 

/21

 

2048

 

2046

 

 

 

/20

 

4096

 

4094

 

 

 

/19

 

8192

 

8190

 

 

 

 

 

 

 

 

/18

 

16384

 

16382

 

 

 

 

 

 

 

 

/17

 

32768

 

32766

 

 

 

/16

 

65536

 

65534

 

 

 

 

 

Table 2-4

According to the scheme above, a subnet mask 255.255.255.0 will partition a network with the class C. It means there will have a maximum of 254 effective nodes existed in this sub-netted network and is considered a physical network in an autonomous network. So it owns a network IP address which may looks like 168.1.2.0.

With the subnet mask, a bigger network can be cut into small pieces of network. If we want to have more than two independent networks in a network, a partition to the network must be performed. In this case, subnet mask must be applied.

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KTI Networks KS-2262 user manual Prefix Length No. of IP matched No. of Addressable IP