Publication date: Nov., 2014
Revision A1
24
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 Length No. of IP matched No. 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 2-3
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 worknet, a partition to the network must be performed. In this
case, subnet mask must be applied.
For different network applications, the subnet mask may look like 255.255.255.240. This means it
is a small network accommodating a maximum of 15 nodes in the network.
25 bits
1 0000000
1 1111111
All 0s = 128.1.2.128
All 1s= 128.1.2.255
