Signamax
™
065-7921PoE 12-Port 10/100/1000BaseT/TX Web Smart PoE Switch
20
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.
