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Chapter 3: Installation
Figure 3-12. Subnet mask.
In this diagram, the subnet mask is 25 bits long, 255.255.255.128, and contains 126 members in the subnetted network. The
length of the network prefix equals the number of the bit with 1s in that subnet mask. This enables the switch to count the
number of IP addresses matched. The following table shows the results.
Table 3-3. Number of IP addresses matched.
Prefix Length No. of IP matched No. of Addessable 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
According to the scheme above, a subnet mask 255.255.255.0 will partition a network as class C. A maximum of 254 effective
nodes will exist in this sub-netted network, and it is considered a physical network in an autonomous network. The network IP
address might be 168.1.2.0.
Using the subnet mask, a bigger network can be cut into smaller pieces of network. If you want to have more than two
independent networks in a worknet, the switch must partition the network. In this case, the subnet mask must be applied.