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 |
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/32 | 1 | - |
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/31 | 2 | - |
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/30 | 4 | 2 |
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/29 | 8 | 6 |
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/28 | 16 | 14 |
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/27 | 32 | 30 |
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/26 | 64 | 62 |
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|
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/25 | 128 | 126 |
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/24 | 256 | 254 |
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/23 | 512 | 510 |
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|
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/22 | 1024 | 1022 |
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/21 | 2048 | 2046 |
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|
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/20 | 4096 | 4094 |
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/19 | 8192 | 8190 |
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/18 | 16384 | 16382 |
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|
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/17 | 32768 | 32766 |
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|
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/16 | 65536 | 65534 |
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|
|
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
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.
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