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The question is:

Given the Network ID 41.149.210.0/24, subnet to provide 12 usable hosts per subnet. What is the new mask in CIDR notation (without the leading /)?

My question is, how... and elaborate! Cheers

4

You need 12 usable hosts, lets start from 1 and multiply by two each time.

  1. 1
  2. 2
  3. 4
  4. 8
  5. 16

Ok 16 is enough, even if we remove 2 hosts, we are left with 14, which satisfies requirement for 12.
And 16 is 5th number we found, so it is 5th smallest network.

Then we just count backward from smallest possible network, i.e. /32, and we get

  1. /32
  2. /31
  3. /30
  4. /29
  5. /28

Ok, it must be /28.

| improve this answer | |
  • Beautifully said. Thank-you very much! Cheers – user2581649 Nov 14 '13 at 10:01
  • So simple a server guy could understand! – John Kennedy Nov 14 '13 at 13:36

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