Apr 29, 2011

Subneting a class C address *** THE FAST WAY! ***

You need to do is answer five simple questions:
  1. How many subnets does the chosen subnet mask produce?
  2. How many valid hosts per subnet are available?
  3. What are the valid subnets?
  4. what's the broad cast address of each subnet?
  5. what are the valid hosts in each subnet?
well ...

1:  2^x = Number of subnets
X is the number of masked bits, or the 1s.

FOR EXAM: in 11000000 the number of 1s gives us 2^2 subnets.
- in this example, there are 4 subnets.

2:  2^y - 2 = Number of  hosts per subnet.
Y is the number of unmasked bits, or the 0s.

FOR EXAM: in 11000000 the number of 0s gives us 2^6 - 2 hosts.
- in this example, there are 62 hosts per subnet address & the broad cast address,  which are NOT valid hosts.

3:  256-subnet mask  = block size, or increment number.
FOR EXAM: would be 256 - 192 = 64
the block size of 192 mask is always 64.   
bin:  11000000     dec: 128+64+0+0+0+0+0+0=192
star counting at zero in block of 64 untill you rich the subnetmask.
value & these are your sub-nets.  0, 64, 128, 192.   Easy, huh?   0, (+64) 64, (+64) 128, (+64) 192

4:  since we ciunted our subnets in the last section as 0, 64, 128 & 192. the broad cast address is always the number right befor the next subnet!

FOR EXAM: the subnet has a broadcast address of 127 because the next subnet is 128.
and so on!! remember, the broad cast address of the last subnet is always 255.

5:  valid hosts are the number between the subnet, all 0s & all 1s.
FOREXAM: if 64 is the subnet number & 127 is the boardcast address then 65 - 126 is the valid host range. it's always the numbers between the subnet address & the broadcast address.

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