Need technique for subnetting,CDIR and VLSM please!

Hi,
Would some kind soul help me out with a practical method to working out the subnetting elements for the 70-291 exam? I have a mental block with this stuff

, and cannot make any sense out of the resources on the net.
Does anyone have a good method ?

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Comments

fayo79

Easiest method would be to convert to binary the IPs to binary. And also use the 128, 64, 32, 16, 8, 4, 2, 1 table and just write it down on top.

chris.brown

say you have mask of 192.168.1.2/20
your mask has 20 bits. 255.255.240.0
2 to the power of the number of masked bits (4) cos thats how many come after the 255.255. -2 = number of subnets
so (2 to the power of 4) -2 = 14 subnets
do the same for unmasked bit to find the number of hosts per subnet.
(2 to the power of twelve -2) -2 = 4094 hosts per subnet.

jmc724

Theres an old book from exam cram called tcp/ip, it deals with all subnets and understanding them. It was one of those exams that were required for nt4 mcse.

You can find this book at a second hand book store or e*ay...

PawNtheSandman

chris.brown wrote:

say you have mask of 192.168.1.2/20
your mask has 20 bits. 255.255.240.0
2 to the power of the number of masked bits (4) cos thats how many come after the 255.255. -2 = number of subnets
so (2 to the power of 4) -2 = 14 subnets
do the same for unmasked bit to find the number of hosts per subnet.
(2 to the power of twelve -2) -2 = 4094 hosts per subnet.

Thanks, that explained it alot better than my books.

But once I do that, how do I determine the exact IP addresses to assign for the network?