The Subnetting Game

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Quickly question about subnetting, more specifically the subnetting game on the Cisco website.

I have been doing the CCENT series by CBT. I am confident when following through Jeremy's examples but then using this process to subnet on the Cisco subnet game it says I'm doing the wrong mask.

For example in the game it will ask me to set up 2 subnets so I follow the CBT nugget processs (video 19)

2 networks needed:

128 64 32 16 8 4 2 1

0 0 0 0 0 0 1 0 = 2 bits borrowed

Then turn subnet mask into binary
255.255.255.0 = 11111111.11111111.11111111.00000000
New Mask=

11111111.11111111.11111111.11000000 > 128+64 = 192 so mask will be 255.255.255.192
Increment will be 64

So ranges should look like this:
192.168.1.0 - 63 (0 net 63 broadcast)
64-127 etc

However, if I try and enter this as correct on the Subnet game it will only allow me to put in a subnet mask of 128 which will give me two subnets.

Please please help - I'm obviously doing something wrong



EDDITTTTT!!!

Just decided to move on from video 19 after trying to work it out all morning!!!! Video 21 explains all

Need to -1 when counting networks or +1 for hosts !!! Lovely job. Subnetting = sorted, very very happy!

 

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I don't know which method they are teaching you but this is the bit where you went wrong (by most other methods).
If you borrow 1 bit you have 2 potential networks (borrowed bit set to 0 and borrowed bit set to 1).
You should start your counting at 2, not 1: 2,4,8,16,32,64,128,256...
The number of hosts is exactly the same, but you subtract 2 (for the network and broadcast address).

Example:
How many bits do you need to borrow to give 6 subnets?
The first number after 6 is 8. 2,4,8....3 bits.

How many host bits do you need for each subnet to have 28 hosts?
28 hosts+broadcast address+network address=30 different addresses.
2,4,8,16,32.....5 bits for the host portion

 

It would have been much better if you had included the actual question from the game. Without that crucial piece of info this is very difficult to answer. However, most mistakes with subnetting involve using the wrong formula in the wrong place.

Remember that
2n= # of subnets (where n equals the numer of bits borrowed)
and
2n-2= # valid hosts (with hosts we have 2 addresses we cannot use: broadcast and network/subnet IDs)