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Finding The Number Of Networks (subnetting Questions)


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#1 gardabble

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Posted 12 March 2010 - 08:26 AM

I got a question.  In an job interview I had a question something like this:

You have a network address 192.168.0.0/27.  Calculate the number of networks (subnets)?

My answer is 8.  But I see proprofs tutorial subtract 2 for that to be 6.   So I am a little lost.  I seen books finding that subnet is 2^(count the # of network bits off the subnetmask).  For  finding the host its 2^(count the number 0's in the subnetmask octet - 2 for broadcast address and start of network)  Can someone clear the confusion?

#2 s7davis

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Posted 14 March 2010 - 07:40 AM

QUOTE (gardabble @ Mar 12 2010, 09:26 AM) <{POST_SNAPBACK}>
You have a network address 192.168.0.0/27.  Calculate the number of networks (subnets)?

My answer is 8.  But I see proprofs tutorial subtract 2 for that to be 6.   So I am a little lost.  I seen books finding that subnet is 2^(count the # of network bits off the subnetmask).  For  finding the host its 2^(count the number 0's in the subnetmask octet - 2 for broadcast address and start of network)  Can someone clear the confusion?

If you look at this question it is asking for the network bits so that will be the "1" on the binary code. The example you gave the code will look like this for the subnet.

11111111.11111111.11111111.11100000

Now after looking at this you notice you have 3 network bits and 5 host bits. Remember Networks are represented by the "1" and the host bits are represented by the "0". Now you want to calculate the number of newtworks you can have so it will be 2^3 I believe - 2. The minus 2 is because the first and last addresses are private and cannont be used. ONe is broadcast and the other I cannot remember.

So the answer will = 8. But then you have to minus - 2 for the two private addresses that cannot be used then you will get the toatal answer of 6.
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#3 gardabble

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Posted 16 March 2010 - 06:48 AM

I was watching a video on Train Signal on subnetting.  Found out something:

If you are using Rip version1 or the running config has no ip subnet-zero in it.  The formula to find the number of # of subnets= (2^subnet bits) -2. (In the 640-801 exam its the -2)

Otherwise its 2^subnet bits





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