The way I subnet

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The way I subnet: Takes around 30 seconds (if that) - with practice!

I have seen some stupid subnetting questions and thought I'd offer they way I do it to try and help.

Before you try and learn how to subnet you need to learn binary and the different classes of addresses.

Forget magic numbers and special tables, if you know binary it's easy, trust me.

Assumming the ip subnet zero command is in use, we will find the network address, broadbast address and address range.

191.16.97.150 with a mask of 255.255.255.192


Prefix notion:255.255.255.192 = /26


In the mask you always ignore the 255 and the 0 part so we use the 192 part( 4th octet )in the mask and the address.

192 in binary is
128 64 32 16 8 4 2 1
1 1 0 0 0 0 0 0


What ever the last one is in the mask 64 in this case, this is the number the subnet go up by:

Network number: 0 range: 0-62 BC Address: 63
Network number: 64 range: 65-126 BC Address: 127
Network number 128 range: 129-190 BC Address: 191
Network number 192 range: 193-254 BC Address: 255
Network number 256 (not valid as greater than 255)


Therefore as 192 in the mask is the 4th octet we use the 4th octet in the address: 150

From the above find what number is below 150, 150 is between 128 and 192 therefore:

191.16.97.150 /26

Network number 191.16.97.128 /26
range: 191.16.97.129 - 191.16.97.190
Broadcast Address: 191.16.97.191

After a bit practice as soon as you see the mask, you know the multiples of the subnets.
They can only be 128, 64, 32, 16, 8, 4, 2 or 1.. Look familiar don't they.

 

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Good post, thanks for sharing.

I'm going to start on my CCNA as soon as I get some of the lower level certs out of the way.