Subnetting, the extremely easy way, no more memorizing formulas.
I looked for a bit and haven't seen anyone talk about this, so i thought i would make a post about it. I'm sure this method is around but i haven't seen it anywhere, i think the way that JITL explains it is a bit overwhelming, but that's just me.
By and far the easiest way to subnet is by simply calculating the network address and then the broadcast address, for me at least. Of course you need to understand how to convert the address into binary, and host bits/network bits, but that is easy.
Example problem, and how I work through this in my head.
89 .29 .171 .212 /20
Okay so, first 2 octets can be ignored, because this is a /20 mask. I only need to convert 171 to binary, because the network address ends within this octet.
I am only going to show my full work on how to convert an address to binary once.
.171 binary conversion
171-128 = 43 = 1
43 - 64 = -X = 0
43 - 32 = 11 = 1
11 - 16 = -X = 0
11 - 8 = 3 = 1
3 - 4 = -X = 0
3 - 2 = 1 = 1
1 - 1 = 0 = 1
Now i am going to bold (on paper i underline you cant do that on reddit) which portion of 10101011 are the host bits, and calculate the network address.
10101011
Network address = all host bits set to 0
Network address binary = 10100000.00000000
To calculate the network address, i am simply adding 128+32, since the 1s in those octets equal those numbers.
Full network address = 89 .29 .160 .0
To find the next host i simply add a 1 to the network address.
First host address = 89 .29 .160 .1
Now i am going to calculate the broadcast address, which i know is all host bits set to 1
First, write it out in binary
01011001 . 00011101 . 10101111 . 11111111
Broadcast address = 89 .29 .175 .255
Now to calculate last host and next subnet, all you do is simply add and subtract from the broadcast address.
Last host (subtract 1) = 89 .29 .175 .254
Next subnet (add 1) = 89 .29 .176 .0
Hope this helps, im writing this to help anyone struggling and also to help myself memorize the topic, i read somewhere online that teaching others is a great way to memorize things.