IP Subnetting

I am trying to refresh my subnetting knowledge. I watched TMC Heath Adams The Cyber Mentor’s video as part of his PNPT Live training this week. Then I watched Professor Messer’s Seven Second Subnetting on YouTube. Then… I went back to CBT Nugget Keith Barker’s Subnet Saturday video series on YouTube (specifically #6: The Finger Game and #8: VLSM). They all were good in their own way. However, I prefer Keith Barker’s method of subnetting more.
I did a little summary below for when given an IP address range in CIDR format, how to find the network ID, first available host, last available host and the broadcast address.
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192.168.0.0/23 — it concerns the third octet.
specifically, the 7 most significant bits of the 3rd octet (network bits).
128 192 224 240 248 252 [254] 255
subnet mask is 255 255.254.0
the host bits concerns the 1+8 = 9 least significant bits spanning the 3rd and 4th octets (respectively).
so, 2⁹ — 2 = 512 -2 = 510 available host addresses
the network address is 192.168.0.0
first host: 192.168.0.1
the network address for the next available network is:
this concerns the 3rd octet.
we have 1 host bit in the 3rd octet -> 2¹ = 2 → this is our block size.
and then, 192.168.2.0 (we added 2 to the 3rd octet)
so actually, 192.168.2.0 is the answer
and therefore, broadcast address for the current network is: 192.168.1.255
last host of the current network is: 192.168.1.254
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It does not end there — when it comes to VLSM subnetting, I have a couple of photos of whiteboard class notes showing how WelTec’s Lecturer Drew Duncan taught us to do VLSM subnetting. He put the process down into a little exercise on the whiteboard and…. it is the best yet in my opinion!