Master IP Subnetting Forever

I agree with Chris Bryant at The Bryant Advantage. You should know how to subnet using binary. Knowing that, I went through his binary conversion and subnetting course, and learned it well. Practiced every day at subnettingquestions.com, until I no longer made silly errors, and it made sense to me.

But as exam day neared, I worried that I would be too slow with all of these binary conversions. I also found that when I hurried my conversions, the silly errors returned.   In my studies on the Cisco Learning Network, I saw people referring to an "increment of 16", or an "increment of 32". What does that mean? I found out here: Master IP Subnetting Forever. The "magic box" is a huge timesaver.

This document is truly a lifesaver, along with the "thumb rule". I don't remember where I learned it, but when it comes to the "power of two", the thumb rule is great. When trying to figure out "2 to the 5th power", stick your thumb out. That's two, or "2 to the 1st", now start doubling the number, extending a finger each time. 4, 8, 16, 32.  When you get to your fifth finger, you are at 32. "2 to the 5th" is 32. Now, if you are counting available host addresses, subtract 2. Five host bits gives us 30 hosts per network.

Just keep counting, and keep doubling. "2 to the 10th" is 1024, or 1022 hosts. Easy stuff. But again, learn how to do it in binary first. You should always know how to do it at the fundamental level, so when you forget the "trick" or the "magic box" you can fall back on the basics.