Subnetting – Hosts Per Subnet

subnetting

The Joys of Subnetting Knowledge:

Remember, while practicing just how fast you can ace subnetting questions in the certification environment is always worthwhile and fun, you do want to make sure you understand exactly why you are going through the exercise to begin with. You also want to be sure you understand how subnetting fundamentally works. This is often referred to as subnetting “longhand”. This is why a course like the CBT Nuggets IPv4 Subnetting – The Ultimate Guide is so critical.

ICND1 Sample Question:

You have run the ipconfig command and discovered your IP address and mask are 192.168.20.102 and 255.255.255.224. How many hosts are permitted on your subnet?

Step 1: I reference the Powers of Two chart I created on my scratch paper when I encountered the first question. Adding 128 + 64 + 32 = 224. There are 3 bits used for subnetting and that leaves 5 bits for hosts.

2^7=128  |  2^6=64  |  2^5=32  |  2^4=16  |  2^3=8  |  2^2-=4 | 2  ^1=2  |  2^0=1

Step 2: The equation for the number of hosts per subnet is 2^h – 2 where h is the number of host bits. From the chart I see that 2^5  = 32. 32-2 = 30 hosts per subnet! Too easy!

As always, let us know in the comments if you have a quicker approach.

4 thoughts on “Subnetting – Hosts Per Subnet

  1. First time visitor after purchasing your Net+ Cert Guide N10-007. (I have the N10-006 version as well. Both versions are great.) On this webpage, you have a typo in the very first sentence in the paragraph under header: The Joys of Subnetting Knowledge. being = begin. Please fix then delete my nit-picky comment. 🙂

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