Another Powerful Method for Subnetting

June 17, 2016 | Views: 11765

Begin Learning Cyber Security for FREE Now!

FREE REGISTRATIONAlready a Member Login Here

Here’s something that I learned from my CISCO class that makes things a lot easier.

You’re given an IP range of 192.168.0.0 and must create a domain that has five subnets – pockets of devices on the network that are separate from each other so that no one can interfere with another departments data or devices. You know the first part, five domains, now you’ll need to know how many host are going to be in each domain. They are:

Host A (Faculty) – 50 hosts (plus 1 for fast Ethernet Interface)

Host B (Students) – 100 hosts (plus 1 for fast Ethernet Interface)

Host C (Staff) – 26 hosts (plus 1 for fast Ethernet Interface)

WAN1 – Router A serial connection to Router C serial (2 hosts)

WAN2 – Router B serial connection to Router C serial (2 hosts)

 

That’s the easy part. Now, let’s set up a chart, which you should memorize for the exam:

Bits 128 64 32 16 8 4 2 1
CIDR /25 /26 /27 /28 /29 /30 /31 /32
Subnet Mask 128 192 224 240 248 252 254 255
Hosts 126 62 30 14 6 2

If you can memorize the above chart, then you should be able to ace the section on subnetting. When you go into the exam, sit down and do a brain dump. This is one of the first things that you’ll want to write down prior to logging onto the computer to begin your exam.

Now that you have that written down, you’ll come to the question at hand. How do you go about breaking up the IP address given you into five different domains? You’ll need to create another chart to assist you with this; there are some clues when you’re doing this.

Here’s the next chart:

Useable Host Network 1st Address Last Address Broadcast Address Subnet Mask
100
50
26
2
2

Have you noticed something? I’ve inputted, from highest to lowest, the number of hosts that we’ll need to create our network with the requested subnets. From here on, I’ll be going one line at a time, so it’ll make it easy to follow.

The first thing that you’ll input is the IP address that you were given, 192.168.0.0:

Useable Host Network 1st Address Last Address Broadcast Address Subnet Mask
100 192.168.0.0

 

Now, put in the 1st address that you will use:

Useable Host Network 1st Address Last Address Broadcast Address Subnet Mask
100 192.168.0.0 192.168.0.1

 

Notice, you have 100 hosts to fulfill, but, if you look at the chart that was first created, there is no 100 address. You cannot go down, but you can go up, so you go to the column of 126 hosts and put that to the 1st address.

Useable Host Network 1st Address Last Address Broadcast Address Subnet Mask
100 192.168.0.0 192.168.0.1 192.168.0.126

 

Of course, your broadcast address only goes up one bit, so input that:

Useable Host Network 1st Address Last Address Broadcast Address Subnet Mask
100 192.168.0.0 192.168.0.1 192.168.0.126 192.168.0.127

 

Here’s the fun part: you have a need of 100 hosts, but, you chose 126, what do you think would be the subnet mask? Look at the chart, it is right there:

Useable Host Network 1st Address Last Address Broadcast Address Subnet Mask
100 192.168.0.0 192.168.0.1 192.168.0.126 192.168.0.127 255.255.255.128

 

Looks simple, doesn’t it? Now, don’t get too confident. Let’s fill in the rest of the address and see if you notice something that will help you:

Useable Host Network 1st Address Last Address Broadcast Address Subnet Mask
100 192.168.0.0 192.168.0.1 192.168.0.126 192.168.0.127 255.255.255.128
50 192.168.0.128 192.168.0.129 192.168.0.190 192.168.0.191 255.255.255.192
26 192.168.0.192 192.168.0.193 192.168.0.222 192.168.0.223 255.255.255.224
2 192.168.0.224 192.168.0.225 192.168.0.226 192.168.0.227 255.255.255.252
2 192.168.0.228 192.168.0.229 192.168.0.230 192.168.0.231 255.255.255.252

 

You’ve now filled in the complete graph of the breakdown of your IP address. Did you notice a couple of things? This will help you to check yourself if you’re doing it properly. Look close. The Network and last address is always an even number, the first address and broadcast address is always odd. Also, the IP address that follows the broadcast address is just the next IP address.

These little bits of clues will help you in creating subnets for your domain. Once I saw the pattern, I was never wrong again in class.

I hope that I was able to explain it so you could follow along. I’ve passed on the tools that I’ve found helpful and hope that you’ll also find them just as useful.

Save

Save

Save

Save

Save

Share with Friends
FacebookTwitterLinkedInEmail
Use Cybytes and
Tip the Author!
Join
Share with Friends
FacebookTwitterLinkedInEmail
Ready to share your knowledge and expertise?
21 Comments
  1. The concept is great, just too cluttered when taught. Thks!

  2. Any tricks for class A and B?

Page 4 of 4«1234
Comment on This

You must be logged in to post a comment.

Our Revolution

We believe Cyber Security training should be free, for everyone, FOREVER. Everyone, everywhere, deserves the OPPORTUNITY to learn, begin and grow a career in this fascinating field. Therefore, Cybrary is a free community where people, companies and training come together to give everyone the ability to collaborate in an open source way that is revolutionizing the cyber security educational experience.

Cybrary On The Go

Get the Cybrary app for Android for online and offline viewing of our lessons.

Get it on Google Play
 

Support Cybrary

Donate Here to Get This Month's Donor Badge

 
Skip to toolbar

We recommend always using caution when following any link

Are you sure you want to continue?

Continue
Cancel