In this Cisco CCNA training tutorial, we’re going to verify all of the subnetting information that we’ve covered so far by working through a subnetting practice question. Scroll down for the video and also text tutorials.
Subnetting Practice Questions Video Tutorial
Nicholas R White
Thanks again Neil for your fantastic CCNA course. I passed with no problems this last Monday and had the confidence to knock it out of the park.
The question is, what are the network address, the broadcast address and valid host addresses for the IP address of 126.96.36.199/26? In the second part of the question, what is the subnet mask in dotted-decimal notation?
Practice Question Answer
Let's look at how we are going to figure out the answer to the question. We're going to do the second part of the question first because it's more logical and easier to do it that way.
The second part of the question was, what is the subnet mask, /26, in dotted decimal? The way to do this, whenever you're working out a subnetting problem particularly at the start, is to write out the bit pattern at the top of a piece of paper.
Later on, you'll be able to do all these in your head, but when you're first learning, it's way easier to write it all out. So, take a piece of paper, start at the top, start at the right and we go 1, 2, 4, 8, 16, 32, 64, 128, and you can put a dot in. Proceed to the next octet, until you've drawn out the bit pattern for the four octets in your subnet mask.
Under your bit pattern at the top of the paper, write out 26 1s underneath starting from the left side. Then, you can put in the six 0s for the host portion of the address. Also, draw a line in where the line is for the subnet mask, and then we can just add these up.
The first octet is all ones, it's going to be 255. The second and third octets are also going to be 255. For the fourth octet, the ones are under 128 and 64. We add 128 and 64 together to give us 192. Therefore, /26 in dotted decimal notation is 255.255.255.192.
Let's look at what the second part of the question was. What is the network address, the broadcast address, and a valid host address for the IP address, 188.8.131.52/26?
Again, we use our piece of paper and we're going to write out the IP address now as well. We’ll write the bit pattern for 184.108.40.206. The network portion of the address is the first 26 bits, which is 198.22.45.
Then I just count whatever it is in the last octet’s first two bits. I've got a 1 for 128 and a 0 for the 64 so, that means 128. The network address is 220.127.116.11.
The long way is the logical way to do it. First, we write out the IP address on the subnet mask in binary notation and we put in the line where the subnet mask is. From that, we can figure out what the network address is which is 18.104.22.168.
Then we figure out what the broadcast addresses. That would be all of our host bits. So we add up 32, 16, 8, 4, 2, and 1. That would be equal to 63.
From the network portion, we found out that the network address was 22.214.171.124. 128 plus 63 is going to be 191. Therefore, the broadcast address is 126.96.36.199. Now, we've got the network address and the broadcast address.
The possible host addresses are going to be the addresses that lie between those two numbers. That would be 188.8.131.52 to 184.108.40.206.
We can take a little bit of a shortcut here and what we do is, look at where the line is. The line is after the 64, so I know that my subnets go up in multiples of 64. The first one is going to be 220.127.116.11, then 18.104.22.168, then 22.214.171.124, and so on.
The address that I'm interested in, is 126.96.36.199. The first subnet is zero, then 64, then 128. The next one would be 128 plus 64 is 192. 173 is less than 192, so it must be in the 128 network.
I know this is in the network 188.8.131.52. I then add on 64. I know to add on 64 because that's where the line is, and the next network address would be 192. If the next network address if 192, it must mean that the broadcast address for this subnet is one less than that. It's going to be 191.
There, I figured out my network address is 184.108.40.206. I figured out that my broadcast address is 220.127.116.11. The available host must be everything in between. That would be 18.104.22.168 to 22.214.171.124.
A final important point to tell you here is, notice that everything was done on where the subnet line is. This example is a /26 so that is in the last octet. So we don't actually need to worry about the first three octets. They are always going to be unchanged as 198.22.45 in our example.
You can see for some time, they're only writing out the octet that the subnetting is happening on. You don't have to write the whole thing out in full every time.
Where to Get More Subnetting Practice
If you are not sure about subnetting and you want some more practice, then there are some good resources listed below:
These are websites that have the same type of questions that you could see on the CCNA exam. Every time you refresh it, it will come up with a new question. It has variations on everything that’s subnetting related, so you should be confident that you can answer any of these questions now.
To check the answer, you can click and reveal the answer. It shows you the answer and then you can go on to the next question. If you're like me, you're not going to just learn this in one go and then have it down. You're probably going to want to practice it a little bit.
Don't spend hours on end practicing subnetting, that's no fun for anybody, but to get ready for the exam, you could just come on here and spend five or 10 minutes a day just working through a few problems.
If you do that for days or even weeks before the exam, you'll be fine when you get those subnetting questions. Another thing to tell you is, in the real world, people don't do subnetting in their head, typically, if that wasn't obvious already.
What we do is we use a subnet calculator. What you can do is you can go to Google and search for subnet calculator. What this is useful for is if you are doing subnetting in the real world, if you need to figure anything out.
Also, if you're doing exam practice and you want to check that you got the answer right, you can just come in here, plug in the numbers, and it will give you the answer.
IP Subnetting and Subnetting Examples: https://ipcisco.com/lesson/ip-subnetting-and-subnetting-examples/
Text by Libby Teofilo, Technical Writer at www.flackbox.com
With a mission to spread network awareness through writing, Libby consistently immerses herself into the unrelenting process of knowledge acquisition and dissemination. If not engrossed in technology, you might see her with a book in one hand and a coffee in the other.