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TechKnowSurge Catalog Videos DEMO: VLSM Example C-2
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DEMO: VLSM Example C-2

A hands-on VLSM practice exercise working through an eight-network 192.168.20.0 scenario with varying host requirements, covering network addresses, usable host ranges, and broadcast addresses. Reinforces variable length subnet masking by applying the full subnetting process from start to finish.

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About this video

Variable length subnet masking allows a single IP address block to be divided into subnets of different sizes, each sized to match actual host requirements rather than a fixed allocation. This exercise puts that principle into practice using a 192.168.20.0 network split into eight segments ranging from 60 hosts down to just 2 hosts — a distribution that would be impossible to accommodate efficiently with standard subnetting. Subnets are assigned in descending order by host count, with each new subnet boundary placed immediately after the address space consumed by the previous one. Network addresses, broadcast addresses, and usable host ranges are derived for each segment by analyzing the binary structure of the address block and tracking which bit combinations have already been allocated. The process highlights how quickly address space is consumed and why working largest-to-smallest is essential for fitting all required networks into the available range. By the time the smallest subnets are reached, only a narrow slice of address space remains, and the exercise shows that the method still produces valid, non-overlapping network definitions for each segment. Completing this walkthrough builds fluency with the VLSM workflow — calculating boundaries in binary, converting to dotted-decimal, and verifying that no address ranges overlap — skills that are directly applicable to real-world network design and professional certification exams.

What you'll learn

What's covered

VLSM Practice Example

Aligned to

CompTIA Network+
1.7 Given a scenario, use appropriate IPv4 network addressing.
Cisco CCNA
1.6 Configure and verify IPv4 addressing and subnetting.
Cisco CCST Networking
2.2 Identify IPv4 addresses and subnet formats.
CompTIA A+ Core 1
2.6 Compare and contrast common network configuration concepts.

Key terms

Variable Length Subnet Mask
VLSM
A subnetting technique that allows a network administrator to divide an address space into subnets of different sizes by using different prefix lengths, allocating address space more efficiently than fixed-length subnetting. VLSM requires a classless routing protocol such as OSPF, EIGRP, or RIPv2 that carries prefix length information in routing updates.
Subnet
A logical subdivision of an IP network, used to organize and segment network traffic.
Subnet Mask
A 32-bit number that divides an IP address into network and host portions.
IP Address
A numerical label assigned to each device connected to a network that uses the Internet Protocol.
Network Address
The first address in an IP network range that identifies the network itself and cannot be assigned to a host. It is formed when all host bits are set to zero.
Broadcast Address
The last address in an IP subnet range, formed when all host bits are set to one, used to send a single packet to every device on that network simultaneously.
Usable Host Range
The set of IP addresses within a subnet that can actually be assigned to network devices, spanning from one address above the network address to one address below the broadcast address. For example, in the 192.168.1.0/24 network, the usable host range is 192.168.1.1 through 192.168.1.254.

Transcript

Let's do another example of VLSM, but this time I'm going to allow you to do the work, and then you can check the work, and then we'll come together at the end and I'll step you through the process in case you have any questions.

Here's the example that we're going to use. It's still a 192.168.20 network, but it's broken down into eight different networks here. It also has a lot of different hosts per each one. If we were just to do standard subnetting with this, we wouldn't be able to make it all work because of the differing needs here.

So what you can do now is go through the process of figuring out all the networks with this. Figure out all of the network addresses, the usable hosts and the broadcast address, write it all down, and then we'll go over the answers.

Checking the answers together

Here are the answers. Go ahead and check your answers and see how close you got. All right, should we do this together?

The first one that we need is a network that has 60 hosts to it. So what we're going to do is find the one that allows us to do 60 hosts, right there. This is where we draw the line for that first one, and we will write in 00, since that's the start of this. So the network address would be .0, because the rest of these for the network address would be zero.

I'm probably just going to figure out all the network addresses and go from there. So I've got this 55 in here, which looks like the same one, so I'm going to draw the line at the same point for that one. I can't use 00 — that's been taken up with that whole range from the network before it. So now I'm going to do 01, the next number that I can use in this range. So same thing: we've got the network address of .64.

Next up we've got this network of 53 right here. So what I'm going to do is find which one works, which is the same one again, so I'm going to draw it down. I can't use the 01 now, that whole range has been used up, but I can use a 10. And then if I were to have zeros in for the rest of these, then that would be .128.

Next up is 29 here. So for 29 I can actually use this one right here, so for this one I could draw the line right there. Which is good, because I'm starting to run out of address space — I've already gone to the 191. So it's good, because otherwise we would use up all of our IP addresses here. Now, I've already used a 10 and a 01 and a 00 for the first two bits, so the only thing I have left here is a 11. So it's got to be 11, and so we'll do 110. So that is 128 plus 64 is 192, so we'll put 192 in there for the network address.

The next is 14. So here is 14 right here. I can draw the line for this one right there, so let me make that a little bit darker. I've already used up the 110 here, so this needs to be 111 — these just start out with 111. So that is where we're starting out at. I can put zero there, and if I were to put 0 for the rest of these, I could add up 128 plus 64 plus 32, that's 224. So there's the network address for that.

And then I have just this little two here. So the two, I could go right here with it, so I'm going to draw the line right there for that one. And the rest of these are two as well, so I'm just going to draw the line all the way down for the rest of these. I've already used up the 1110 here, so the next one has to be 1111. That's the only thing that I've got left. So I could do a 00 on this first one, I could do a 01 on the next one, and a 10 on the next one after that. I'll just drop these down here. So I could actually have room for one more address down below, one more network. So if I needed one more network that just had two hosts on it, I could make that happen.

All right, so what are these? 128 plus 64 plus 32 plus 16 is 240, so we'll write in 240 there. 240 plus 4 is 244, and 240 plus 8 is 248. All right, those are all my networks.

Broadcast addresses and ranges

For the broadcast address, it's just going to be if these were all ones here, 1111111. So I could either calculate it that way, or I could take the next network and subtract one, so .63. Either way, that's the answer that I'm going to get.

So .127. The next one is 191. The next one is .223. The next one is .239. The next one is 243, 247, and then this one is 252. And I can either look at the chart for this — actually it's 251, the next network is 252. So I could manually calculate that out by putting ones in there just like that.

So then, what is the ranges? I come back in here, and the first one is the address right after the network address, going to the one right below the broadcast address. So there's the range, and then I would do this for each one to fill in the rest of it. So I'm not going to bore you with filling this all out. You saw the answers and you know what the answers are.

So that's how you do this variable length subnet masking.

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