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

A guided practice exercise covering Class C IP subnetting, walking through the calculation of subnet masks, network addresses, broadcast addresses, and usable host ranges across five networks using the 192.168.65.0 address space.

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About this video

This exercise builds subnetting proficiency through a structured Class C practice problem centered on the 192.168.65.0 address space. The scenario requires planning for five networks with host counts ranging from 2 to 22 per network, making it necessary to identify the largest requirement and design a subnet scheme that accommodates it. By analyzing both the number of networks and the number of hosts needed, the correct solution involves borrowing three bits from the host portion, producing a custom subnet mask of 255.255.255.224 and yielding eight total subnets with 30 usable host addresses each. Working through the binary math confirms that this configuration satisfies all network requirements with room to spare. The full walkthrough demonstrates how to derive every subnet's network address, broadcast address, and usable host range by applying binary logic and recognizing the increment pattern of 32. Rather than calculating each subnet individually from scratch, the approach identifies the repeating block size and uses subtraction to efficiently determine broadcast addresses and usable ranges across all eight subnets. This method reinforces both accuracy and speed, and the techniques applied here transfer directly to subnetting Class B and Class A addresses, which follow the same process at a larger numerical scale.

What you'll learn

What's covered

Class C Subnetting Practice

Aligned to

Cisco CCNA
1.6 Configure and verify IPv4 addressing and subnetting
CompTIA Network+
1.7 Given a scenario, use appropriate IPv4 network addressing
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

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.
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.
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.

Transcript

I added some grid lines to make it easier to track our work. I also formatted some of the information a little differently. You can see that we are working for five different networks, so there are five networks that we have. Here are the number of hosts that we have per network. We'll want to plan for the largest one to make sure that we can meet the needs of all of the networks. The IP address range is right here: 192.168.65.0. So that's what we're given to work with.

Working through it

As I mentioned before, we have five networks that we're planning for. We're planning anywhere from two hosts per network to 22 hosts per network, and we also have the 192.168.65 to work with.

First of all, what is our address class? This is a Class C, so our default subnet mask is 255.255.255.0.

Next is bits borrowed. We haven't figured that out yet. We need to plan for five networks, so this one wouldn't do it, this wouldn't do it, this would do it right there. We also need to plan for 22 hosts, so that wouldn't do it, that one and that one, but this would. So that's where we draw the line, right between those two. We don't really have any other options.

We can add in that we've borrowed three bits, so our custom subnet mask is 255.255.255 and right here is .224, so right at the .224. The total number of subnets that we have is eight — we have eight different networks that we are planning for. And usable hosts: here we have 30 usable hosts, so it's 30 usable hosts per network.

Listing the networks

Now we can actually figure out what those networks look like. So the first one here, we're going to just do 000, and then next is 001. This is where your binary counting comes into play here: 011, 100. Now, that's all we really need to plan for, because we don't have the extra networks needed. But because we have the space, and because this is a learning experience, I'm going to fill in the rest of this as well, so I'm going to figure out what all of our networks are going to be.

Next, what is the network address? For this first one, we would include all zeros in here to find the network address, which would be just .0. The next one after this would be all ones — excuse me, this would be the broadcast. So with all ones, that would be a .31, that's the broadcast there. So the usable range for this is .1 through .30. That's the usable address range right there.

I could do the same thing for this one. The network address would be all zeros, so that's a .32, because I just have a 1 in the 32 spot, so .32. The broadcast address would be all ones, so if it's all ones then I add all that together and that's a .63. So then the range here is anywhere from .33 through .62. That's the usable range.

A shortcut

One way that I could shortcut this is to start looking for patterns. I know that this is going to increment by 32, so I can go .32, I can do .64, I could do .96, I could do a .128, I could do a .160, do a .192 and .224. Once again, I'm just using this first part to figure all that out, because the rest of them I know are going to be all zero.

Once I do that, then I could just do the subtraction. I know that this range is going to end where this range picks up. So .95, .127, .159, .191, .223 and .255 is my last one. So there are all my broadcast addresses.

Then the usable range is just in between here, so it's .65 through .94, and .97 through .126, and .129 through .158, and .161 through .190, and .193 through .222, and finally .225 through .254.

I figured out all of the answers there. Make sure that you get this down before you progress on, because as we go to the Class B and the Class A, it's going to get a little bit more difficult just because you're working with bigger numbers. It's really not any more complicated than this, it's just that you're working with bigger numbers.

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