Applied Subnetting in Enterprise Design
Analyze real-world network needs, create efficient subnets, assign IPs, and configure a working network in Packet Tracer.
You've joined ByteTech Solutions as a network technician. The network works — but it's inefficient. It uses a single Class C network and relies on a central legacy switch for all interdepartmental communication. Your job is to redesign it using subnetting to segment departments, improve performance, and enhance security.
Network Information
| Legacy network block | 192.168.0.1/24 |
|---|---|
| New network block | 192.168.100.0/24 |
| Current switch config | IP 192.168.100.2, DHCP server serving the full /24 |
| Router IP | 192.168.0.1 |
Department requirements
| Department | Device types | Approx. device count |
|---|---|---|
| IT | Desktops, servers, switches | 50 |
| HR | Desktops, printers | 25 |
| Sales | Laptops, phones | 15 |
| Guest | Short-term phones, tablets | 10 |
A real "Class C" address block (192.168.0.0/24) has nothing to do with how it's actually used today — classful addressing (Class A/B/C) was replaced by CIDR in the 1990s. ByteTech's legacy network is called out as "a single Class C" specifically because it highlights the original sin: one flat broadcast domain for every department, with no isolation between a guest tablet and an IT server. Subnetting — not a bigger address block — is the fix.
Quick Subnetting Review
For the full walkthrough, see the review page attached to this assignment in Canvas. Short version:
- Convert the subnet mask to binary.
- Count the host bits (the 0s in the mask).
- Usable hosts = 2n − 2 (subtract the network address and broadcast address).
- CIDR = 32 − host bits.
Plan Your Subnet Design
For each department, calculate the smallest subnet that fits its device count. Enter your values and check your work — the checker only tells you right or wrong, it won't calculate it for you.
| Department | Devices Needed | Host Bits (n) | Usable Hosts (2ⁿ−2) | CIDR (/__) | Subnet Mask |
|---|---|---|---|---|---|
| IT | 50 | ||||
| HR | 25 | ||||
| Sales | 15 | ||||
| Guest | 10 |
15 devices does not fit in a /28. A /28 gives 14 usable hosts — one short. Always check that 2n − 2 is greater than or equal to your device count, not just close to it.
Subnet Allocation Map
Start subnetting from 192.168.100.0, allocating largest blocks first so they land on clean boundaries. The first usable address in a subnet comes right after the subnet (network) address.
| Department | Subnet Address | CIDR | Usable Host Range | Broadcast Address |
|---|---|---|---|---|
| IT | ||||
| HR | ||||
| Sales | ||||
| Guest |
Redesign the Network
You'll now move into Packet Tracer to assign IP addresses to devices in each subnet. You'll remove the old switch and reconfigure the LAN router. Each department will use one router interface and two PC/endpoint devices for this model.
Prepare the network
- Power down and remove the old switch (
Switch0). - Run
no ip domain-lookupon the router so a mistyped command doesn't stall the CLI waiting on a DNS lookup. - Erase the current router configuration:
write erase reload
- Once the router reloads with a clean config, you're ready to reconfigure.
Check which router model your topology uses before wiring up four department links. PT's default ISR routers (1941/2901) only ship with Gi0/0 and Gi0/1 onboard — Gi1/0 through Gi4/0 require adding interface modules (HWIC/NM) in the device's physical config, or a completely different approach: trunk one physical link to a switch and use router-on-a-stick with a sub-interface per department (Gi0/1.10, Gi0/1.20, etc.). On real enterprise gear this exact tradeoff shows up too — you either buy a router with enough physical ports, or you subinterface a trunk. If your assignment specifies four physical Gigabit ports, confirm your router model actually has them before you start cabling.
Reconfigure the network
Reconnect each department switch to the router, activate the interface, and assign it an address. Run this block once per department (four times total), substituting your subnet's values:
interface giX/0 ip address 192.168.100.X 255.255.255.X no shutdown
Reserve the static addresses each department needs for servers/printers before configuring DHCP, and make sure to also exclude the router's own interface address:
ip dhcp excluded-address 192.168.100.X 192.168.100.X
It's easy to exclude the printer/server range and forget the gateway address itself. Cisco IOS does not automatically protect an interface's own IP from its DHCP pool — if you don't explicitly exclude it (e.g. the router's .1 on each subnet), the DHCP server can hand that address out to a PC, and you'll get an IP conflict with the default gateway. Exclude the gateway address on every subnet, not just the reserved server/printer ranges.
Then configure a DHCP pool per department:
ip dhcp pool [NAME] network 192.168.100.X 255.255.255.X default-router 192.168.100.X dns-server 8.8.8.8
| Department | Addresses to reserve (excluded from DHCP) |
|---|---|
| IT | 6 — servers and printers |
| HR | 3 — printers |
| Sales | 2 — printers |
| Guest | 0 — none |
Refresh IP addresses
DHCP reassignment can take a moment to propagate in Packet Tracer's simulation. Manually refresh each device's IP — either through the device's IP Configuration settings, or via ipconfig /release then ipconfig /renew at a PC's command prompt.
On real hardware, a DHCP client releasing and renewing can take anywhere from milliseconds to a few seconds depending on network conditions, and clients typically renew automatically well before their lease expires — you rarely force it by hand outside of troubleshooting. Packet Tracer's simulated DHCP exchange is simplified and can lag behind a config change, which is why a manual release/renew is standard practice in these labs even though it'd be an unusual step in production.
Device IP assignment record
Fill this in from your own Packet Tracer configuration once DHCP is working. There's no fixed "correct" answer here — it depends on where you put the gateway within each subnet — so this table isn't auto-checked.
| Department | Gateway IP | Endpoint 1 IP | Endpoint 2 IP |
|---|---|---|---|
| IT | |||
| HR | |||
| Sales | |||
| Guest |
This table isn't graded by the site — copy your final values into the worksheet you submit in Canvas.
Final Design Checklist
Document Your Topology
Take a screenshot of your new topology in Packet Tracer. Hover over the router to show its device info panel before capturing the image, so interface addressing is visible in the screenshot.
Reflection
In Canvas you'll be asked to answer the following. Keep them in mind as you work through the lab — you don't need to answer them here:
- What problems did the original design have?
- What was the hardest part of the subnetting process?
- What are the benefits of subnetting in real networks?
Grading
To receive credit for this lab, submit the following in Canvas:
- Completed tables from this worksheet
- Screenshot of your Packet Tracer network (with router interfaces visible)
- Reflection questions answered in Canvas
- Accurate subnet design with correct IP logic