Build a Two-Department Office Network

Build two routed office LANs and troubleshoot IPv4 subnetting in Packet Tracer.

Introduction

30 Second Summary

Most office networks feel invisible until one team can reach its own computers but cannot reach another department. That moment raises a useful question about where one network ends.

In this project, you will build a two-department virtual office in Cisco Packet Tracer. You will watch Ethernet switching reach its limit before IPv4 routing reconnects the departments.

What You'll Build

You will watch test traffic cross two virtual departments after R1 turns a blocked network boundary into a working route.

By the end of this project, you'll have:

  • Connectivity proof: Run ping inside each department. See the cross-department test fail before R1 is configured. Repeat it after routing is active to see replies.
  • A labeled CIDR map: Read the network address, usable host range, broadcast address, subnet mask, and gateway for both /25 networks.
  • Forwarding evidence: Inspect dynamic switch MAC entries. View both connected router routes. Follow the packet path with tracert in your saved two-department-office.pkt lab.
  • Secret Mission: Give one PC the wrong subnet mask. Diagnose why local traffic works while remote traffic fails. Restore the correct /25 mask.

Are there any prerequisites?

You need a Windows 10 or Windows 11 PC with at least 4 GB RAM plus internet access. No previous networking experience is required because Step 1 covers the free Cisco Networking Academy account and simulator setup.

Before We Start

Before you start building, take a moment to connect this office network to your own goals. Your reason will give the switching, routing, and CIDR decisions a clear purpose as the two departments come together.

Set Up Cisco Packet Tracer

Your project purpose is clear. Now you need a simulator that turns networking ideas into visible behavior.

Cisco Packet Tracer gives you a virtual Logical workspace for building the office network. Access starts with a free Cisco Networking Academy account.

In this step, you will create that account. You will install the simulator on Windows.

You will authenticate Packet Tracer with your new credentials. The finished setup opens to a blank Logical workspace.

In this step, get ready to:
  • Activate a free Cisco Networking Academy account.
  • Install Cisco Packet Tracer on Windows.
  • Open an authenticated blank Logical workspace.
Create your NetAcad account

Your NetAcad account becomes your Packet Tracer sign-in. Credential screens can feel sensitive, so the setup begins from Cisco's official signup page.

  • Open the official NetAcad signup page in your web browser.
  • Complete the account form with your own details.
  • Submit the account form.
  • Complete any email verification that NetAcad requests.
  • Return to NetAcad in your web browser.
  • Sign in with your new credentials.

You should reach an authenticated NetAcad page with no email verification task waiting. That clears the account hurdle that controls access to Packet Tracer.

Install Cisco Packet Tracer

The NetAcad lab downloads page provides the Windows installer. The installer copies Packet Tracer onto your computer before offering to launch it.

You should see the installer listed as a completed download in your browser.

The installer has several similar pages, so losing your place is easy. Windows may also show a permission request when the installer starts.

  • Run the downloaded installer from your browser's downloads list.
  • Approve the Windows permission request if it appears.
  • Select I accept the agreement on the License Agreement page.
  • Continue from Select Destination Location without changing the default folder unless you need another location.

The next pages control the Start menu location and optional installer tasks. Their default selections work for this project.

  • Continue through Select Start Menu Folder without changing its default selection.
  • Continue through Select Additional Tasks without changing its default selection.
  • Select Install in the Ready to Install window.

You should see the installation progress complete before the final installer page opens.

  • Leave Launch Cisco Packet Tracer selected.
  • Choose Finish.

Cisco Packet Tracer should start and display its first-launch prompt.

Installer not opening?

  • Confirm that your browser finished downloading the Windows installer.
  • Download a fresh installer from the NetAcad lab downloads page if the setup window never opens.

Help me troubleshoot a Cisco Packet Tracer installation that does not open or finish on Windows. Review Cisco's official installation guide for the documented Windows flow.

Authenticate and check the workspace

Packet Tracer authenticates through your NetAcad account before opening the workspace. Declining multi-user startup keeps this project in the standard local workspace.

  • Choose No when Packet Tracer asks Would you like to run multi-user when the application starts?.
  • Select LOGIN on the Packet Tracer sign-in screen.
  • Complete the browser authentication with your NetAcad credentials.
  • Wait until the browser displays You have successfully logged in to Cisco Packet Tracer. You may close this tab.

Before you return to Packet Tracer, which screen do you expect to see after authentication?

  • Return to Cisco Packet Tracer from the Windows taskbar.

You should see a blank Logical workspace with no authentication prompt remaining. Multi-user startup mode should also remain disabled.

You have cleared the full setup path. Packet Tracer is now authenticated and ready to hold your office network.

Login prompt still showing?

  • Confirm that you completed any email verification requested by NetAcad.
  • Return to the browser tab to confirm that the successful login message is visible.
  • Select LOGIN again if the browser authentication did not finish.

Help me troubleshoot why Cisco Packet Tracer still asks me to log in after NetAcad browser authentication.

Your networking workspace is ready. Next, you will turn that blank canvas into two connected department LANs.

Build Two Switched LANs

Your Cisco Packet Tracer workspace is ready. The blank Logical workspace is where your office network takes shape.

This step lets you compare traffic inside one LAN with traffic aimed at a second network. The result exposes the boundary between switching and routing.

In this step, get ready to:
  • Build the seven-device office topology.
  • Assign static IPv4 settings to four PCs.
  • Compare local connectivity with cross-department connectivity.
Place and name the office devices

The router sits between two department switches. Each switch serves two PCs inside its department.

  • Select Network Devices in the bottom-left device panel.
  • Select Routers in the subcategory row.
  • Select the Cisco 4321 router model.
  • Place the Cisco 4321 near the center of the Logical workspace.
  • Select Switches in the subcategory row.
  • Select the Cisco 2960 switch model.
  • Place one Cisco 2960 to the left of the router.
  • Place another Cisco 2960 to the right of the router.

How should the topology look?

The left switch represents the Administration department. The right switch represents the Engineering department.

R1 occupies the boundary between them. This layout makes the two LANs easy to compare.

  • Select End Devices in the bottom-left device panel.
  • Select the PC device.
  • Place two PCs below the left switch.
  • Place two PCs below the right switch.

You should now see one router between two switches. Four PCs should sit below the switches.

The display-name target is small. Packet Tracer may open the device window if you hit the icon.

  • Click the display name below the router icon.
  • Replace the router display name with R1.
  • Rename the left switch Admin-SW.
  • Rename the right switch Engineering-SW.
  • Rename the upper-left PC Admin-PC1.
  • Rename the lower-left PC Admin-PC2.
  • Rename the upper-right PC Engineering-PC1.
  • Rename the lower-right PC Engineering-PC2.

You should see all seven project names beneath their device icons. The two departments are now visually separated.

Having trouble renaming a device?

Click the existing text beneath the device instead of the device icon. Close the device window if it opens.

You can also select the device's Config tab. Enter the required name in the Display Name box.

Check spelling carefully because later instructions use these exact names. Help me fix a Packet Tracer device name that I cannot edit.

Cable the two department LANs

Copper Straight-Through cables carry Ethernet traffic between different device types. Each PC connects to its department switch before either LAN reaches R1.

  • Select Connections in the bottom-left device panel.
  • Select Copper Straight-Through from the cable choices.
  • Connect Admin-PC1 FastEthernet0 to Admin-SW FastEthernet0/6.
  • Connect Admin-PC2 FastEthernet0 to Admin-SW FastEthernet0/18.
  • Connect Engineering-PC1 FastEthernet0 to Engineering-SW FastEthernet0/6.
  • Connect Engineering-PC2 FastEthernet0 to Engineering-SW FastEthernet0/18.
  • Connect R1 GigabitEthernet0/0/0 to Admin-SW FastEthernet0/1.
  • Connect R1 GigabitEthernet0/0/1 to Engineering-SW FastEthernet0/1.

You should see six cables across the topology. Each cable should end on the specified interface.

Why use straight-through cables?

A Copper Straight-Through cable connects different types of Ethernet devices. Your PC-to-switch links follow this pattern.

Your router-to-switch links use the same cable type. The selected interfaces determine where each frame enters the topology.

Does a cable use the wrong port?

Delete only the incorrect cable. Select Copper Straight-Through again before reconnecting the two devices.

Check every full interface name in the port menu. Help me correct a Packet Tracer cable that uses the wrong interfaces.

Address the PCs and test both paths

The subnet mask tells each PC which destinations belong to its local network. A default gateway stores the next destination for traffic that must leave that network.

  • Click Admin-PC1 in the Logical workspace.
  • Click the Desktop tab.
  • Click IP Configuration.
  • Select Static.
  • Configure Admin-PC1 with these values:
  • Close the Admin-PC1 window.

Admin-PC1 now has its static address. Its gateway points toward R1's Administration interface.

  • Click Admin-PC2 in the Logical workspace.
  • Click the Desktop tab.
  • Click IP Configuration.
  • Select Static.
  • Configure Admin-PC2 with these values:
  • Close the Admin-PC2 window.
  • Return to Admin-PC1.
  • Click the Desktop tab.
  • Click Command Prompt.
  • Test the Administration LAN by running this command:
ping 172.16.20.11

What does this command test?

The command sends requests from Admin-PC1 to Admin-PC2. Replies prove that both PCs can exchange traffic through Admin-SW.

You should see replies from 172.16.20.11. Your Administration LAN is now carrying local traffic.

No replies from Admin-PC2?

Check that both Administration PCs use 255.255.255.128. Confirm that their addresses end in .10 and .11.

Verify that the PC cables reach FastEthernet0/6 and FastEthernet0/18 on Admin-SW. Help me troubleshoot the failed local ping between my Administration PCs.

  • Click Engineering-PC1 in the Logical workspace.
  • Click the Desktop tab.
  • Click IP Configuration.
  • Select Static.
  • Configure Engineering-PC1 with these values:
  • Close the Engineering-PC1 window.

Engineering-PC1 now has its static address. Its gateway points toward R1's Engineering interface.

  • Click Engineering-PC2 in the Logical workspace.
  • Click the Desktop tab.
  • Click IP Configuration.
  • Select Static.
  • Configure Engineering-PC2 with these values:
  • Close the Engineering-PC2 window.
  • Return to Engineering-PC1.
  • Click the Desktop tab.
  • Click Command Prompt.
  • Test the Engineering LAN by running this command:
ping 172.16.20.139

What does this command test?

This command sends requests from Engineering-PC1 to Engineering-PC2. Replies prove that Engineering-SW can forward local traffic between its PC ports.

You should see replies from 172.16.20.139. Both department LANs now work independently.

No replies from Engineering-PC2?

Check that both Engineering PCs use 255.255.255.128. Confirm that their addresses end in .138 and .139.

Verify that the PC cables reach FastEthernet0/6 and FastEthernet0/18 on Engineering-SW. Help me troubleshoot the failed local ping between my Engineering PCs.

  • Switch back to Admin-PC1's Command Prompt.

Before you run the next test, do you think local switching is enough to reach Engineering-PC1?

ping 172.16.20.138

This failure is the point

No replies return from Engineering-PC1. The cross-department test ends with packet loss.

Admin-SW can forward frames inside the Administration LAN. R1 has no configured Layer 3 interfaces to carry this traffic into the Engineering LAN.

Did the cross-department ping succeed?

Confirm that you started from the blank Logical workspace provided in the previous step. A reused router may already contain interface configuration.

Check that you have not assigned IPv4 addresses to R1. Help me determine why my cross-department ping succeeds before R1 is configured.

You now have two working switched LANs with a visible routing barrier. Next, you will map the two /25 ranges that create this boundary.

Map the CIDR Ranges

Your switched LANs already carry same-department traffic. The failed cross-department ping exposed the Layer 2 boundary between them.

That failure becomes useful once the CIDR ranges are visible. In this step, you will map both ranges beside the topology in Cisco Packet Tracer.

In this step, get ready to:
  • Convert /25 into the subnet mask used by both departments.
  • Add visible labels for the Administration and Engineering ranges.
  • Match each PC configuration to its labeled range.
Convert the /25 prefix

How Does /25 Define the Range?

An IPv4 address contains 32 bits. A /25 prefix uses 25 bits to identify the network.

That leaves seven bits for addresses inside each block. Seven bits produce 128 total addresses.

Normal LAN use reserves one address for the network. It reserves another address for broadcasts.

Subtracting those two reserved addresses leaves 126 usable host addresses in each block. The dotted mask for this boundary is 255.255.255.128.

  • Check the usable-host calculation as 128 - 2 = 126.
Label both department ranges

Visible notes connect the address calculations to the devices on screen. Each department gets its own note beside its switch.

  • Select the note tool from the right side of the Logical workspace.
  • Click an empty area beside Admin-SW.
  • Create the Administration label by typing this text:
Administration network 172.16.20.0/25
Network address: 172.16.20.0
Subnet mask: 255.255.255.128
Usable hosts: 172.16.20.1 through 172.16.20.126
Usable host count: 126
Broadcast address: 172.16.20.127
Gateway: 172.16.20.1

What Does the Administration Label Show?

The network address identifies the entire Administration range. Hosts can use addresses from 172.16.20.1 through 172.16.20.126.

The broadcast address reaches every host in this range. The default gateway uses the first usable address.

  • Finish the note by selecting an empty area of the workspace.
  • Confirm the Administration label appears beside Admin-SW with all seven lines visible.

Is the Administration Note Hard to Read?

  • Move the note into a larger empty area beside Admin-SW.
  • Check that the final host is 172.16.20.126.
  • Check that the broadcast address is 172.16.20.127.

Help me verify my Administration CIDR label.

  • Select the note tool from the right side of the Logical workspace.
  • Click an empty area beside Engineering-SW.
  • Create the Engineering label by typing this text:
Engineering network 172.16.20.128/25
Network address: 172.16.20.128
Subnet mask: 255.255.255.128
Usable hosts: 172.16.20.129 through 172.16.20.254
Usable host count: 126
Broadcast address: 172.16.20.255
Gateway: 172.16.20.129

Where Does the Second Range Begin?

The Engineering block begins at 172.16.20.128. Its first usable host address is 172.16.20.129.

The final usable host is 172.16.20.254. The address 172.16.20.255 is reserved for broadcasts in this range.

  • Finish the note by selecting an empty area of the workspace.
  • Confirm the Engineering label appears beside Engineering-SW with all seven lines visible.

Does the Engineering Range Look Wrong?

  • Check that the network begins at 172.16.20.128.
  • Check that the usable range begins at 172.16.20.129.
  • Check that the usable range ends at 172.16.20.254.

Help me verify my Engineering CIDR label.

Your topology now shows two equal address blocks. The boundary at 128 separates the departments.

Match each PC to its range

The labels describe the plan. The current PC settings provide evidence that each device follows it.

  • Select Admin-PC1 in the Logical workspace.
  • Select the Desktop tab.
  • Select Command Prompt.
  • Display the full Administration configuration by running:
ipconfig /all

What Does This Command Show?

The command reads the PC's current addressing information. It does not change the configuration.

The displayed address tells you which usable range contains the PC. The mask identifies where that range ends.

  • Match 172.16.20.10 to the Administration usable host range.
  • Confirm the displayed mask is 255.255.255.128.
  • Confirm the displayed gateway is 172.16.20.1.

Admin-PC1 fits inside the Administration range. Its gateway also belongs to that range.

  • Return to the Logical workspace.
  • Select Engineering-PC1.
  • Select the Desktop tab.
  • Select Command Prompt.
  • Display the full Engineering configuration by running:
ipconfig /all

Why Check the Second PC?

Engineering-PC1 uses the same mask as Admin-PC1. Its higher address places it inside the second block.

This comparison proves that matching first three octets do not guarantee that two addresses share a network. The prefix defines the boundary.

  • Match 172.16.20.138 to the Engineering usable host range.
  • Confirm the displayed mask is 255.255.255.128.
  • Confirm the displayed gateway is 172.16.20.129.

Before you test again, do you expect the cross-department ping to succeed while R1 still has no configured IPv4 addresses?

  • Switch back to the Command Prompt on Admin-PC1.
  • Test the path to Engineering-PC1 by running:
ping 172.16.20.138

What Does the Failed Ping Prove?

You should see the ping attempts fail. This is the intended result at this stage.

Admin-PC1 recognizes 172.16.20.138 as a remote address. It sends remote traffic toward 172.16.20.1.

R1 has no active Layer 3 address in either range. The two labels now show exactly why a router is required between the departments.

Did the Cross-Department Ping Reply?

  • Confirm that Admin-PC1 still uses the mask 255.255.255.128.
  • Confirm that Engineering-PC1 still uses the address 172.16.20.138.
  • Confirm that neither R1 interface has an IPv4 address configured.

Help me find why my cross-department ping succeeds before R1 is configured.

You have turned a failed ping into a readable map of the network boundary. Next, you will configure R1 to connect the two labeled ranges.

Configure the Router

The two LANs in Cisco Packet Tracer are fully cabled. Their PC addresses match the labels from the previous step.

The failed ping shows that your switches have reached their Layer 2 boundary. R1 now needs an active Layer 3 interface inside each IPv4 network.

In this step, get ready to:
  • Configure both R1 interfaces with their gateway addresses.
  • Verify that both interfaces are active.
  • Test cross-department communication in both directions.
Give R1 a path into each LAN

Each router interface belongs to one of your labeled networks. Its address also matches the default gateway already configured on that department's PCs.

  • In the Logical workspace from earlier, click R1.
  • Select the tab for the command-line interface.
  • Wait until you see the Router> prompt.
  • Apply the interface addresses and display their status by entering each line below:

Before you enter these commands, predict whether both interfaces will report active status afterward.

enable
configure terminal
interface GigabitEthernet0/0/0
ip address 172.16.20.1 255.255.255.128
no shutdown
exit
interface GigabitEthernet0/0/1
ip address 172.16.20.129 255.255.255.128
no shutdown
end
show ip interface brief

What does this configuration do?

  • The enable command enters privileged EXEC mode.
  • The configure terminal command enters global configuration mode.
  • The first interface command selects the connection to Admin-SW.
  • The first ip address command assigns the Administration gateway address.
  • The second interface command selects the connection to Engineering-SW.
  • The second ip address command assigns the Engineering gateway address.
  • Each no shutdown command enables its selected interface.
  • The show ip interface brief command summarizes the interface addresses and status.

The row for GigabitEthernet0/0/0 should list 172.16.20.1 with an up status. The row for GigabitEthernet0/0/1 should list 172.16.20.129 with an up status.

That is the routing bridge in place. R1 now has an active connection inside each department's network.

Interfaces not showing the intended status?

  • Compare each interface name with GigabitEthernet0/0/0 or GigabitEthernet0/0/1.
  • Confirm that each interface received its own no shutdown command.
  • Re-enter any address that differs from the matching CIDR label.

Help me diagnose why an R1 interface is not showing the intended address or active status.

✔️ Awesome, I've got everything!

Your R1 configuration matches both CIDR labels.

ⓧ I'd like to double check the full code

enable
configure terminal
interface GigabitEthernet0/0/0
ip address 172.16.20.1 255.255.255.128
no shutdown
exit
interface GigabitEthernet0/0/1
ip address 172.16.20.129 255.255.255.128
no shutdown
end
show ip interface brief

What should match?

This is the complete R1 command sequence for this step. It assigns both gateway addresses.

It also activates both interfaces before displaying their status.

Test communication in both directions

A default gateway gives each PC a route toward remote networks. Your cross-department ping now tests whether both gateway interfaces can forward that traffic.

  • Return to the Logical workspace.
  • Click Admin-PC1.
  • Select Desktop.
  • Select Command Prompt.

Before you test, predict whether Admin-PC1 can now reach Engineering-PC1.

  • Test the path from Admin-PC1 to Engineering-PC1 by running:
ping 172.16.20.138

What does this test prove?

Admin-PC1 treats 172.16.20.138 as a remote address. It sends the traffic to its configured gateway at 172.16.20.1.

R1 forwards the traffic through its Engineering interface. A reply proves that the route works from Administration to Engineering.

You should see replies from 172.16.20.138. A first timeout can occur while the devices resolve local addresses.

  • Repeat the same ping from Admin-PC1 if the first attempt includes a timeout.
  • Return to the Logical workspace.
  • Click Engineering-PC1.
  • Select Desktop.
  • Select Command Prompt.
  • Test the reverse path from Engineering-PC1 to Admin-PC1 by running:
ping 172.16.20.10

Why test the reverse path?

The reverse ping checks the Engineering gateway at 172.16.20.129. It also confirms that R1 can forward traffic toward the Administration network.

You should see replies from 172.16.20.10. You have now proved that both departments can communicate through R1.

Cross-department ping still failing?

  • Confirm that GigabitEthernet0/0/0 uses 172.16.20.1 with mask 255.255.255.128.
  • Confirm that GigabitEthernet0/0/1 uses 172.16.20.129 with mask 255.255.255.128.
  • Check that Admin-PC1 still uses 172.16.20.1 as its default gateway.
  • Check that Engineering-PC1 still uses 172.16.20.129 as its default gateway.

Help me troubleshoot a failed cross-department ping after configuring R1.

Your router now connects both departments across their separate CIDR ranges. Next, you will inspect the forwarding information that the switches and R1 learned from this traffic.

Inspect Forwarding State

Your routed network in Cisco Packet Tracer now carries traffic between Administration and Engineering. The next goal is to reveal the forwarding state behind those successful replies.

A successful ping hides the decisions inside each device. You will inspect each switch's MAC address table. Then you will connect R1's connected routes to the traced path.

In this step, get ready to:
  • Generate recent traffic across both LANs.
  • Match dynamic MAC entries to each switch port.
  • Connect R1's routes to the traced packet path.
Generate recent traffic

Ethernet switches learn from the source MAC address in each frame. Fresh traffic repopulates their tables with entries that match your current topology.

  • Return to Admin-PC1's Command Prompt from the earlier connectivity test.
  • Generate recent Administration traffic by running these commands:
ping 172.16.20.11
ping 172.16.20.138

What does this traffic create?

  • The first ping sends local frames between Admin-PC1 and Admin-PC2.
  • The local exchange gives Admin-SW traffic on FastEthernet0/6 plus FastEthernet0/18.
  • The second ping sends routed traffic through the router-facing FastEthernet0/1 port.

You should see successful replies during both tests. These replies confirm that Admin-SW has recently handled local traffic plus routed traffic.

Missing replies from Administration?

Confirm that Admin-PC1 still uses 172.16.20.10 with gateway 172.16.20.1. Repeat the affected command if the first request was delayed by address resolution.

Check that Admin-PC1 remains connected to Admin-SW on FastEthernet0/6.

Ask for help with the traffic test.

  • Return to Engineering-PC2's Command Prompt from the earlier connectivity test.
  • Generate recent Engineering traffic by running this command:
ping 172.16.20.138

Why ping from Engineering-PC2?

  • Engineering-PC2 sends frames into Engineering-SW through FastEthernet0/18.
  • Engineering-PC1 returns frames through FastEthernet0/6.
  • The earlier cross-department traffic gives the switch recent frames on router-facing FastEthernet0/1.

You should see replies from Engineering-PC1. Engineering-SW now has fresh local traffic to learn from.

Missing the Engineering replies?

Confirm that Engineering-PC2 still uses 172.16.20.139 with subnet mask 255.255.255.128.

Check that Engineering-PC2 remains connected to Engineering-SW on FastEthernet0/18.

Ask for help with the local Engineering test.

Inspect each switch's MAC table

Each learned row pairs a source MAC address with the port where its frame arrived. The switch uses that mapping to send later frames toward the correct device.

  • Select Admin-SW in the Logical workspace.
  • Open its command-line interface.
  • Display Admin-SW's learned entries by running these commands:
enable
show mac address-table

How do I read the table?

  • The Vlan column groups the learned entries.
  • The Mac Address column identifies each frame source.
  • The Type column shows how each entry was learned.
  • The Ports column maps each source to its switch interface.

You should find dynamic entries associated with FastEthernet0/6, FastEthernet0/18, and FastEthernet0/1. This is visible proof that Admin-SW learned from both PCs plus R1.

  • Select Engineering-SW in the Logical workspace.
  • Open its command-line interface.
  • Repeat the two commands above to display Engineering-SW's learned entries.

You should again find dynamic entries associated with FastEthernet0/6, FastEthernet0/18, and router-facing FastEthernet0/1. Both switches now show how recent frames entered their LANs.

Missing a learned switch port?

Repeat the relevant ping from the previous substep. MAC entries can disappear after a period without traffic.

Confirm that you are inspecting the intended switch. Match its device name to the visible department label.

Ask for help matching the table to the topology.

Confirm routes, trace the path, and save

R1 adds a connected route for each active interface network. Those routes explain why the router can move packets across the /25 boundary.

  • Select R1 in the Logical workspace.
  • Return to its command-line interface from the previous step.

Before you run this check, which two labeled networks do you expect R1 to list as directly connected?

  • Display only R1's connected networks by running this command:
show ip route connected

What do the connected routes show?

  • The route for 172.16.20.0/25 uses GigabitEthernet0/0/0.
  • The route for 172.16.20.128/25 uses GigabitEthernet0/0/1.
  • Each route exists because its R1 interface has an address inside that network.

Missing a connected route?

Return to the interface summary from the previous step. Confirm that both intended interfaces remain up.

Check that each interface still has its intended /25 address. A connected route depends on an active addressed interface.

Ask for help restoring the route.

A route table describes the networks R1 can reach directly. A path trace shows that forwarding decision from the PC's point of view.

  • Return to Admin-PC1's Command Prompt from earlier.

Before you trace the path, which device do you expect to appear between Admin-PC1 and Engineering-PC1?

  • Trace the cross-department path by running this command:
tracert 172.16.20.138

What does the trace prove?

  • The first routed hop is R1 at 172.16.20.1.
  • The destination is Engineering-PC1 at 172.16.20.138.
  • The trace connects Admin-PC1's default gateway to R1's two connected routes.

You should see R1 on the path before Engineering-PC1. That result ties the PC's packet path to the router state you just inspected.

Trace missing the destination?

Repeat the successful cross-department ping before running the trace again. This confirms that connectivity still works.

Check that Admin-PC1 still uses 172.16.20.1 as its default gateway.

Ask for help reading the traced path.

A saved PKT file preserves the topology plus every configuration you inspected. Saving now gives you a working lab that you can reopen or share.

  • Return to the Logical workspace.
  • Select File from the top menu.
  • Select Save As.
  • Choose a Windows folder that you can find again.
  • Record the selected location here: your chosen Windows folder.
  • Enter two-department-office.pkt as the project filename.
  • Select Save.

Packet Tracer saves the working two-department topology in your chosen Windows folder.

  • Select File from the top menu.
  • Select Save As.
  • Confirm that two-department-office.pkt appears in your chosen Windows folder.
  • Close the Save As window after confirming the file.

You now have device-level proof of how the office network forwards traffic. Your saved lab captures the learned switch ports, R1's routed path, and a working two-department topology.

Secret mission

Break and Repair a Subnet Mask

One PC can make the wrong forwarding choice while every cable remains correct. You will change Engineering-PC2's mask to reproduce the fault. You will diagnose the decision before restoring the working /25.

Clean Up Your Resources

Clean Up Your Resources

Your Cisco Packet Tracer network lab uses only local disk space on your Windows PC. There are no paid cloud resources or ongoing costs.

Resources you used:

  • Cisco Packet Tracer installed on your Windows PC.
  • The repaired two-department-office.pkt project saved in your chosen Windows folder.

Keep everything running

Keeping the lab preserves your simulator plus the working topology for future networking practice.

  • Keep Cisco Packet Tracer installed on this Windows PC.
  • Retain two-department-office.pkt in your chosen Windows folder.
  • Keep your NetAcad account active for future Packet Tracer sign-ins.

Pause - I'll come back to this later

Closing Packet Tracer frees the memory it is using. Your saved project stays ready for another session.

  • Close the Cisco Packet Tracer window.
  • Leave two-department-office.pkt in your chosen Windows folder.
  • Double-click two-department-office.pkt in that folder when you are ready to continue.

Delete - I don't want to use this again

Deleting your finished lab feels drastic. This option removes the local simulator plus the saved project so you can start fresh.

  • Search Windows for Installed apps.
  • Open the matching settings page.
  • Find Cisco Packet Tracer in the apps list.
  • Select Cisco Packet Tracer.
  • Use the uninstall option for Cisco Packet Tracer.
  • Follow the Windows prompts to complete the removal.
  • Return to Installed apps after the uninstall finishes.
  • Confirm that Cisco Packet Tracer no longer appears in the apps list.

The simulator is now removed from Windows. The saved Packet Tracer project remains in your chosen folder until you delete it.

  • Use Windows file browsing to open the chosen folder where your project is saved.
  • Select two-department-office.pkt.
  • Delete two-department-office.pkt.
  • Confirm that two-department-office.pkt is no longer listed in the chosen Windows folder.

The local lab is gone. Your NetAcad account remains active for future Cisco training.

Nice Work!

Nice Work!

You completed your two-department office network in Cisco Packet Tracer! Traffic now crosses both /25 department networks through R1.

What you learned:

  • Built two Ethernet LANs with four PCs across two Cisco 2960 switches. Proved that local traffic succeeds through a switch before routing exists.
  • Calculated both department /25 ranges using CIDR. Your topology labels now make each network boundary visible.
  • Configured R1 to route traffic between both departments. Proved MAC address learning by matching dynamic entries to switch ports. Confirmed the router's connected routes. Traced a packet from Administration to Engineering.
  • Secret Mission: Broke Engineering-PC2 with an incorrect /24 subnet mask. Used the working local ping to rule out its cable path. Used the failed remote ping to expose the addressing fault. Restored /25 to recover end-to-end communication.

Ready to quiz yourself?