Build and Troubleshoot a Network

Build a two-PC LAN, fix IP faults, and map your Windows network.

Introduction

30 Second Summary

A green connection light can look reassuring while one computer still cannot reach another. Every failed check leaves evidence about where communication stopped.

In this project, you will build a two-PC LAN in Cisco Packet Tracer that returns successful ping replies. You will practice a repeatable troubleshooting process in the simulator before applying it to your real Windows connection.

What You'll Build

Watch a network you built recover from a deliberate addressing fault through your own troubleshooting.

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

  • A working two-PC LAN that sends successful ping replies through a switch.
  • A break-and-repair workflow that uses failed tests to isolate an addressing fault.
  • A map of your real Windows connection that follows traffic from its IPv4 address through its default gateway to internet routing hops. The adapter record also includes its subnet mask. A DNS lookup confirms how names become addresses.
  • Secret Mission: Diagnose a subtler subnet-mask mismatch to restore connectivity without replacing the topology.

Are there any prerequisites?

A Windows computer with internet access plus administrator permission to install software is required. Step 1 covers the Cisco Networking Academy account setup plus Cisco Packet Tracer installation for complete beginners.

Before We Start

Before the hands-on work begins, lock in what you are building and how you will approach each result. You will treat every failed ping as evidence that narrows down why your two-PC LAN cannot communicate.

Set Up Cisco Packet Tracer

Changing settings on your real home network can cut off the connection you rely on. Cisco Packet Tracer gives you a safe simulator where every mistake stays inside the lab.

Access to the simulator comes through Cisco Networking Academy. This step takes you from account enrollment to an empty Logical workspace.

In this step, get ready to:
  • Access the free current Windows download with a signed-in Cisco Networking Academy account.
  • Install Cisco Packet Tracer at the default destination.
  • Keep multi-user mode off during login to reach the empty Logical workspace.

Why Packet Tracer for this lab?

Windows diagnostics show your live connection. They do not let you control its topology or create a repeatable fault safely.

Packet Tracer gives you a controlled network you can build, break, and repair without touching your home connection.

Access the Windows download

Cisco updates its enrollment page labels over time. The live flow keeps your account connected to the current Windows download.

Account creation can feel like a hurdle before the real lab. Cisco provides this learning access for free.

  • Open the official Cisco Packet Tracer page.
  • Follow the page's current enrollment flow.
  • Create your Cisco Networking Academy account with the details requested by the enrollment flow.
  • Complete the sign-in flow.
  • Open the Cisco Resource Hub.
  • Select the download appropriate for Windows.
  • Check your browser's download list for the Packet Tracer installer.

Good start. Your signed-in account now gives you access to the installer for the lab.

Can't access the Windows download?

  • Confirm your browser is signed in to the Cisco Networking Academy account used for enrollment.
  • Return to the Packet Tracer page if the Windows download is missing.
  • Finish the current enrollment flow before checking the Resource Hub again.

If the download remains unavailable, help me troubleshoot my Cisco Networking Academy access.

Install Cisco Packet Tracer

The Windows installer adds Packet Tracer to your computer. Keeping the default destination makes the application easier to locate later.

Windows may ask for administrator approval before the installer continues. This is the permission you confirmed before starting the project.

  • Open your browser's download list.
  • Double-click the downloaded Cisco Packet Tracer Windows installer.
  • Approve the administrator request if Windows shows one.
  • Accept the License Agreement.
  • Keep the default destination unless you prefer another location.
  • Review the installer settings.
  • Click Install.

You'll see the installation progress move toward completion. That progress confirms Windows is copying the application files.

  • Keep Launch Cisco Packet Tracer checked on the completion page.
  • Click Finish.

You'll see Packet Tracer open to its first-launch multi-user prompt. This prompt confirms the installation completed successfully.

Installer not opening?

  • Wait for the browser download to finish before opening the installer again.
  • Retry the installer from a Windows account with administrator permission.
  • Use Windows search to find Cisco Packet Tracer if the application does not launch after installation.

If installation still fails, help me troubleshoot my Packet Tracer installation.

Complete the first-launch login

The first launch asks whether Packet Tracer should start in multi-user mode. This lab uses one local workspace, so multi-user mode stays off.

  • Click No when Would you like to run multi-user when the application starts? appears.
  • Click LOGIN in the Cisco Packet Tracer Login window.
  • Complete your Cisco account sign-in in the browser.
  • Confirm the browser shows You have successfully logged in to Cisco Packet Tracer. You may close this tab..
  • Close the browser tab.
  • Return to Cisco Packet Tracer.

Before you check the workspace, what do you expect Packet Tracer to show after a successful login?

  • Check that Logical is selected in the workspace.

You'll see an empty Logical topology workspace ready for devices. This confirms Packet Tracer is installed and signed in without multi-user mode running.

Login flow not completing?

  • Select LOGIN again if the browser did not open.
  • Complete the browser sign-in before returning to Packet Tracer.
  • Close the browser tab only after the successful login confirmation appears.

If Packet Tracer continues waiting after the browser confirms success, help me troubleshoot the Packet Tracer login flow.

Setup is complete. Next, you'll turn that empty workspace into a two-PC network that can exchange successful ping replies.

Build a Working LAN

You completed the Cisco Packet Tracer login flow. The empty Logical workspace is ready for your first LAN.

A successful two-host connection gives you a visible baseline before you create a fault. Every later ping result has something trustworthy to compare against.

In this step, you will connect two PCs through a switch. You will use ping to prove that traffic reaches PC-B.

In this step, get ready to:
  • Build the three-device topology.
  • Configure both PCs on one IPv4 subnet.
  • Save a topology that returns successful ping replies.
Build the switched topology

The switch gives both PCs a shared connection point. Each PC uses its FastEthernet0 interface to reach a separate switch port.

  • Select End Devices from the device categories in the bottom-left corner.
  • Drag one generic PC into the Logical workspace.
  • Drag a second generic PC into the workspace.
  • Select Switches from the device categories.
  • Drag one 2960 switch between the two PCs.
  • Click the first PC in the workspace.
  • Select the Config tab.
  • Replace the Display Name with PC-A.

You should now see PC-A beneath the first PC in the workspace.

  • Close the PC-A configuration window.
  • Click the second PC in the workspace.
  • Select the Config tab.
  • Replace the Display Name with PC-B.
  • Close the PC-B configuration window.

Your workspace should now contain PC-A. It should also contain PC-B beside one 2960 switch.

  • Select Connections from the device categories in the bottom-left corner.
  • Select Copper Straight-Through from the available cable types.
  • Click PC-A in the workspace.
  • Select FastEthernet0 from the interface list.
  • Click the 2960 switch.
  • Select FastEthernet0/1 from the switch port list.

A cable now runs from PC-A to the switch. Its indicators may begin in different colours while the link starts.

  • Select Copper Straight-Through again.
  • Click PC-B in the workspace.
  • Select FastEthernet0 from the interface list.
  • Click the 2960 switch.
  • Select FastEthernet0/2 from the switch port list.

Link indicators can stay amber for up to about a minute while the switch converges. That brief pause is expected.

  • Wait until both ends of each cable show green indicators.

You have the cabling layer working now. Both PCs have live paths to separate switch ports.

Links staying amber or red?

Check that both links use Copper Straight-Through cables.

Confirm each PC uses FastEthernet0. Confirm the switch connections use separate FastEthernet ports.

If the indicators still do not turn green, help me check my Packet Tracer links.

Configure both PC addresses

Each PC needs a static IPv4 address before it can exchange traffic. A subnet mask tells each host which addresses belong to its local network.

A default gateway carries traffic beyond the local network. This LAN has no router, so the gateway field stays blank.

  • Click PC-A in the Logical workspace.
  • Select the Desktop tab.
  • Select IP Configuration.
  • Enter 192.168.1.10 in the IP address field.
  • Enter 255.255.255.0 in the subnet mask field.
  • Leave the default gateway field blank.
  • Close the PC-A window.

PC-A now has the first host address in your lab. Its configuration panel should show 192.168.1.10 with the mask 255.255.255.0.

  • Click PC-B in the workspace.
  • Select the Desktop tab.
  • Select IP Configuration.
  • Enter 192.168.1.20 in the IP address field.
  • Enter 255.255.255.0 in the subnet mask field.
  • Leave the default gateway field blank.
  • Close the PC-B window.

Both PCs now see the same local network through the same mask. Their different host addresses let Packet Tracer deliver traffic to the correct PC.

Test and save the working LAN

The green links confirm that the cable path is active. A successful ping confirms that the addressing also works.

  • Click PC-A in the workspace.
  • Select the Desktop tab.
  • Select Command Prompt.

Before you run the test, do you expect PC-A to receive replies from PC-B?

  • Test the path to PC-B twice by entering this command two times:
ping 192.168.1.20

What does this command prove?

  • The ping command sends ICMP echo requests to PC-B.
  • Echo replies prove that PC-A can reach the configured address through the switch.
  • The first run may be affected while Packet Tracer resolves the destination address. The second run gives you the reliable baseline.

On the second run, you should see replies from 192.168.1.20. That result proves the complete two-PC path works.

Ping still failing?

Confirm PC-A uses 192.168.1.10 with the mask 255.255.255.0.

Confirm PC-B uses 192.168.1.20 with the same mask. Check that both links remain green.

If the second test still fails, help me diagnose my two-PC ping.

  • Close the PC-A window.
  • Select File from the Packet Tracer menu bar.
  • Select Save As.
  • Choose a folder you can return to during the next steps.
  • Enter working-lan.pkt as the file name.
  • Confirm the save in the Windows file dialog.

You should now see working-lan.pkt as the open file name in Packet Tracer. Your known-good baseline is saved.

Your working LAN is ready for controlled troubleshooting. Next, you will change one address to see how a logical fault behaves.

Break the Network on Purpose

Your working LAN now gives you a trustworthy baseline. PC-A can reach PC-B through the switch.

Green links in Cisco Packet Tracer prove physical connectivity. A controlled address change lets you test whether the IPv4 configuration can still carry traffic.

In this step, get ready to:
  • Preserve the successful baseline as a separate file.
  • Place PC-B on a different IPv4 subnet.
  • Test the changed network from PC-A.
Preserve the working baseline

A saved baseline gives you a known-good network for comparison. Creating a separate copy protects that evidence while you introduce the fault.

  • Click File in the top menu.
  • Select Save As.
  • Confirm working-lan.pkt is listed in the current folder.
  • Save the copy as broken-lan.pkt in the same folder.

You now have a separate copy for the controlled fault. The successful configuration remains protected in working-lan.pkt.

Change PC-B's IPv4 address

Changing one address keeps every physical detail constant. This isolates the IP configuration as the only variable in your test.

  • Select PC-B in the logical workspace.
  • Click the Desktop tab.
  • Click IP Configuration.
  • Replace PC-B's IPv4 address with 192.168.2.20.
  • Leave the subnet mask set to 255.255.255.0.
  • Keep the default gateway blank.

You should still see both links in green. That confirms the physical topology did not change.

Test the changed network

The ping command uses ICMP echo messages to test IP-level reachability. The result shows whether PC-A can communicate with PC-B at its new address.

  • Select PC-A in the logical workspace.
  • Click the Desktop tab.
  • Click Command Prompt.

Before you run the test, do you think the green links are enough for PC-A to reach PC-B's new address?

  • Test PC-A's reachability to PC-B by running this command:
ping 192.168.2.20

What does this test check?

The command asks PC-B at 192.168.2.20 to return echo replies. Those replies would prove that traffic can travel between the two IPv4 configurations.

You should see the test fail without successful replies from 192.168.2.20. This is the intended evidence that green links do not prove a working IP configuration.

Ping succeeds unexpectedly?

  • Return to PC-B's Desktop tab.
  • Confirm IP Configuration shows 192.168.2.20.
  • Confirm PC-A tested 192.168.2.20.

If replies continue, help me compare the two Packet Tracer PC configurations.

  • Return to the logical workspace.
  • Click File in the top menu.
  • Select Save As.
  • Save the changed topology as broken-lan.pkt in the same folder as working-lan.pkt.
  • Confirm replacement if Windows asks.

You have created a controlled failure while preserving the working baseline. The failed ping is now repeatable evidence stored in broken-lan.pkt.

Your broken network now contains one deliberate fault with every cable left untouched. Next, you will compare the PC configurations to isolate the mismatch before repairing it.

Diagnose and Repair the Fault

The green links in your Cisco Packet Tracer lab prove the physical path still exists. The failed ping points toward the logical configuration.

A configuration-first check protects the evidence before you change anything. Comparing both PCs turns the failure into a specific diagnosis.

In this step, get ready to:
  • Inspect the full configuration of both simulated PCs.
  • Identify the IPv4 subnet mismatch.
  • Restore PC-B to the original subnet.
Inspect both PC configurations

The full configuration view gives you a consistent snapshot of each host. That snapshot lets you compare evidence without changing the topology.

  • Click PC-A in the logical workspace.
  • Select the Desktop tab.
  • Select Command Prompt.
  • Show PC-A's full TCP/IP configuration by running this command:
ipconfig /all

What does this command reveal?

  • The IPv4 address identifies PC-A on the LAN.
  • The subnet mask defines which addresses PC-A treats as local.
  • The blank default gateway matches this isolated LAN.

PC-A should show IPv4 address 192.168.1.10. Its subnet mask should be 255.255.255.0.

  • Move PC-A's device window aside so its output remains visible.
  • Click PC-B in the logical workspace.
  • Select the Desktop tab.
  • Select Command Prompt.
  • Show PC-B's full configuration by running the same command:
ipconfig /all

Why run the same check?

  • This snapshot gives you the same configuration fields for PC-B.
  • The unchanged green links keep the physical layer constant.
  • The matching output format makes the addressing difference easier to isolate.

PC-B should show IPv4 address 192.168.2.20. Its subnet mask should be 255.255.255.0.

Can't compare the configurations?

  • Check that you selected Command Prompt from each PC's Desktop tab.
  • Run the command again if one configuration has scrolled out of view.

If the values still look unclear, help me compare the two simulated PC configurations.

Compare the subnet evidence

For this lab, 255.255.255.0 is a /24 mask. The first three address numbers identify the local network.

  • Place the two simulated command windows side by side.
  • Compare the IPv4 address entries.
  • Compare the subnet mask entries.

PC-A belongs to 192.168.1.0/24. Broken PC-B belongs to 192.168.2.0/24.

What does the comparison prove?

The shared /24 mask places the two addresses on different local networks. PC-A treats 192.168.2.20 as a remote address.

The switch forwards local Ethernet traffic. The blank gateway leaves no device to route traffic between these two networks.

Restore PC-B and verify the repair

The evidence isolates one incorrect value on PC-B. A narrow repair preserves every part of the topology that already works.

  • Return to PC-B's Desktop tab from earlier.
  • Select IP Configuration.
  • Replace PC-B's IPv4 address with 192.168.1.20.
  • Confirm PC-B's subnet mask remains 255.255.255.0.
  • Leave the default gateway blank.

The physical links remain green because this repair changes only the logical address.

  • Return to PC-A's Command Prompt from earlier.

Before you rerun the test, what should PC-A receive now that both hosts share one subnet?

  • Test the repaired connection twice by running these commands:
ping 192.168.1.20
ping 192.168.1.20

What does this test prove?

  • The ping command sends ICMP echo requests from PC-A to PC-B.
  • Successful replies prove that the corrected address restores communication.
  • The second run is the final checkpoint for this repaired LAN.

On the second run, you should see replies from 192.168.1.20. That is the repair confirmed: PC-A can reach PC-B again.

Still seeing a failed ping?

  • Confirm PC-B's IPv4 address is 192.168.1.20.
  • Confirm both PCs use subnet mask 255.255.255.0.
  • Keep both default gateways blank.

If PC-A still cannot reach PC-B, help me debug the repaired Packet Tracer LAN.

  • Select File from the Packet Tracer top menu.
  • Select Save As.
  • Save the repaired copy as repaired-lan.pkt in the folder containing your other Packet Tracer files.
  • Confirm the open file name shows repaired-lan.pkt.

You turned a failed ping into a precise diagnosis and a verified repair. Next, you'll map the same network clues on your real Windows connection.

Map Your Real Windows Network

Your repaired Cisco Packet Tracer LAN proved that matching IPv4 settings restore communication. The same evidence-first habit applies to the network your Windows computer uses every day.

Windows Command Prompt reveals the settings behind your active connection. You will map its IPv4 address and subnet mask.

Next, you will test the default gateway. Separate checks reveal how DNS responds before tracing an internet route.

In this step, get ready to:
  • Record the active Windows adapter's IPv4 configuration.
  • Test the default gateway's response.
  • Map the path from DNS resolution to the first routing hop.
Map your active adapter

A Windows computer can list virtual adapters beside the connection carrying your traffic. The active adapter gives you the local values that matter for this map.

  • Press the Windows key to open the search bar.
  • Type Command Prompt into the search field.
  • Press Enter to open Windows Command Prompt.
  • Inspect every adapter's full TCP/IP configuration by running this command:
ipconfig /all

What does ipconfig /all reveal?

  • The ipconfig /all command lists the full TCP/IP configuration for every adapter.
  • The active adapter supplies the observed address information for your Windows network map.

This output can feel crowded because Windows lists disconnected adapters and virtual adapters too.

  • Locate the adapter entry that contains the default gateway used by your current internet connection.
  • Record the adapter's IPv4 address here: your Windows IPv4 address.
  • Record the adapter's subnet mask here: your Windows subnet mask.
  • Record the adapter's default gateway here: your default gateway address.
  • Record the adapter's DNS server entries here: your DNS server entries.

That busy list is now useful: your active adapter has a four-part map you can test.

Can't identify the active adapter?

  • Ignore adapters described as disconnected.
  • Focus on the adapter that includes the default gateway for your current connection.

If several adapters still look active, help me identify the correct Windows network adapter.

Test your gateway and DNS

The default gateway is the next device your computer uses to leave its local network. A ping test asks whether it answers ICMP echo traffic.

Before you test the gateway, make a quick prediction about whether it will answer an ICMP echo request.

  • Test the recorded gateway by running this command:
ping [[DEFAULT_GATEWAY="your default gateway address"]]

What does this gateway test prove?

The ping command sends ICMP echo requests to the gateway you recorded. Replies prove that the gateway answers this type of local traffic.

Your result is useful either way. A missing reply only shows that the gateway did not answer the echo request.

  • Record the gateway test result here: your gateway ping result.

No reply from the gateway?

  • Continue with the DNS test because some gateways ignore ICMP echo requests.
  • Confirm Windows still shows an active internet connection if the later tests also fail.

If you need another pair of eyes, help me interpret my default gateway ping result.

DNS tests whether your configured name service can translate a domain into an address. This check can succeed even when the gateway chooses not to answer a ping.

  • Test the configured DNS service by running this command:
nslookup bing.com

What does this DNS test show?

The nslookup command asks the configured DNS service about bing.com. Its output identifies the responding DNS server and the returned address information.

You should see a response that identifies a DNS server. You should also see address information for bing.com.

  • Record the DNS server that answered here: the DNS server that answered.

DNS lookup not returning an answer?

  • Confirm the active adapter listed at least one DNS server.
  • Check that your Windows computer can still reach websites.

For help narrowing down the failure, help me troubleshoot my Windows DNS lookup.

You have now separated local gateway behavior from name resolution behavior.

Trace the route beyond your LAN

A route trace reveals the numbered hops between your computer and an internet destination. Each response gives you another piece of evidence about how traffic leaves your local network.

Before you trace the route, predict whether every hop will return an address.

  • Trace the route toward Microsoft's website by running this command:
tracert /d www.microsoft.com

What does this route trace reveal?

  • The tracert command follows the route toward the destination.
  • The /d option keeps intermediate hops as IP addresses.
  • The numbered rows show how far each probe travels before receiving a response.

You should see numbered hops containing IP addresses or * entries. These hops show the route leaving your local network.

Each * represents an individual hop that did not answer. It does not automatically prove that the end-to-end route failed.

Route trace not reaching the destination?

  • Confirm your internet connection still works in a browser.
  • Look for later numbered hops after any * entries before treating the route as failed.

If the output remains unclear, help me interpret my Windows route trace.

  • Record the first numbered hop here: your first route hop.
  • Record the observed route behavior here: your observed route behavior.
  • Compare the first hop's role with the blank gateway in your repaired Packet Tracer LAN.

Why does the first hop matter?

The first responding hop usually represents the first routing device beyond your computer. Your isolated Packet Tracer LAN has no router, so its PCs keep the default gateway blank.

You have closed the loop between the simulator and your real connection: addresses identify hosts, gateways lead beyond the LAN, DNS resolves names, and routing hops reveal the path.

Secret mission

Diagnose a Subnet-Mask Mismatch

Two IPv4 addresses can look close while their subnet masks draw different local boundaries. Diagnose that disagreement without replacing the topology, then restore communication between both PCs.

Clean Up Your Resources

Clean Up Your Resources

This project runs entirely on your Windows computer, so there are no ongoing costs. Your three options are to keep the lab ready, pause it, or remove the local resources.

Resources you used:

  • Cisco Packet Tracer installation on your Windows computer.
  • The original working baseline in working-lan.pkt.
  • The intentional addressing fault in broken-lan.pkt.
  • The repaired baseline in repaired-lan.pkt.
  • The completed subnet-mask challenge in subnet-mission-complete.pkt.

Keep everything running

No action is needed. Choose this option if you want to repeat the faults or extend the network later.

  • Leave Cisco Packet Tracer installed on your Windows computer.
  • Keep your Cisco Networking Academy account available for future networking labs.
  • Retain working-lan.pkt as your successful baseline.
  • Retain broken-lan.pkt as your addressing-fault example.
  • Retain repaired-lan.pkt as your repaired baseline.
  • Retain subnet-mission-complete.pkt as evidence of the completed subnet-mask diagnosis.

Pause - I'll come back to this later

Pausing frees local memory while preserving every lab file for later. Nothing continues running or accumulating cost.

  • Close Cisco Packet Tracer.
  • Close Windows Command Prompt.
  • Keep Cisco Packet Tracer installed.
  • Keep working-lan.pkt, broken-lan.pkt, repaired-lan.pkt, and subnet-mission-complete.pkt in their saved locations.

Delete - I don't want to use this again

Remove the local lab resources if you want to start fresh. Your free Cisco Networking Academy account remains available because this cleanup does not close it.

  • Close Cisco Packet Tracer.
  • Use Windows Settings to uninstall Cisco Packet Tracer.
  • Locate each saved lab file using Windows search.
  • Delete working-lan.pkt from its saved location.
  • Delete broken-lan.pkt from its saved location.
  • Delete repaired-lan.pkt from its saved location.
  • Delete subnet-mission-complete.pkt from its saved location.

After cleanup, searching your computer for each .pkt filename should return no saved project file.

Nice Work!

Nice Work!

Well done! Your Cisco Packet Tracer lab now proves that a two-PC LAN can fail for logical reasons even while every physical link stays green. Your Windows network map carries the same troubleshooting workflow onto the connection you use every day.

You've learned how to:

  • Build a switched two-PC LAN with static IPv4 addresses. Prove connectivity through successful ping replies.
  • Preserve a working baseline before creating an intentional addressing fault. Compare host configurations to isolate the subnet mismatch. Restore successful communication without touching the green links.
  • Map your active Windows adapter's IPv4 settings. Test the default gateway from Windows Command Prompt. Identify the DNS server answering the lookup. Trace the routing hops toward an internet destination.
  • Complete the optional Secret Mission by diagnosing PC-B's smaller subnet mask. Restore successful replies without replacing the topology.

Ready to quiz yourself?