Build a Multi-Subnet Office Network

Plan IPv4 subnets and configure a multi-department network in Packet Tracer.

Introduction

30 Second Summary

In any office, different departments need their own network space so broadcasts from one team don't flood another. The way real networks solve this is by dividing one big IP address range into smaller pieces called subnets.

In this project, you will divide a single /24 network into 3 subnets and build a fully working multi-department office network in Cisco Packet Tracer. You'll configure a router via the command line to connect all departments so they can communicate across subnet boundaries.

What You'll Build

A simulated office network for a company with 3 departments (Sales, Engineering, HR), each on its own subnet carved from 192.168.1.0/24, connected by a central router.

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

  • A complete subnetting plan that divides a /24 network into 3 usable subnets with correct network addresses, host ranges, and broadcast addresses.
  • A working multi-subnet network in Packet Tracer with 1 router, 3 switches, and 6 PCs that can all ping each other across subnets.
  • Hands-on experience configuring Cisco IOS router interfaces via the CLI, directly mapping to CCNA exam objective 1.6 (Configure and verify IPv4 addressing and subnetting).
  • Secret Mission: Add a 4th department using Variable Length Subnet Masking (VLSM) to efficiently allocate addresses based on department size.

Are there any prerequisites?

This project assumes you have a basic understanding of what IP addresses are and familiarity with the OSI model. You'll also need Cisco Packet Tracer installed (free with a Cisco Networking Academy account).

Create Your Subnetting Plan

Before placing a single device in Packet Tracer, you need a plan. Every IP address, every subnet boundary, and every device assignment should be calculated on paper first.

In this step, you'll learn how subnetting divides a single network into smaller pieces. Then you'll calculate the exact addresses for your 3-department office network.

In this step, get ready to:
  • Understand how borrowing host bits creates subnets.
  • Calculate network, host range, and broadcast addresses for 3 subnets.
  • Assign specific IP addresses to the router and all 6 PCs.
Understand how subnetting works

Your office has 3 departments that each need their own isolated network segment. You've been given a single network: 192.168.1.0/24. Your job is to divide it into 3 smaller networks called subnets.

What is subnetting?

Subnetting is the process of splitting one large network into multiple smaller networks. Each smaller network (subnet) gets its own range of IP addresses and operates independently.

This maps directly to CCNA exam objective 1.6: Configure and verify IPv4 addressing and subnetting. It's one of the most tested skills on the exam.

Here's the key math behind subnetting 192.168.1.0/24:

  • The /24 means the first 24 bits are the network portion, leaving 8 bits for hosts. That's 2^8 = 256 total addresses.
  • To create subnets, you "borrow" bits from the host portion. Borrowing 2 bits gives you 2^2 = 4 subnets.
  • Each subnet gets the remaining 6 host bits: 2^6 = 64 addresses per subnet.
  • Two addresses in each subnet are reserved (the network address and the broadcast address), so each subnet has 62 usable host addresses.
  • The new prefix length is /26 (24 original + 2 borrowed = 26). The subnet mask for a /26 is 255.255.255.192.

Why borrow 2 bits specifically?

You need 3 subnets (one per department). Borrowing 1 bit only gives 2 subnets. Borrowing 2 bits gives 4 subnets. Since 4 is the smallest power of 2 that's greater than or equal to 3, borrowing 2 bits is the right choice.

The 4th subnet (192.168.1.192/26) stays unused for now. You'll use it in the Secret Mission later.

Calculate your 3 subnet ranges

Each subnet starts where the previous one ends. Since each /26 contains 64 addresses, the subnets start at addresses 0, 64, and 128.

  • Open a text file or grab a piece of paper. Write out the following subnet plan:
=== SUBNET PLAN ===

Subnet 1 (Sales)
  Network address:   192.168.1.0/26
  Usable host range: 192.168.1.1 - 192.168.1.62
  Broadcast address: 192.168.1.63
  Subnet mask:       255.255.255.192

Subnet 2 (Engineering)
  Network address:   192.168.1.64/26
  Usable host range: 192.168.1.65 - 192.168.1.126
  Broadcast address: 192.168.1.127
  Subnet mask:       255.255.255.192

Subnet 3 (HR)
  Network address:   192.168.1.128/26
  Usable host range: 192.168.1.129 - 192.168.1.190
  Broadcast address: 192.168.1.191
  Subnet mask:       255.255.255.192

What do these addresses mean?

  • Network address is the ID of the subnet itself. No device uses this address.
  • Usable host range is the pool of addresses you can assign to devices (router interfaces, PCs, servers).
  • Broadcast address is used to send a message to every device on the subnet at once. No device uses this address either.
  • Subnet mask (255.255.255.192) tells devices which bits are the network portion and which are the host portion. It's the dotted-decimal form of /26.

What is CIDR notation?

The /26 after an IP address is called CIDR notation. It tells you how many bits in the address are used for the network portion. A /26 means the first 26 bits are locked (the network ID) and the remaining 6 bits identify individual hosts.

Assign specific addresses to each device

Now that you have your subnet ranges, decide which specific IP goes to which device. A common convention is to give the router the first usable address on each subnet.

Why does the router get the first address?

The router is the default gateway for every device on the subnet. It's the exit door that traffic uses to reach other subnets. Giving it the first usable address (.1, .65, .129) makes the network easier to remember and troubleshoot.

  • Add the following device assignments to your subnet plan:
=== DEVICE ADDRESS ASSIGNMENTS ===

Router Interfaces (default gateway for each subnet):
  GigabitEthernet0/0 (Sales):       192.168.1.1
  GigabitEthernet0/1 (Engineering):  192.168.1.65
  GigabitEthernet0/2 (HR):           192.168.1.129

PC Addresses:
  Sales-PC1:  192.168.1.2    (gateway: 192.168.1.1)
  Sales-PC2:  192.168.1.3    (gateway: 192.168.1.1)
  Eng-PC1:    192.168.1.66   (gateway: 192.168.1.65)
  Eng-PC2:    192.168.1.67   (gateway: 192.168.1.65)
  HR-PC1:     192.168.1.130  (gateway: 192.168.1.129)
  HR-PC2:     192.168.1.131  (gateway: 192.168.1.129)

All devices use subnet mask: 255.255.255.192

What does this table tell us?

  • The router has one interface (one IP address) on each subnet. This is how it connects the three departments together.
  • Each PC's gateway points to the router interface on its own subnet. When a PC wants to reach a different department, it sends traffic to this gateway address.
  • Every device shares the same subnet mask (255.255.255.192) because all subnets are the same /26 size.
  • Double-check that your plan has all three subnets and all device assignments written out completely.
  • Verify that no two devices share the same IP address and that every address falls within its subnet's usable host range.

Not sure your math is right?

  • Each subnet boundary is always a multiple of the block size. For /26, the block size is 64. So subnets start at .0, .64, .128, and .192.
  • The broadcast address is always one less than the next subnet's network address. Subnet 1's broadcast is .63 because Subnet 2 starts at .64.
  • If an address like 192.168.1.64 looks like it should be usable, remember that .64 is the network address of Subnet 2. The first usable host is .65.

Help me understand why my subnet boundaries are wrong.

✔️ Awesome, I've got everything!

Great. Make sure you've saved your subnet plan. You'll reference it constantly in the next steps when configuring devices.

ⓧ I'd like to double check the full plan

Here's the complete subnet plan with all addresses. Compare yours against this:

=== COMPLETE SUBNET PLAN ===

Subnet 1 (Sales)
  Network address:   192.168.1.0/26
  Usable host range: 192.168.1.1 - 192.168.1.62
  Broadcast address: 192.168.1.63
  Subnet mask:       255.255.255.192
  Router interface:  192.168.1.1 (GigabitEthernet0/0)

Subnet 2 (Engineering)
  Network address:   192.168.1.64/26
  Usable host range: 192.168.1.65 - 192.168.1.126
  Broadcast address: 192.168.1.127
  Subnet mask:       255.255.255.192
  Router interface:  192.168.1.65 (GigabitEthernet0/1)

Subnet 3 (HR)
  Network address:   192.168.1.128/26
  Usable host range: 192.168.1.129 - 192.168.1.190
  Broadcast address: 192.168.1.191
  Subnet mask:       255.255.255.192
  Router interface:  192.168.1.129 (GigabitEthernet0/2)

=== DEVICE ADDRESS ASSIGNMENTS ===

Router Interfaces (default gateway for each subnet):
  GigabitEthernet0/0 (Sales):       192.168.1.1
  GigabitEthernet0/1 (Engineering):  192.168.1.65
  GigabitEthernet0/2 (HR):           192.168.1.129

PC Addresses:
  Sales-PC1:  192.168.1.2    (gateway: 192.168.1.1)
  Sales-PC2:  192.168.1.3    (gateway: 192.168.1.1)
  Eng-PC1:    192.168.1.66   (gateway: 192.168.1.65)
  Eng-PC2:    192.168.1.67   (gateway: 192.168.1.65)
  HR-PC1:     192.168.1.130  (gateway: 192.168.1.129)
  HR-PC2:     192.168.1.131  (gateway: 192.168.1.129)

All devices use subnet mask: 255.255.255.192

Your addressing plan is locked in. Next up, you'll build the physical network topology in Packet Tracer and connect all your devices with cables.

Build the Physical Topology

You have a complete subnet plan ready to go. Now it is time to bring that plan to life inside Cisco Packet Tracer.

Every network starts with physical devices and cables. In this step, you will place a router, switches, and PCs into the workspace, cable them together, and label everything so your topology is easy to read.

In this step, get ready to:
  • Add a router, three switches, and six PCs to the Packet Tracer workspace.
  • Cable all devices together using copper straight-through connections.
  • Rename and label every device and subnet for clarity.
Add devices to the workspace

Your network needs three types of devices: a router to forward traffic between subnets, a switch for each department, and two PCs per department to represent end users.

  • Look at the bottom-left corner of the Packet Tracer window. This is the Device-Type Selection panel where you pick device categories.
  • Click the Routers category icon.
  • In the device list that appears to the right, find and click 2911.
  • Click in the center of the workspace to place the router.

Why the 2911?

The Cisco 2911 is the standard router used in CCNA Packet Tracer labs. It comes with exactly three GigabitEthernet interfaces (GigabitEthernet0/0, GigabitEthernet0/1, GigabitEthernet0/2), which perfectly matches your 3-subnet design.

  • Click the Switches category icon in the bottom-left panel.
  • Select 2960 from the device list.
  • Click in the workspace to place the first switch to the left of the router.
  • Place a second 2960 switch below the router.
  • Place a third 2960 switch to the right of the router.
  • Click the End Devices category icon in the bottom-left panel.
  • Select PC from the device list.
  • Place two PCs near each switch (six PCs total, two per department).

Your workspace should now have 10 devices: one router in the center, three switches branching out from it, and two PCs near each switch.

Don't see the 2911 or 2960 in the list?

Make sure you clicked the correct category icon first (Routers or Switches). The device list to the right updates based on which category is selected. Hover over the category icons to see their names in a tooltip.

Help me find the 2911 router or 2960 switch in Packet Tracer

Cable the devices

With all devices placed, you need to connect them with cables. Every connection in this lab uses a Copper Straight-Through cable, which is the standard cable type for connecting switches to routers and PCs to switches.

  • Click the Connections icon (the lightning bolt) in the bottom-left panel.
  • Select Copper Straight-Through from the cable options that appear.

Now connect each switch to the router. You will click one device, select a port, then click the second device and select a port.

  • Click on Switch0 (the first switch you placed).
  • Select GigabitEthernet0/1 from the port list that appears.
  • Click on the router (Router0).
  • Select GigabitEthernet0/0 from the router's port list. This connects the Sales switch to the router.
  • Click on Switch1 (your second switch).
  • Select GigabitEthernet0/1 from the port list.
  • Click on the router.
  • Select GigabitEthernet0/1 from the router's port list. This connects the Engineering switch to the router.
  • Click on Switch2 (your third switch).
  • Select GigabitEthernet0/1 from the port list.
  • Click on the router.
  • Select GigabitEthernet0/2 from the router's port list. This connects the HR switch to the router.

Which port on the switch?

On the switch side, you can use any available port. GigabitEthernet0/1 is a clean choice for the uplink to the router. On the router side, the specific port matters because your subnet plan maps each interface to a department.

Now connect the PCs to their respective switches using the same Copper Straight-Through cable type.

  • Click on the first PC near Switch0.
  • Select FastEthernet0 from the PC's port list.
  • Click on Switch0.
  • Select any available FastEthernet port (for example, FastEthernet0/1).
  • Repeat for the second PC near Switch0, connecting it to a different FastEthernet port on the same switch.
  • Repeat the same process for the two PCs near Switch1, and the two PCs near Switch2.

After cabling, you will see colored dots (link lights) on each connection. They start amber and turn green within a few seconds. Green means physical connectivity is established.

Link lights staying red or not appearing?

A red light means the cable type is wrong for that connection. Make sure you selected Copper Straight-Through (not Crossover or Serial). Delete the incorrect cable by clicking the Delete tool (the X icon in the toolbar), clicking the bad cable, then re-cable with the correct type.

If lights are amber, wait 30-60 seconds. Switches take time to move from listening/learning states to forwarding.

Help me troubleshoot my cable connections

Label the topology

Default names like "Router0" and "PC0" make it hard to tell which device belongs to which department. Renaming everything now saves confusion for the rest of the project.

  • Click the router icon on the workspace to open its configuration window.
  • Select the Config tab.
  • In the Display Name field, type HQ-Router and press Enter.
  • Close the configuration window.
  • Click Switch0 to open its configuration window.
  • Select the Config tab and change the Display Name to Sales-SW.
  • Rename Switch1 to Eng-SW using the same process.
  • Rename Switch2 to HR-SW.
  • Click the first PC near Sales-SW to open its configuration window.
  • Select the Config tab and change the Display Name to Sales-PC1.
  • Rename the remaining PCs: Sales-PC2, Eng-PC1, Eng-PC2, HR-PC1, HR-PC2.

What is the Display Name field?

The Display Name controls the label shown below each device icon on the workspace. Changing it does not affect the device's internal hostname (which you configure via CLI). It is purely a visual label to keep your topology readable.

Finally, add text notes to label each subnet area on the workspace.

  • Click the Place Note tool in the Common Tools Bar at the top of the workspace (you can also press the N key as a shortcut).
  • Click on the workspace near Sales-SW and its PCs.
  • A text box appears. Type Sales Subnet: 192.168.1.0/26 and click elsewhere to place the note.
  • Repeat to add a note near Eng-SW: Engineering Subnet: 192.168.1.64/26.
  • Add a third note near HR-SW: HR Subnet: 192.168.1.128/26.
  • Click the Select tool (the arrow icon in the top-left of the toolbar) to exit note-placing mode.
  • Save your work by pressing Ctrl+S (Windows) or Cmd+S (macOS).
  • Name the file something memorable like office-network.pkt and save it to your Desktop.

All link lights should now be green across your topology, confirming physical connectivity between every device.

Some lights still amber after a minute?

Switch ports go through Spanning Tree Protocol states before reaching forwarding mode. This takes around 30 seconds. If lights are still amber after a full minute, try clicking the Fast Forward Time button (the double-arrow icon next to the clock in the bottom-right) to advance the simulation clock.

Help me get my switch lights to turn green

Your physical topology is complete. Every device is placed, cabled, and clearly labeled. Next up, you will configure the router interfaces via the CLI to bring your subnet plan to life at Layer 3.

Configure the Router Interfaces

Your topology is physically wired and labeled. Every link light is green, meaning the cables are working at Layer 1. But the router still has no idea which subnet lives on which port.

In this step, you'll bring the router online by configuring IP addresses on each of its three GigabitEthernet interfaces using the Cisco IOS command line. This is where your subnet plan from Step 1 becomes real network configuration.

In this step, get ready to:
  • Access the router's CLI and enter global configuration mode.
  • Configure IP addresses on all three GigabitEthernet interfaces.
  • Verify all interfaces are up with the correct addresses.
Access the router CLI

Before you can configure anything, you need to reach the router's command line interface inside Packet Tracer.

  • Click on HQ-Router in your topology to open its properties window.
  • Click the CLI tab at the top of the window.
  • Press Enter to get a command prompt.
  • Enter privileged exec mode and then global configuration mode by typing these commands:
enable
configure terminal

What do these commands do?

  • enable moves you from user exec mode (the basic read-only mode) into privileged exec mode. This gives you access to all show commands and the ability to enter configuration mode.
  • configure terminal enters global configuration mode, where you can make changes to the router's running configuration.

Your prompt should now show Router(config)# indicating you are in global configuration mode.

Still seeing Router> instead of Router(config)#?

If your prompt shows Router> you are still in user exec mode. Type enable first to get to Router#, then type configure terminal to reach Router(config)#.

If the router asks whether to enter the initial configuration dialog, type no and press Enter.

Help me get into global configuration mode on my router.

Configure all three GigabitEthernet interfaces

Each router interface acts as the default gateway for its subnet. You'll assign the first usable IP address from each subnet to the corresponding interface and bring it online.

  • Configure GigabitEthernet0/0 for the Sales subnet by typing these commands:
interface GigabitEthernet 0/0
ip address 192.168.1.1 255.255.255.192
no shutdown
exit

What does this code do?

  • interface GigabitEthernet 0/0 enters interface configuration mode for the specific port connected to Sales-SW.
  • ip address 192.168.1.1 255.255.255.192 assigns the first usable IP from Subnet 1 (192.168.1.0/26) and sets the /26 subnet mask.
  • no shutdown brings the interface up. Router interfaces are administratively down by default, so you must explicitly enable them.
  • exit returns you to global configuration mode so you can configure the next interface.
  • Configure GigabitEthernet0/1 for the Engineering subnet by typing these commands:
interface GigabitEthernet 0/1
ip address 192.168.1.65 255.255.255.192
no shutdown
exit

What does this configure?

This assigns the first usable IP from Subnet 2 (192.168.1.64/26) to the port connected to Eng-SW. The no shutdown command brings it online.

  • Configure GigabitEthernet0/2 for the HR subnet by typing these commands:
interface GigabitEthernet 0/2
ip address 192.168.1.129 255.255.255.192
no shutdown
exit

What does this configure?

This assigns the first usable IP from Subnet 3 (192.168.1.128/26) to the port connected to HR-SW. All three interfaces are now configured and active.

Why does the router get the first usable IP?

It is a common convention to assign the first (or last) usable host address to the default gateway. This makes it easy to remember and troubleshoot. Every PC on the subnet will point to this address as its way out to other networks.

Seeing an 'Invalid input detected' error?

Double check you are in global configuration mode (prompt shows Router(config)#) before typing the interface command. If your prompt shows Router# instead, type configure terminal first.

Also verify you typed the interface name exactly as shown, including the space between GigabitEthernet and 0/0.

Help me fix an invalid input error on my router interface command.

Verify the configuration

Now confirm all three interfaces are up and have the correct IP addresses assigned.

  • Exit configuration mode and check your interfaces by typing these commands:
end
show ip interface brief

What does this command show?

end exits all configuration modes and returns you to privileged exec mode (Router#).

show ip interface brief displays a table of all interfaces with their IP addresses, status, and protocol state. You need to see all three GigabitEthernet interfaces showing "up" in both the Status and Protocol columns.

You should see output similar to this:

Interface              IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0     192.168.1.1     YES manual up                    up
GigabitEthernet0/1     192.168.1.65    YES manual up                    up
GigabitEthernet0/2     192.168.1.129   YES manual up                    up
  • Confirm all three interfaces show up under both the Status and Protocol columns.
  • Confirm the IP addresses match your subnet plan: 192.168.1.1, 192.168.1.65, and 192.168.1.129.

An interface shows 'administratively down'?

This means the no shutdown command was not applied to that interface. Go back into configuration mode by typing configure terminal, then enter the specific interface (e.g. interface GigabitEthernet 0/0) and type no shutdown.

Help me bring my router interface up.

✔️ Awesome, I've got everything!

Great. All three interfaces are configured and active. Your router is ready to forward traffic between subnets.

ⓧ I'd like to double check the full commands

Here are all the commands from this step in sequence:

enable
configure terminal
interface GigabitEthernet 0/0
ip address 192.168.1.1 255.255.255.192
no shutdown
exit
interface GigabitEthernet 0/1
ip address 192.168.1.65 255.255.255.192
no shutdown
exit
interface GigabitEthernet 0/2
ip address 192.168.1.129 255.255.255.192
no shutdown
exit
end
show ip interface brief

Your router is now configured and ready to forward packets between all three subnets. Next up, you'll configure the PCs with their IP addresses and test whether traffic can flow across the entire network.

Configure PCs and Verify Connectivity

Your router is configured and all three interfaces are up. The router is ready to forward traffic between subnets.

Now you need to configure the end devices. Each PC needs to know its own IP address, which subnet it belongs to, and where to send traffic destined for other subnets. That "where to send" address is the default gateway.

In this step, get ready to:
  • Configure IP addresses, subnet masks, and default gateways on all 6 PCs.
  • Verify same-subnet connectivity by pinging between PCs on the Sales network.
  • Confirm cross-subnet routing by pinging PCs in different departments.
Configure each PC's IP settings

Each PC needs three values: an IP address, a subnet mask, and a default gateway. The subnet mask tells the PC which addresses are "local" (on its own subnet). The default gateway is the router interface IP for that subnet.

You will configure Sales-PC1 first, then repeat the same process for the other 5 PCs using the addressing table below.

  • Click on Sales-PC1 in the workspace to open its configuration window.
  • Click the Desktop tab at the top of the window.
  • Click IP Configuration.
  • In the IP Address field, enter 192.168.1.2.
  • In the Subnet Mask field, enter 255.255.255.192.
  • In the Default Gateway field, enter 192.168.1.1.
  • Close the Sales-PC1 configuration window.

Why 255.255.255.192?

The subnet mask 255.255.255.192 is the decimal form of a /26 prefix. It tells the PC that the first 26 bits are the network portion. Only addresses within the same /26 block are considered "local" traffic.

Anything outside that range gets forwarded to the default gateway (the router), which handles delivery to the correct subnet.

Now repeat the same process for the remaining 5 PCs. Use the addressing table below for each device:

  • Sales-PC2: IP 192.168.1.3, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.1.
  • Eng-PC1: IP 192.168.1.66, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.65.
  • Eng-PC2: IP 192.168.1.67, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.65.
  • HR-PC1: IP 192.168.1.130, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.129.
  • HR-PC2: IP 192.168.1.131, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.129.

Speed up the process

You can leave multiple PC configuration windows open at the same time. Click each PC in the workspace, go to Desktop > IP Configuration, fill in the values, then move to the next. The settings save automatically as you type.

Not sure which gateway to use?

The default gateway for each PC is always the router's interface IP on that same subnet. Sales PCs use 192.168.1.1 (GigabitEthernet0/0). Engineering PCs use 192.168.1.65 (GigabitEthernet0/1). HR PCs use 192.168.1.129 (GigabitEthernet0/2).

help me figure out the correct default gateway for my PC

Test within the same subnet

Before testing across subnets, confirm that PCs on the same subnet can talk to each other through the switch. This proves Layer 2 connectivity is working.

  • Click on Sales-PC1 to open its configuration window.
  • Click the Desktop tab.
  • Click Command Prompt.
  • Ping Sales-PC2 by typing the following command and pressing Enter:
ping 192.168.1.3

You should see 4 reply lines with round-trip times, confirming that Sales-PC1 can reach Sales-PC2 through Sales-SW.

What does this prove?

Both PCs are on the same /26 subnet (192.168.1.0/26). The ping travels from Sales-PC1 to Sales-SW and then to Sales-PC2. It never touches the router because both devices share the same network.

If this ping succeeds, your IP addresses and subnet masks are correct for the Sales department.

Seeing Request timed out?

Double-check that Sales-PC2 has IP address 192.168.1.3 and subnet mask 255.255.255.192. A wrong subnet mask (like 255.255.255.0) is a common mistake. Also verify the link light between Sales-PC2 and Sales-SW is green.

help me troubleshoot why my same-subnet ping is failing in Packet Tracer

Test across subnets

The real test of your network is whether PCs in different departments can communicate. Cross-subnet traffic must travel through the router, proving that your router configuration and default gateways are all correct.

  • In the same Command Prompt on Sales-PC1, ping Eng-PC1 by running:
ping 192.168.1.66
  • Next, ping HR-PC1 by running:
ping 192.168.1.130

You should see successful replies from both commands. If the first ping in a sequence shows "Request timed out" but the remaining three succeed, that is normal.

Why does the first ping sometimes time out?

The first packet triggers an ARP request. ARP resolves IP addresses to MAC addresses. While the network figures out the MAC address of the next hop, the first ICMP packet may expire.

Subsequent pings succeed because the MAC address is now cached. This is normal behavior in both Packet Tracer and real networks.

Now use Simulation Mode to visualize the exact path your packet takes across the network.

  • Click the Simulation tab in the bottom-right corner of the Packet Tracer window (the stopwatch icon, partially hidden behind the Realtime tab).
  • Click Edit Filters in the Simulation Panel. Click Show All/None to deselect everything, then select only ICMP under the IPv4 tab.
  • Click the Add Simple PDU icon (closed envelope) in the right toolbar.
  • Click Sales-PC1 as the source, then click Eng-PC1 as the destination.
  • Click Capture / Forward repeatedly to step through each hop.

Watch the packet travel from Sales-PC1 to Sales-SW, then to HQ-Router, then to Eng-SW, and finally to Eng-PC1. This is inter-subnet routing in action.

What is Simulation Mode showing you?

Simulation Mode lets you freeze time and step through network events one by one. Each click of Capture / Forward advances the packet by one hop.

You can see the packet leave the source PC, pass through the switch, arrive at the router (which reads the destination IP and forwards it out the correct interface), pass through the destination switch, and arrive at the destination PC. This is exactly how real routers forward traffic between subnets.

  • Switch back to Realtime mode by clicking the Realtime tab in the bottom-right corner.
  • Save your topology by clicking File in the top menu bar, then Save As.
  • Choose a location and name for your file. The file type defaults to .pkt.
  • Click Save.

Cross-subnet ping failing completely?

If all 4 pings time out (not just the first one), check these common causes:

  • Verify the default gateway on your source PC matches the router's interface IP for that subnet.
  • Confirm all three router interfaces still show "up" status. Click HQ-Router, go to the CLI tab, and run show ip interface brief.
  • Check that the destination PC's subnet mask is 255.255.255.192, not 255.255.255.0. A mismatched mask breaks routing.

help me debug why my cross-subnet ping is failing in Packet Tracer

✔️ Awesome, I've got everything!

Great. Double check that all 6 PCs have the correct IP, mask, and gateway by clicking each one and viewing Desktop > IP Configuration.

ⓧ I'd like to double check all the PC settings

Here is the complete addressing table for all 6 PCs:

  • Sales-PC1: IP 192.168.1.2, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.1.
  • Sales-PC2: IP 192.168.1.3, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.1.
  • Eng-PC1: IP 192.168.1.66, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.65.
  • Eng-PC2: IP 192.168.1.67, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.65.
  • HR-PC1: IP 192.168.1.130, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.129.
  • HR-PC2: IP 192.168.1.131, Subnet Mask 255.255.255.192, Default Gateway 192.168.1.129.

Secret mission

Add a 4th Department with VLSM

The company just acquired a small Security team of 5 people. Instead of wasting a full /26 subnet (62 addresses) on just 5 hosts, can you use Variable Length Subnet Masking to carve a right-sized subnet from your unused address space?

Clean Up Your Resources

Clean Up Your Resources

This project runs entirely locally in Cisco Packet Tracer, so there are no ongoing costs or cloud resources to worry about.

Decide whether to keep your topology file for future practice, or delete it to start fresh.

Resources you used:

  • Packet Tracer topology file (.pkt file saved locally).
  • Subnet plan (text file or handwritten notes).

Keep everything running

No action needed. Choose this if you want to keep practicing subnetting or expand the topology further.

  • Your .pkt file stays where you saved it. You can reopen it in Packet Tracer any time.
  • Your subnet plan is useful reference material for future CCNA study.

Pause - I'll come back to this later

Close Packet Tracer to free up system memory. Your saved topology file remains on disk for when you return.

  • Save your topology one final time by pressing Cmd+S (macOS) or Ctrl+S (Windows).
  • Close Cisco Packet Tracer.
  • Your .pkt file and subnet plan remain on your computer, ready to reopen.

Delete - I don't want to use this again

Remove the project files from your computer entirely.

  • Close Cisco Packet Tracer if it is still open.
  • Delete your .pkt topology file. Locate it in Finder (macOS) or File Explorer (Windows), right-click the file, and select Move to Trash (macOS) or Delete (Windows).
  • Delete your subnet plan text file the same way, if you saved one.
  • Empty your Trash or Recycle Bin to permanently remove the files.

What about Cisco Packet Tracer itself?

Packet Tracer is free and useful for future networking practice. There is no reason to uninstall it unless you need the disk space.

Nice Work!

Nice Work!

Nice work! You just built a fully functional multi-subnet office network from scratch, starting with nothing but a /24 address block and ending with cross-department connectivity verified through ping.

You learned how to:

  • Calculate IPv4 subnets by hand, dividing 192.168.1.0/24 into three /26 subnets with correct network addresses, host ranges, and broadcast addresses.
  • Build a multi-subnet office topology in Cisco Packet Tracer with a 2911 router, three 2960 switches, and six PCs wired with straight-through cables.
  • Configure Cisco IOS router interfaces via CLI using enable, configure terminal, ip address, and no shutdown, then verify connectivity with show ip interface brief and ping.
  • Secret Mission: Used VLSM to add a 4th department with a right-sized /28 subnet, proving you can design efficient addressing plans that allocate only the space each department needs.

Ready to quiz yourself?