1. What Is DHCP?

DHCP stands for Dynamic Host Configuration Protocol. It automatically provides network configuration information to devices such as computers, laptops, and printers.

Instead of manually configuring an IP address on every device, a DHCP server can assign the required settings automatically.

What Information Does DHCP Provide?

• IP address
• Subnet mask
• Default gateway
• DNS server address
• IP address lease duration

2. How Does DHCP Work?

DHCP commonly uses a four-step process known as DORA.

1. Discover: The client broadcasts a message to find a DHCP server.
2. Offer: The DHCP server offers an available IP address.
3. Request: The client requests the offered IP address.
4. Acknowledge: The server confirms the address assignment.

Client                 DHCP Server
  |                         |
  |---- DHCP Discover ----->|
  |<----- DHCP Offer -------|
  |---- DHCP Request ------>|
  |<--- DHCP Acknowledge ---|
  |                         |
  IP configuration received
    

3. Lab Requirements

• Cisco Packet Tracer
• 1 Cisco router (for example, 2911)
• 1 Cisco 2960 switch
• 1 Server-PT device
• 3 PCs
• Copper straight-through cables

4. Network Topology

In this lab, the router connects the LAN to the network, while a dedicated server provides DHCP services to the PCs.

              Router R1
             192.168.10.1
                  |
                  |
               Switch
              /  |  \
             /   |   \
           PC1  PC2  PC3
                  |
              Server-PT
             192.168.10.2
    

All devices are connected to the same LAN. The server will provide IP configuration to the client PCs.

5. IP Addressing Plan

DHCP pool: 192.168.10.100 – 192.168.10.150

6. Step 1 – Build the Topology

1. Open Cisco Packet Tracer.
2. Add one router, one switch, one Server-PT, and three PCs.
3. Connect the router to the switch.
4. Connect the server and all three PCs to the switch.
5. Wait until the link indicators become green.

7. Step 2 – Configure the Router

Open the router CLI and configure its LAN interface.

enable
configure terminal

interface gigabitEthernet 0/0
ip address 192.168.10.1 255.255.255.0
no shutdown
exit

end
    

This router interface acts as the default gateway for the LAN.

Note: Interface names depend on the router model selected in Packet Tracer.

8. Step 3 – Configure the DHCP Server's Static IP

Click Server-PT and follow these steps:

1. Open the Desktop tab.
2. Select IP Configuration.
3. Choose Static.
4. Enter the following values:

The server uses a static IP address so clients can consistently reach the DHCP service.

9. Step 4 – Enable DHCP Service

Now configure the DHCP pool on the server.

1. Click Server-PT.
2. Open the Services tab.
3. Select DHCP.
4. Set the DHCP service to On.
5. Enter the pool configuration below.

Click Add or Save, depending on the Packet Tracer version, to create the pool.

The server will assign client addresses from 192.168.10.100 through 192.168.10.150.

10. Step 5 – Configure the PCs to Use DHCP

Repeat these steps for PC1, PC2, and PC3:

1. Click the PC.
2. Open the Desktop tab.
3. Select IP Configuration.
4. Click DHCP.
5. Wait for the IP configuration to appear.

Each PC should receive an IP address from the configured DHCP pool, along with its subnet mask, default gateway, and DNS server.

11. Step 6 – Verify the IP Configuration

Open the PC command prompt and enter:

ipconfig
    

Example output for PC1:

IP Address:      192.168.10.100
Subnet Mask:     255.255.255.0
Default Gateway: 192.168.10.1
    

Other PCs should receive different available addresses from the pool. The exact assignment order may vary.

12. Step 7 – Test Network Connectivity

From PC1, ping the DHCP server:

ping 192.168.10.2
    

Next, ping the router:

ping 192.168.10.1
    

You can also ping PC2 using its assigned IP address. Successful replies confirm connectivity between devices on the LAN.

13. DHCP Troubleshooting

14. Important DHCP Ports

DHCP uses UDP for communication:

• UDP 67: DHCP server port.
• UDP 68: DHCP client port.

When clients and servers are on different IP subnets, a DHCP relay agent (commonly configured with Cisco's ip helper-address) is needed to forward DHCP requests to a remote server.

15. Frequently Asked Questions

16. Practice Challenge

Now try these tasks:

1. Add two more PCs to the network.
2. Configure the DHCP pool to support more clients.
3. Verify that every PC receives a unique IP address.
4. Change the DNS server setting in the DHCP pool.
5. Test connectivity between all PCs.

Conclusion

In this Packet Tracer lab, you learned how to build a DHCP server, configure a static IP address for the server, create a DHCP pool, and automatically assign IP addresses to client devices.

Understanding DHCP is essential for managing real-world networks because it reduces manual configuration and makes IP address management easier.

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