Dynamic Host Configuration Protocol (DHCP) is an interactive client-server protocol that automatically provides a host (PC, Laptop, Phone, etc) with an Internet Protocol (IP) address upon request. The purpose of this activity is for learners to see DHCP in action rather than just read about the DHCP handshake theory. A secondary purpose is to have learners experience frustration when hosts do not receive a DHCP IP address. Learners can see how the packets move and where they may get hung up while working to ensure DHCP functions correctly on their network. Finally, learners can see Address Resolution Protocol (ARP) in action. While DHCP occurs when a host requests an IP address for an existing MAC address, ARP occurs when a host has an IP address but is unsure what MAC address it belongs to.

We strongly recommend you complete the DHCP-Linux lab first. Since this is essentially the DHCP-Linux lab, but using a different Linux distribution, these steps are somewhat abbreviated. It is assumed that you are already familiar with the DHCP-Linux lab. If you follow these steps exactly, you will create an Alpine Linux DHCP server, but your understanding will be limited. Alpine Linux is much lighter than Ubuntu Server, which helps address performance issues. Alpine Linux is terminal-only. Proceed with caution, as incorrect commands and incorrectly edited configuration files can break your VM!

Estimated time for completion: 60 minutes

LEARNING OBJECTIVES

• Successfully deploy a DHCP solution using Alpine Linux on an enterprise network
• Capture and Observe DHCP packets using Wireshark
• Capture and Observe ARP packets using Wireshark
• Successfully add hosts to an enterprise network and receive IP addresses automatically

PREREQUISITES

• A GNS3 environment
• Alpine Linux VM

DELIVERABLES

• 5 Screenshots:
  • Wireshark – DHCP Packets for PC1
  • Wireshark – DHCP Packets for PC2
  • Wireshark – ARP Packets for PC1/PC2
  • GNS3 Workspace
  • Configuration of the DHCP Daemon

RESOURCES

• Kea Documentation 
• Internet Systems Consortium – “Kea Administrator Reference Manual”

CONTRIBUTORS AND TESTERS

• Antionette Hults, Cybersecurity Student, ERAU-Prescott
• Mathew J. Heath Van Horn, PhD

Phase I – Create the DHCP server vm

 

1. Open Oracle VirtualBox
2. Right-click on your Alpine VM and click Clone
   1. In the Name field type “DHCP-Alpine”
   2. Under clone type, select “Full Clone”
   3. Under MAC Address Policy, select “Generate new MAC address for all network adapters”
3. Select DHCP-Alpine and start the VM
4. Log in with the same credentials you used to create the original Alpine VM. In our example, we used:
   1. Username: root
   2. Password: toor
5. Use the command line to install two packages using the command below

1. Go to the kea config directory by typing the command

   cd /etc/kea

    

   Command	Purpose
   cd	Change Directory – a built-in shell tool used to navigate through files and folders
   /etc/kea	Change working directory to the kea subfolder of the etc folder.  The (et cetera) folder is the nerve center of a Linux system. It stores all system-wide configuration files.

   
2. Once in the directory, backup the kea-dhcp4.conf and delete the original one by running the following commands

   1. cp kea-dhcp4.conf kea-dhcp4.bak

      cp is the Linux command for “copy”

   2. rm kea-dhcp4.conf

      rm is the Linux command for “remove”

3. Download the new kea-dhcp4.conf by typing the command

   curl -O https://raw.githubusercontent.com/braedyncase06/MasteringEnterpriseNetworks/main/Alpine-kea-configs/kea-dhcp4.conf

   NOTE: The dash is not followed by a zero; it is followed by an O as in Oscar. Also, the link must be perfectly copied for this command to work. Because Alpine Linux is so minimal, there is no copy and paste function between your computer and the VM terminal. So take your time entering the above command, or you will have to redo it!

    

4. Verify that the download was successful by typing the command

   cat kea-dhcp4.conf

    

5. The contents of the file should match the following image
   

   

    

6. If the contents DO NOT match the picture above, go back to step 3 and ensure that you type in the link correctly.

   NOTE: You can manually adjust the Kea IPv4 configuration file by following the instructions in the DHCP-Linux chapter.

1. Run the command

   vi /etc/network/interfaces

2. In the text editor, scroll down to the last line that contains “iface eth0 inet dhcp”
3. Press “i” to edit the file
4. Remove the dhcp part at the end of the line
5. type in “static”
6. The line should now read “iface eth0 inet static”
7. Press Enter to go to the blank line beneath and press Tab
8.  In the newly indented line type “address 200.200.200.254”
9. Press Enter to make a new line and press Tab
10. In the newly indented line type “netmask 255.255.255.0”
11. Press Enter to make a new line and press Tab
12. In the newly indented line type “gateway 200.200.200.1”
13. The file should look like the following image
    

    

14. Press Escape to stop editing the file
15. Then type in “:wq” to save changes and exit out of the text editor
16. Type the following command to activate kea dhcp server upon boot

    rc-update add kea-dhcp4 default

     

    Command	Use
    rc-update	A utility used to manage which services start automatically at boot
    add	Add the following service to the rc-update utility
    kea-dhcp4	The file we just edited using vi
    deafult	Start normal operational services after

17. Power down the VM

1. Open GNS3
2. Wait for the GNS3 VM to connect and for the status indicator to turn green
3. Create a new project by going to File > New Blank Project
   

   

4. Name the project whatever you want (Mine is called DHCP-Alpine)
5.  To add the VM, go to the top of the window, click on Edit > Preferences > VirtualBox VMs
   

   

6.  Click on New
7. In the Window, select Run this VirtualBox VM on my local computer
8. Click Next
9. In the next window, click the dropdown arrow and select the name of your Alpine DHCP VM that you made
10. Click Finish
    

    

11.  In the GNS3 project window, go to Browse End Devices (Desktop Computer Icon at the left of the window)
12. Double-click on the VM you added
13.  In the configuration window, click on Network
14. At the bottom of the window, check the box next to Allow GNS3 to use any configured VirtualBox adapter
    

    

     

15. Click OK
16. Drag DHCP-Alpine into the project space
17. Drag VPCS into the project space
18. When the pop-up window opens, click the dropdown arrow and select GNS3 VM
19. Click OK
20. Drag another VPCS into the project space
21.  When the pop-up window opens, click the dropdown arrow and select GNS3 VM
22. Click OK
23. Go to Switches (just above Browse End Devices)
24. Drag the Ethernet Switch into the project space
25. When the pop-up window opens, click the dropdown arrow and select GNS3 VM
26. To the left of the window, click on the wire icon
27.  Click on DHCP-Alpine-1 and select Ethernet0, then click on Switch1 and select Ethernet0
28. Click on PC1 and select Ethernet0 then click on Switch1 and select Ethernet1
29. Click on PC2 and select Ethernet0 then click on Switch1 and select Ethernet2
    

    

1. At the top of the window, press the start button
2. After all devices start fully (indicator at the right is green), right-click on the wire between PC1 and Switch1
3. Click Start Capture
4. In the pop-up window, click OK
5. Go back to the GNS3 Project window and right-click on PC1
6. Click Console
7. In the console, type the command

   ip dhcp

    

8. You should see DORA printed on the terminal, indicating that you have successfully connected to your DHCP server!
   

   

    

9. You should also see a full DHCP handshake in your Wireshark capture
   

   

   10. Repeat with PC2 and then try to ping PC1 with the newly assigned IP addresses

Career Connection

Automated network services such as DHCP are essential to modern enterprise operations, and many organizations deploy these services on lightweight Linux platforms to improve efficiency and simplify administration. Network engineers, systems administrators, and cybersecurity professionals routinely configure, monitor, and troubleshoot DHCP services while validating network behavior with packet analysis tools such as Wireshark. The combination of Linux command-line administration, protocol analysis, and troubleshooting practiced in this chapter reflects the day-to-day responsibilities of professionals responsible for maintaining reliable enterprise network infrastructure.

End of Lab