Enable Integrated DHCP Feature in Dnsmasq and Configure DHCP Server on AlmaLinux

Introduction

Dnsmasq is a lightweight, versatile tool commonly used for DNS caching and as a DHCP server. It is widely adopted in small to medium-sized network environments because of its simplicity and efficiency. AlmaLinux, an enterprise-grade Linux distribution derived from Red Hat Enterprise Linux (RHEL), is ideal for deploying Dnsmasq as a DHCP server. By enabling Dnsmasq’s integrated DHCP feature, you can streamline network configurations, efficiently allocate IP addresses, and manage DNS queries simultaneously.

This article will provide a step-by-step guide on enabling the integrated DHCP feature in Dnsmasq and configuring it as a DHCP server on AlmaLinux.

Table of Contents

1. Prerequisites
2. Installing Dnsmasq on AlmaLinux
3. Configuring Dnsmasq for DHCP
4. Understanding the Configuration File
5. Starting and Enabling the Dnsmasq Service
6. Testing the DHCP Server
7. Troubleshooting Common Issues
8. Conclusion

1. Prerequisites

Before starting, ensure you meet the following prerequisites:

• AlmaLinux Installed: A running instance of AlmaLinux with root or sudo access.
• Network Information: Have details of your network, including the IP range, gateway, and DNS servers.
• Firewall Access: Ensure the firewall allows DHCP traffic (UDP ports 67 and 68).

2. Installing Dnsmasq on AlmaLinux

Dnsmasq is available in AlmaLinux’s default package repositories. Follow these steps to install it:

1. Update System Packages: Open a terminal and update the system packages to ensure all dependencies are up to date:

   sudo dnf update -y
   

2. Install Dnsmasq: Install the Dnsmasq package using the following command:

   sudo dnf install dnsmasq -y
   

3. Verify Installation: Check if Dnsmasq is installed correctly:

   dnsmasq --version
   

   You should see the version details of Dnsmasq.

3. Configuring Dnsmasq for DHCP

Once Dnsmasq is installed, you need to configure it to enable the DHCP feature. Dnsmasq uses a single configuration file located at /etc/dnsmasq.conf.

1. Backup the Configuration File: It’s a good practice to back up the original configuration file before making changes:

   sudo cp /etc/dnsmasq.conf /etc/dnsmasq.conf.backup
   

2. Edit the Configuration File: Open the configuration file in your preferred text editor:

   sudo nano /etc/dnsmasq.conf
   

   Uncomment and modify the following lines to enable the DHCP server:

   • Define the DHCP Range: Specify the range of IP addresses to allocate to clients:

     dhcp-range=192.168.1.100,192.168.1.200,12h
     

     Here:

     • 192.168.1.100 and 192.168.1.200 define the start and end of the IP range.
     • 12h specifies the lease time (12 hours in this example).

   • Set the Default Gateway (Optional): If your network has a specific gateway, define it:

     dhcp-option=3,192.168.1.1
     

   • Specify DNS Servers (Optional): Define DNS servers for clients:

     dhcp-option=6,8.8.8.8,8.8.4.4
     

3. Save and Exit: Save the changes and exit the editor. For nano, press Ctrl+O to save, then Ctrl+X to exit.

4. Understanding the Configuration File

Key Sections of /etc/dnsmasq.conf

• dhcp-range: Defines the range of IP addresses and the lease duration.

• dhcp-option: Configures network options such as gateways and DNS servers.

• log-queries (Optional): Enables logging for DNS and DHCP queries for debugging purposes:

  log-queries
  log-dhcp
  

Dnsmasq’s configuration is straightforward, making it an excellent choice for small networks.

5. Starting and Enabling the Dnsmasq Service

Once the configuration is complete, follow these steps to start and enable Dnsmasq:

1. Start the Service:

   sudo systemctl start dnsmasq
   

2. Enable the Service at Boot:

   sudo systemctl enable dnsmasq
   

3. Verify Service Status: Check the status to ensure Dnsmasq is running:

   sudo systemctl status dnsmasq
   

   The output should indicate that the service is active and running.

6. Testing the DHCP Server

To confirm that the DHCP server is functioning correctly:

1. Restart a Client Machine: Restart a device on the same network and set it to obtain an IP address automatically.

2. Check Allocated IP: Verify that the client received an IP address within the defined range.

3. Monitor Logs: Use the following command to monitor DHCP allocation in real-time:

   sudo tail -f /var/log/messages
   

   Look for entries indicating DHCPDISCOVER and DHCPOFFER transactions.

7. Troubleshooting Common Issues

Issue 1: Dnsmasq Fails to Start

• Solution: Check the configuration file for syntax errors:

  sudo dnsmasq --test
  

Issue 2: No IP Address Assigned

• Solution:

  • Verify that the firewall allows DHCP traffic:

    sudo firewall-cmd --add-service=dhcp --permanent
    sudo firewall-cmd --reload
    

  • Ensure no other DHCP server is running on the network.

Issue 3: Conflicting IP Address

• Solution: Ensure the IP range specified in dhcp-range does not overlap with statically assigned IP addresses.

8. Conclusion

By following this guide, you’ve successfully enabled the integrated DHCP feature in Dnsmasq and configured it as a DHCP server on AlmaLinux. Dnsmasq’s lightweight design and simplicity make it an ideal choice for small to medium-sized networks, offering robust DNS and DHCP capabilities in a single package.

Regularly monitor logs and update configurations as your network evolves to ensure optimal performance. With Dnsmasq properly configured, you can efficiently manage IP address allocation and DNS queries, streamlining your network administration tasks.

For more advanced configurations, such as PXE boot or VLAN support, refer to the official Dnsmasq documentation.