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DHCP Server (Only on Ubuntu 20.04 and above versions)

This guide provides step-by-step instructions to set up a DHCP server using dnsmasq on a specific network interface.

Prerequisites

Before you begin, ensure you have the following:

  • A Linux machine with a network interface for serving DHCP.
  • dnsmasq installed.
  • Sudo privileges on the machine.

Step 1: Install Dnsmasq

To install dnsmasq, use your distribution's package manager. On a Debian/Ubuntu-based system, you can run:

sudo apt update
sudo apt install dnsmasq

Step 2: List interface

To list avaialbe interface in the linux machine, you can run:

ip a

This will give the network interface name

Step 3: Configure dnsmasq

Edit the dnsmasq configuration file, usually located at /etc/dnsmasq.conf (which is the default configuration). But the best advised method is to create a new configuration file under /etc/dnsmasq.d. Here's a basic configuration for dnsmasq as a DHCP server:

# /etc/dnsmasq.d/eth0-dnscpser.conf

# Enable DHCP server on a specific interface
interface=eth0   # Replace with your network interface

# Specify the range of IP addresses to allocate for DHCP clients
dhcp-range=192.168.1.100,192.168.1.150,12h   # Start, end of range, lease time

# Define the default gateway for DHCP clients
dhcp-option=option:router,192.168.1.1

# Define DNS server for clients
dhcp-option=option:dns-server,8.8.8.8,8.8.4.4

# Define subnet mask for the network
dhcp-option=option:netmask,255.255.255.0

# Optional: Define a static IP mapping for specific clients
dhcp-host=00:11:22:33:44:55,192.168.1.50   # MAC address and static IP

Step 4: Start and Enable dnsmasq

Once the configuration is ready, restart the dnsmasq service and enable it to start on boot:

sudo systemctl restart dnsmasq
sudo systemctl enable dnsmasq

Step 5: Verify the DHCP Lease

To verify that dnsmasq is working correctly, you can check the DHCP leases file, usually located at /var/lib/misc/dnsmasq.leases. This file contains information about the current DHCP leases.

cat /var/lib/misc/dnsmasq.leases

Step 6: Troubleshooting

If things aren’t working as expected, check the system logs for dnsmasq messages to see if there are any errors: 

sudo journalctl -xe | grep dnsmasq

This setup provides a basic dnsmasq-based DHCP server that serves IP addresses in the range 192.168.1.100 to 192.168.1.150 for 12 hours. You can adjust this based on your requirements.

Note

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