Step 1: Install dnsmasq

1. Update your package list:

   sudo apt update

2. Install dnsmasq:

   sudo apt install dnsmasq

Step 2: Configure dnsmasq

1. Backup the default configuration file:

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

2. Edit the dnsmasq configuration file:

   sudo nano /etc/dnsmasq.conf

3. Add the following configuration to set up DHCP and DNS:

   # Listen on a specific interface (e.g., eth0 or enp0s3)
   interface=enp0s3
    
   # Enable DHCP
   dhcp-range=192.168.1.100,192.168.1.200,12h
    
   # Set the gateway (router) IP
   dhcp-option=3,192.168.1.1
    
   # Set the DNS server (e.g., Google DNS)
   dhcp-option=6,8.8.8.8,8.8.4.4
    
   # Enable DNS service
   no-resolv
   server=8.8.8.8
   server=8.8.4.4

   Replace enp0s3 with your network interface name (use ip a to check). Adjust the IP ranges and gateway as needed.

4. Save and exit the file (Ctrl+O, Enter, Ctrl+X).

Step 3: Restart dnsmasq

1. Restart the dnsmasq service to apply the changes:

   sudo systemctl restart dnsmasq

2. Enable dnsmasq to start on boot:

   sudo systemctl enable dnsmasq

Step 4: Verify the Setup

1. Check the status of dnsmasq:

   sudo systemctl status dnsmasq

2. Test DHCP by connecting a client device to the network. It should automatically receive an IP address in the range you specified.

3. Test DNS by pinging a domain name from a client:

   ping google.com

Step 5: (Optional) Configure Firewall

If you have a firewall enabled (e.g., ufw), allow DHCP and DNS traffic:

sudo ufw allow 53/tcp  # DNS
sudo ufw allow 53/udp  # DNS
sudo ufw allow 67/udp  # DHCP
sudo ufw allow 68/udp  # DHCP

Step 6: Troubleshooting

1. Check logs for errors:

   sudo journalctl -u dnsmasq

2. If clients are not receiving IP addresses, ensure:

   • The correct network interface is configured.
   • No other DHCP server is running on the network.

Resolving Port 53 Conflicts

Your system doesn’t have net-tools installed, which includes netstat. You can install it with:

sudo apt update && sudo apt install net-tools -y

After that, run:

sudo netstat -tulnp | grep ":53 "

If you prefer an alternative without installing net-tools, use:

sudo ss -tulnp | grep ":53 "

This will check which process is using port 53, which is crucial for resolving the dnsmasq issue.

If systemd-resolved is using port 53, you can:

1. Disable systemd-resolved:

   sudo systemctl stop systemd-resolved
   sudo systemctl disable systemd-resolved

2. Remove the symlink:

   sudo rm /etc/resolv.conf

3. Create a new resolv.conf file:

   sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

4. Restart dnsmasq:

   sudo systemctl restart dnsmasq

This should free up port 53 for dnsmasq and allow it to run properly.