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\title{Basic Configuration of dnsmasq in an Incus Container on Debian with Netplan}
\author{}
\date{}
\maketitle

\section{Introduction}
This guide provides step-by-step instructions for setting up \texttt{dnsmasq} as a DNS and DHCP server in an Incus container running Debian. The network configuration is managed using Netplan to ensure proper network integration.

\section{Prerequisites}
Before proceeding, ensure the following:
\begin{itemize}
  \item Incus is installed on the host system (\texttt{sudo apt install incus}).
  \item A Debian-based container is created in Incus.
  \item Basic knowledge of Linux networking and container management.
  \item Root or sudo access to the host and container.
\end{itemize}

\section{Step-by-Step Configuration}

\subsection{Creating and Setting Up the Incus Container}
% Creating the Incus container
Create a Debian container named \texttt{dnsmasq-container} using the following command on the host:
\begin{lstlisting}[language=bash]
incus create images:debian/12 dnsmasq-container
incus config set dnsmasq-container security.syscalls.intercept.mount true
incus start dnsmasq-container
\end{lstlisting}
The \texttt{security.syscalls.intercept.mount} setting is required for \texttt{dnsmasq} to function correctly in the container.

% Accessing the container
Access the container:
\begin{lstlisting}[language=bash]
incus exec dnsmasq-container -- bash
\end{lstlisting}

\subsection{Installing dnsmasq}
% Installing dnsmasq and dependencies
Update the package list and install \texttt{dnsmasq}:
\begin{lstlisting}[language=bash]
apt update
apt install dnsmasq -y
\end{lstlisting}

\subsection{Configuring the Network with Netplan}
% Setting up the network interface
Configure the container's network using Netplan to assign a static IP address. Edit the Netplan configuration file (e.g., \texttt{/etc/netplan/01-netcfg.yaml}):
\begin{lstlisting}[language=bash]
nano /etc/netplan/01-netcfg.yaml
\end{lstlisting}
Add the following configuration:
\begin{lstlisting}[language=yaml]
network:
  version: 2
  ethernets:
    eth0:
      dhcp4: no
      addresses:
        - 192.168.1.10/24
      gateway4: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
\end{lstlisting}
Apply the configuration:
\begin{lstlisting}[language=bash]
netplan apply
\end{lstlisting}

\subsection{Configuring dnsmasq}
% Configuring dnsmasq for DNS and DHCP
Edit the \texttt{dnsmasq} configuration file at \texttt{/etc/dnsmasq.conf}:
\begin{lstlisting}[language=bash]
nano /etc/dnsmasq.conf
\end{lstlisting}
Add or modify the following settings to enable DNS and DHCP:
\begin{lstlisting}
# DNS settings
domain-needed
bogus-priv
no-resolv
server=8.8.8.8
server=8.8.4.4
local=/example.local/
domain=example.local

# DHCP settings
dhcp-range=192.168.1.100,192.168.1.200,12h
dhcp-option=3,192.168.1.1
dhcp-option=6,8.8.8.8,8.8.4.4
\end{lstlisting}

\textbf{Explanation:}
\begin{itemize}
  \item \texttt{domain-needed}: Prevents incomplete domain names from being sent to upstream DNS.
  \item \texttt{bogus-priv}: Blocks reverse DNS lookups for private IP ranges.
  \item \texttt{no-resolv}: Disables reading \texttt{/etc/resolv.conf}.
  \item \texttt{server}: Specifies upstream DNS servers (Google DNS in this case).
  \item \texttt{local} and \texttt{domain}: Configures a local domain.
  \item \texttt{dhcp-range}: Defines the IP range for DHCP clients (from 192.168.1.100 to 192.168.1.200, lease time 12 hours).
  \item \texttt{dhcp-option}: Sets the default gateway (option 3) and DNS servers (option 6).
\end{itemize}

\subsection{Starting and Enabling dnsmasq}
% Starting the dnsmasq service
Restart the \texttt{dnsmasq} service to apply the configuration:
\begin{lstlisting}[language=bash]
systemctl restart dnsmasq
systemctl enable dnsmasq
\end{lstlisting}
Verify that \texttt{dnsmasq} is running:
\begin{lstlisting}[language=bash]
systemctl status dnsmasq
\end{lstlisting}

\subsection{Testing the Configuration}
% Testing DNS and DHCP
Test the DNS resolution from within the container:
\begin{lstlisting}[language=bash]
nslookup example.local 192.168.1.10
\end{lstlisting}
To test DHCP, connect a client device to the same network and verify that it receives an IP address in the range \texttt{192.168.1.100--192.168.1.200}.

\section{Troubleshooting}
If \texttt{dnsmasq} fails to start:
\begin{itemize}
  \item Check the logs: \texttt{journalctl -u dnsmasq}.
  \item Ensure no other service is using port 53 (DNS) or 67 (DHCP).
  \item Verify the network configuration with \texttt{ip a} and \texttt{ping 8.8.8.8}.
\end{itemize}

\section{Conclusion}
This guide configures \texttt{dnsmasq} as a DNS and DHCP server in an Incus container on Debian. The Netplan configuration ensures proper network setup. For advanced configurations, refer to the \texttt{dnsmasq} documentation (\texttt{man dnsmasq}).

\end{document}