\subsubsection{Using the network scripts} To be able to access the network functions, you need to include the necessary shell scripts by running: \begin{Verbatim} . /etc/functions.sh # common functions include /lib/network # include /lib/network/*.sh scan_interfaces # read and parse the network config \end{Verbatim} Some protocols, such as PPP might change the configured interface names at run time (e.g. \texttt{eth0} => \texttt{ppp0} for PPPoE). That's why you have to run \texttt{scan\_interfaces} instead of reading the values from the config directly. After running \texttt{scan\_interfaces}, the \texttt{'ifname'} option will always contain the effective interface name (which is used for IP traffic) and if the physical device name differs from it, it will be stored in the \texttt{'device'} option. That means that running \texttt{config\_get lan ifname} after \texttt{scan\_interfaces} might not return the same result as running it before. After running \texttt{scan\_interfaces}, the following functions are available: \begin{itemize} \item{\texttt{find\_config \textit{interface}}} \\ looks for a network configuration that includes the specified network interface. \item{\texttt{setup\_interface \textit{interface [config] [protocol]}}} \\ will set up the specified interface, optionally overriding the network configuration name or the protocol that it uses. \end{itemize} \subsubsection{Writing protocol handlers} You can add custom protocol handlers by adding shell scripts to \texttt{/lib/network}. They provide the following two shell functions: \begin{Verbatim} scan_<protocolname>() { local config="$1" # change the interface names if necessary } setup_interface_<protocolname>() { local interface="\$1" local config="\$2" # set up the interface } \end{Verbatim} \texttt{scan\_\textit{protocolname}} is optional and only necessary if your protocol uses a custom device, e.g. a tunnel or a PPP device.