\chapter{DHCP}

\section{DHCP Process}

\fig{dhcp/dhcpdiscoverprocess}{dhcpdiscoverprocess}{DHCP Discover Process}

\subsection{DHCP Messages}

\begin{itemize}
    \item \textbf{DHCPDECLINE:} Message sent from the client to the server that the address is already in use.
    \item \textbf{DHCPNAK:} The server sends a refusal to the client for request for configuration.
    \item \textbf{DHCPRELEASE:} Client tells a server that it is giving up a lease.
    \item \textbf{DHCPINFORM:} A client already has an \gls{ip} address but is requesting other configuration parameters that the \gls{dhcp} server is configured to deliver such as \gls{dns} address.
\end{itemize}

\section{DHCP Options}

\begin{itemize}
    \item \textbf{43} Vendor-encapsulated option that enables vendors to have their own list of options on the server.
    \item \textbf{69} \gls{smtp} server, if you want to specify available \gls{smtp} servers to the client.
    \item \textbf{70} \gls{pop3} server, if you want to specify available \gls{pop3} servers to the client.
    \item \textbf{150} \gls{tftp} server that enables your phones to access a list of \gls{tftp} servers.
\end{itemize}

\section{DHCP Example Configuration}

\subsection{Cisco}

\begin{txt}
    ip dhcp excluded-address 192.168.0.254
    !
    ip dhcp pool LAN-1-POOL-DHCP
    network 192.168.0.0 255.255.255.0
    default-router 192.168.0.254
    lease 2 ! set in days
\end{txt}

When configuring a Layer 3 interface as a relay port for DHCP request for a subnet. Set the ip helper command on the interface with one \textit{or} more ip addresses.

\begin{txt}
    interface GigabitEthernet 0/3
    ip helper-address 192.168.220.220
    ip helper-address 192.168.222.222
\end{txt}