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\section { DHCP Process}
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\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.
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\item \textbf { DHCPINFORM:} A client already has an \acrshort { ip} address but is requesting other configuration parameters that the \acrshort { dhcp} server is configured to deliver such as \acrshort { dns} address.
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\end { itemize}
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\section { DHCP Options}
\begin { itemize}
\item \textbf { 43} Vendor-encapsulated option that enables vendors to have their own list of options on the server.
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\item \textbf { 69} \acrshort { smtp} server, if you want to specify available \acrshort { smtp} servers to the client.
\item \textbf { 70} \acrshort { pop3} server, if you want to specify available \acrshort { pop3} servers to the client.
\item \textbf { 150} \acrshort { tftp} server that enables your phones to access a list of \acrshort { tftp} servers.
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\end { itemize}
\section { DHCP Example Configuration}
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\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}
