How DHCP Works

DHCP eliminates the need for you to manually configure your system’s TCP/IP information, and instead fetches that information from a central server. A program called dhclient allows FreeBSD to act as a DHCP client. When a system configured to use DHCP boots and dhclient starts, it sends out broadcast requests on UDP port 68, looking for any server on the LAN that will respond with DHCP information. Because these datagrams are sent to the broadcast address (255.255.255.255), it doesn’t matter that the client machine doesn’t have any TCP/IP information configured yet.

If there is a DHCP server on the network, it listens on port 68 for these requests. When it receives a request for configuration information, it checks its database ...

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