Supplying DHCP options is a smart way to configure network clients during the early phase of network access deployment. In addition to providing the IP address, the DHCP protocol is able to set a large bunch of options that are very useful for device configuration.
DHCP is an evolution of the BOOTP protocol (see RFC951) designed at first to bootstrap a diskless client. When starting such a device, BOOTP provides sufficient configuration parameters for obtaining network access, firmware and software locations for images to be downloaded from a network file repository.
X11 diskless display screen no longer exists, but many devices can take advantage of being configured at their network access time – for example IoT devices. BOOTP, which brings additional option configuration to the historical RARP protocol (see RFC903) which provides only IP address, has itself evolved in the DHCP protocol. With pool management and device mobility DHCP is also able to handle a wide list of options to configure a lot of various devices.
Each option has a name and a numerical identifier to be transported in the protocol frames. DHCP server configuration can handle providing options to all devices asking for an IP address and also bound to a specific client identifier or mac address family.
Any client entering the network can ask for specific DHCP options in addition to its IP address (eg vendor class, hostname or authentication credentials). The list of options requested is generally used to fingerprint the DHCP clients on the network. Finally, DHCP options can be inserted by a relay agent that is forwarding a broadcasted request from the local network to a central DHCP server.
references:
https://www.efficientip.com/glossary/dhcp-option/
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