DHCP

networkingIT support

Dynamic Host Configuration Protocol: hands each joining device an IP address, mask, gateway, and DNS servers, leased for a limited time.

The four-step dance is DORA: Discover, Offer, Request, Acknowledge.

DHCP hands a client its address, gateway, DNS servers and often much more, through a four-message exchange that ends in a lease with a finite lifetime. Renewal happens at half the lease time, which is why a client can survive a server restart without noticing.

The operational subtleties are in the options and the relay. Everything from boot filenames to time servers to vendor-specific configuration rides in DHCP options, which is why a device that boots incorrectly is often reading an option nobody remembers setting. Across subnets a relay agent forwards requests to a central server, and the classic fault is a client that gets no address because the relay was configured on the router but not on the specific interface.

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