DHCPClients

DHCP clients are software or firmware components that obtain network configuration from a Dynamic Host Configuration Protocol (DHCP) server. They are present in most operating systems, smartphones, printers, and many network devices such as routers and access points. The client automates IP address assignment and other settings, reducing the need for manual configuration.

Operation follows a four-step handshake. When a device joins a network, the DHCP client broadcasts a DHCPDISCOVER message to locate a DHCP server. A server may respond with a DHCPOFFER that includes an available IP address and configuration options. The client selects an offer and sends a DHCPREQUEST to indicate its intent to use that address. The server then replies with a DHCPACK to finalize the lease. If the offered address is no longer suitable, the server may issue a DHCPNAK, prompting the client to restart the process.

A DHCP lease is time-limited. Each lease has a duration, after which the client must renew. Renewal typically occurs when the client reaches the T1 time; if renewal fails, the client will attempt to rebind at T2 or obtain a new address upon lease expiration. The client can also release its address explicitly.

Servers supply configuration options such as IP address, subnet mask, default gateway, DNS servers, domain search list, NTP servers, and other vendor-specific options. They can also provide PXE-related information for network boot, such as boot file name and server address.

DHCP is defined for IPv4 (DHCP) and IPv6 is served by DHCPv6. DHCPv6 uses a different message exchange (Solicit, Advertise, Request, Reply) and can operate with or alongside Router Advertisements. In practice, many devices implement both IPv4 and IPv6 DHCP clients.

Security and management: DHCP lacks built-in authentication, relying on trusted networks. Unauthenticated servers or rogue devices can misconfigure clients. Defensive measures include DHCP snooping, network segmentation, ACLs, and monitoring for unusual lease activity.