If a client has obtained a network address through some other means (e.g., manual configuration), it may use a DHCPINFORM request message to obtain other local configuration parameters. Servers receiving a DHCPINFORM message construct a DHCPACK message with any local configuration parameters appropriate for the client without: allocating a new address, checking for an existing binding, filling in 'yiaddr' or including lease time parameters. The servers SHOULD unicast the DHCPACK reply to the address given in the 'ciaddr' field of the DHCPINFORM message.
The server SHOULD check the network address in a DHCPINFORM message for consistency, but MUST NOT check for an existing lease. The server forms a DHCPACK message containing the configuration parameters for the requesting client and sends the DHCPACK message directly to the client.