RFC 2131 Citat: "...The server MUST broadcast the DHCPNAK message to the 0xffffffff broadcast address because the client may not have a correct network address or subnet mask, and the client may not be answering ARP requests...Normally, DHCP servers and BOOTP relay agents attempt to deliver DHCPOFFER, DHCPACK and DHCPNAK messages directly to the client using u[n]icast delivery...If the BROADCAST bit is cleared to 0, the message SHOULD be sent as an IP unicast to the IP address specified in the 'yiaddr' field..."
