Dell PowerEdge FX2/FX2s - Manual (Page 60)

DHCPDECLINE A client sends this message to the server in response to a DHCPACK if the
configuration parameters are unacceptable; for example, if the offered address is
already in use. In this case, the client starts the configuration process over by
sending a DHCPDISCOVER.
DHCPINFORM A client uses this message to request configuration parameters when it assigned an
IP address manually rather than with DHCP. The server responds by unicast.
DHCPNAK A server sends this message to the client if it is not able to fulfill a DHCPREQUEST;
for example, if the requested address is already in use. In this case, the client starts
the configuration process over by sending a DHCPDISCOVER.
DHCPRELEASE A DHCP client sends this message when it is stopped forcefully to return its IP
address to the server.
Figure 5. Assigning Network Parameters using DHCP
60 Dynamic Host Configuration Protocol (DHCP)