M A G N U M 6 K S W I T C H E S , M N S - 6 K U S E R G U I D EThe client broadcasts on the physical subnet to find available servers. Network administrators canconfigure a local router to forward DHCP packets to a DHCP server on a different subnet. Thisclient-implementation creates a UDP packet with the broadcast destination of 255.255.255.255 orsubnet broadcast address.A client can also request its last-known IP address. If the client is still in a network where this IPis valid, the server might grant the request. Otherwise, it depends whether the server is set up asauthoritative or not. An authoritative server will deny the request, making the client ask for a newIP immediately. A non-authoritative server simply ignores the request, leading to animplementation dependent time out for the client to give up on the request and ask for a new IP.DHCP OffersWhen a DHCP server receives an IP lease request from a client, it extends an IP lease offer. Thisis done by reserving an IP address for the client and sending a DHCPOFFER message across thenetwork to the client. This message contains the client's MAC address, followed by the IP addressthat the server is offering, the subnet mask, the lease duration, and the IP address of the DHCPserver making the offer. The server determines the configuration, based on the client's hardwareaddress as specified in the CHADDR field. The server specifies the IP address in the YIADDRfield.DHCP RequestWhen the client PC receives an IP lease offer, it must tell all the other DHCP servers that it hasaccepted an offer. To do this, the client broadcasts a DHCPREQUEST message containing theIP address of the server that made the offer. When the other DHCP servers receive this message,they withdraw any offers that they might have made to the client. They then return the addressthat they had reserved for the client back to the pool of valid addresses that they can offer toanother computer. Any number of DHCP servers can respond to an IP lease request, but theclient can only accept one offer per network interface card.DHCP AcknowledgementWhen the DHCP server receives the DHCPREQUEST message from the client, it initiates thefinal phase of the configuration process. This acknowledgement phase involves sending aDHCPACK packet to the client. This packet includes the lease duration and any otherconfiguration information that the client might have requested. At this point, the TCP/IPconfiguration process is complete. The server acknowledges the request and sends the80
