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MAGNUM 6K SWITCHES, MNS-6K USER GUIDE
The client broadcasts on the physical subnet to find available servers. Network administrators can
configure a local router to forward DHCP packets to a DHCP server on a different subnet. This
client-implementation creates a UDP packet with the broadcast destination of 255.255.255.255 or
subnet broadcast address.
A client can also request its last-known IP address. If the client is still in a network where this IP
is valid, the server might grant the request. Otherwise, it depends whether the server is set up as
authoritative or not. An authoritative server will deny the request, making the client ask for a new
IP immediately. A non-authoritative server simply ignores the request, leading to an
implementation dependent time out for the client to give up on the request and ask for a new IP.
DHCP Offers
When a DHCP server receives an IP lease request from a client, it extends an IP lease offer. This
is done by reserving an IP address for the client and sending a DHCPOFFER message across the
network to the client. This message contains the client's MAC address, followed by the IP address
that the server is offering, the subnet mask, the lease duration, and the IP address of the DHCP
server making the offer. The server determines the configuration, based on the client's hardware
address as specified in the CHADDR field. The server specifies the IP address in the YIADDR
field.
DHCP Request
When the client PC receives an IP lease offer, it must tell all the other DHCP servers that it has
accepted an offer. To do this, the client broadcasts a DHCPREQUEST message containing the
IP 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 address
that they had reserved for the client back to the pool of valid addresses that they can offer to
another computer. Any number of DHCP servers can respond to an IP lease request, but the
client can only accept one offer per network interface card.
DHCP Acknowledgement
When the DHCP server receives the DHCPREQUEST message from the client, it initiates the
final phase of the configuration process. This acknowledgement phase involves sending a
DHCPACK packet to the client. This packet includes the lease duration and any other
configuration information that the client might have requested. At this point, the TCP/IP
configuration process is complete. The server acknowledges the request and sends the
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