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At the end i am giving screen shot of DORA captured message by Wireshark Monitoriing tool.
Client-server interaction - allocating a network address
The following summary of the protocol exchanges between clients and
servers refers to the DHCP messages described in table 2. The
timeline diagram in figure 3 shows the timing relationships in a
typical client-server interaction. If the client already knows its
address, some steps may be omitted; this abbreviated interaction is
described in section 3.2.
1. The client broadcasts a DHCPDISCOVER message on its local physical
subnet. The DHCPDISCOVER message may include options that suggest
values for the network address and lease duration. BOOTP relay
agents may pass the message on to DHCP servers not on the same
physical subnet.
2. Each server may respond with a DHCPOFFER message that includes an
available network address in the 'yiaddr' field (and other
configuration parameters in DHCP options). Servers need not
reserve the offered network address, although the protocol will
work more efficiently if the server avoids allocating the offered
network address to another client. The server unicasts the
DHCPOFFER message to the client (using the DHCP/BOOTP relay agent
if necessary) if possible, or may broadcast the message to a
broadcast address (preferably 255.255.255.255) on the client's
subnet.
3. The client receives one or more DHCPOFFER messages from one or
more servers. The client may choose to wait for multiple
responses. The client chooses one server from which to request
configuration parameters, based on the configuration parameters
offered in the DHCPOFFER messages. The client broadcasts a
DHCPREQUEST message that MUST include the 'server identifier'
option to indicate which server it has selected, and may include
other options specifying desired configuration values. This
DHCPREQUEST message is broadcast and relayed through DHCP/BOOTP
relay agents. To help ensure that any DHCP/BOOTP relay agents
forward the DHCPREQUEST message to the same set of DHCP servers
that received the original DHCPDISCOVER message, the DHCPREQUEST
message must use the same value in the DHCP message header's
'secs' field and be sent to the same IP broadcast address as the
original DHCPDISCOVER message. The client times out and
retransmits the DHCPDISCOVER message if the client receives no
DHCPOFFER messages.
4. The servers receive the DHCPREQUEST broadcast from the client.
Those servers not selected by the DHCPREQUEST message use the
message as notification that the client has declined that server's
offer. The server selected in the DHCPREQUEST message commits the
binding for the client to persistent storage and responds with a
DHCPACK message containing the configuration parameters for the
requesting client. The combination of 'chaddr' and assigned
network address constitute an unique identifier for the client's
lease and are used by both the client and server to identify a
lease referred to in any DHCP messages. The 'yiaddr' field in the
DHCPACK messages is filled in with the selected network address.
If the selected server is unable to satisfy the DHCPREQUEST message
(e.g., the requested network address has been allocated), the
server SHOULD respond with a DHCPNAK message.
