EVB-B1+ WIZnet, EVB-B1+ Datasheet - Page 77

• Manufacturer Part Number: EVB-B1+
• Description: Development Boards & Kits - ARM W3150A+EVAL BOARD BASED ON AVR
• Manufacturer: WIZnet

Specifications of EVB-B1+

• Rohs: yes
• Product: Evaluation Boards
• Interface Type: RS-232, SPI
• Operating Supply Voltage: 3.3 V, 5 V
• Data Bus Width: 8 bit
• Dimensions: 50 mm x 40 mm
• Processor Series: ATmega128

3.2.6.5.
DHCP Client
DHCP Client program is a program that assigns the network information from DHCP server in the network.
Note that DHCP Client program must be started prior to other programs because it manages Network
Information setup. First, review basic facts on DHCP(Dynamic Host Configuration Protocol) and get further
into the usage of DHCP Client program.
DHCP uses UDP protocol in Transport Layer and communicates with DHCP server using broadcast of UDP.
The reason why it uses broadcast is because it has no IP address and the IP address of server is unknown.
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When UDP broadcast at W3150A
, destination IP address needs to be set ’255.255.255.255’ for broadcast
packet transmission.
<Fig 3.25> is a Message Flow between DHCP Server and Client.
<Fig 3.25: DHCP Message Flow>
First of all, DHCP client broadcasts DISCOVERY message to the local Network. If DHCP server exists at the
network then DHCP server receives Discovery message and provides network Information such as IP, G/W
IP, Subnet Mask, and DNS sever IP which can be used by DHCP Client, and information such as Lease
Time to the DHCP Client as OFFER message. DHCP Client can detect DHCP server by receiving the
OFFER message and then it sends REQUEST message to DHCP server to use the information suggested
by DHCP server. After receiving REQUEST message from DHCP Client, DHCP server finds out if the
requested network information is usable. If it is, it sends ACK message, if not, NACK message is sent to
DHCP Client. After receiving ACK message from DHCP server, DHCP Client uses the offered network
information. The network information is valid only for the Lease Time suggested by DHCP server. Hence, if
DHCP Client wants to keep using the network information, it retransmits REQUEST message to DHCP
server to maintain network information usually after half of the Lease Time. In this process, DHCP client can
get same or new network information from DHCP server. In case that it receives new network information,
the new one must be used.
Message between DHCP server and client has the format as in <Fig 3.26> with the size of 544 Bytes. Refer
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