Dhcp Server Configuration; Introduction To Dhcp Server; Usage Of Dhcp Server; Dhcp Fundamentals - 3Com 5500-SI Configuration Manual

10
Introduction to DHCP
Server

Usage of DHCP Server

DHCP Fundamentals

DHCP S
ERVER
This section contains configuration introduction on DHCP Server.
Generally, DHCP servers are used in the following networks to assign IP addresses:
Large-sized networks, where manual configuration method bears heavy load and
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is difficult to manage the whole network in centralized way.
Networks where the number of available IP addresses is less than that of the hosts.
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In this type of networks, IP addresses are not enough for all the hosts to obtain a
fixed IP address, and the number of on-line users is limited (such is the case in an
ISP network). In these networks, a great number of hosts must dynamically obtain
IP addresses through DHCP.
Networks where only a few hosts need fixed IP addresses and most hosts do not
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need fixed IP addresses.
Obtain IP address dynamically
A DHCP client undergoes the following four phases to dynamically obtain an IP
address from a DHCP server.
Discover: The DHCP client tries to find a DHCP server by broadcasting a
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DHCP-DISCOVER packet.
Offer: Each DHCP server that receives the DHCP-DISCOVER packet chooses an
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unassigned IP address from the address pool and sends a DHCP-OFFER packet
(which carries the IP address and other configuration information) to the DHCP
client.
Select: If more than one DHCP server sends a DHCP-OFFER packet to the DHCP
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client, the DHCP client only accepts the DHCP-OFFER packet that first arrives, and
then broadcasts a DHCP-REQUEST packet containing the assigned IP address
carried in the DHCP-OFFER packet.
Acknowledge: Upon receiving the DHCP-REQUEST packet, the DHCP server
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returns a DHCP-ACK packet to the DHCP client to confirm the assignment of the
IP address to the client, or returns a DHCP-NAK packet to refuse the assignment of
the IP address to the client. When the client receives the DHCP-ACK packet, it
broadcasts an ARP packet with the assigned IP address as the destination address
to detect the assigned IP address, and uses the IP address only if it does not receive
any response within a specified period.
The IP addresses offered by other DHCP servers (if any) are not used by the DHCP
client and are still available to other clients.
C
ONFIGURATION