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Chapter 9 DHCP
DHCP (Dynamic Host Configuration Protocol) is a client-server protocol which is widely used in
LAN environments to dynamically assign host IP addresses from a centralized server.
As workstations and personal computers proliferate on the Internet, the administrative complexity
of maintaining a network is increased by an order of magnitude. The assignment of local network
resources to each client represents one such difficulty. In most environments, delegating such
responsibility to the user is not plausible and, indeed, the solution is to define the resources in
uniform terms, and to automate their assignment.
The DHCP dealt with the issue of assigning an internet address to a client, as well as some other
resources.
DHCP Elements
DHCP is built on a client-server model, where designated DHCP server hosts allocate network
addresses and deliver configuration parameters to DHCP clients. Generally a DHCP server can
allocate configuration parameters to more than one client. Figure 9-1 shows you the model.
Figure 9-1 DHCP model
To meet the different requirements of DHCP clients, DHCP server is always designed to supply
hosts with the configuration parameters in three policies.
1) Manual Assignment: For the specific DHCP clients (e.g., web server), the configuration
parameters are manually specified by the administrator and are assigned to these clients via
a DHCP server.
2) Automatic Assignment: The DHCP server must supplies the configuration parameters to
DHCP client with the lease time continued forever.
3) Dynamic Assignment: A network administrator assigns a range of IP addresses to DHCP
server, and each client computer on the LAN is configured to request an IP address from the
DHCP server with a fixed period of time (e.g., 2 hours), allowing the DHCP server to reclaim
(and then reallocate) IP addresses that are not renewed.
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