H3C Technologies H3C SecPath F1000-E - Manual (Page 232)

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DHCP Server Configuration
Introduction to DHCP Server
Application Environment
The DHCP server is well suited to the network where:
• It is hard to implement manual configuration and centralized management.
• The hosts are more than the assignable IP addresses and it is impossible to assign a fixed IP
address to each host. For example, an ISP limits the number of hosts accessing the Internet at a
time, so lots of hosts need to acquire IP addresses dynamically.
• A few hosts need fixed IP addresses.
DHCP Address Pool
Address pool structure
In response to a client’s request, the DHCP server selects an idle IP address from an address pool and
sends it together with other parameters such as lease and DNS server address to the client.
The address pool database is organized as a tree. The root of the tree is the address pool for natural
networks, branches are address pools for subnets, and leaves are addresses statically bound to clients.
For the same level address pools, a previously configured pool has a higher selection priority than a
new one.
At the very beginning, subnetworks inherit network parameters and clients inherit subnetwork
parameters. Therefore, common parameters, for example a DNS server address, should be configured
at the highest (network or subnetwork) level of the tree.
After establishment of the inheritance relationship, the new configuration at the higher level (father) of
the tree will be:
• Inherited if the lower level (child) has no such configuration, or
• Overridden if the lower level (child) has such configuration.
NOTE:
The IP address lease does not enjoy the inheritance attribute.
Principles for selecting an address pool
The DHCP server observes the following principles to select an address pool when assigning an IP
address to a client:
1. If there is an address pool where an IP address is statically bound to the MAC address or ID of the
client, the DHCP server will select this address pool and assign the statically bound IP address to
the client. For the configuration of such an address pool, refer to section
Creating a Static
Address Pool for the DHCP Server .
2. Otherwise, the DHCP server will select the smallest address pool that contains the IP address of
the receiving interface (if the client and the server reside on the same network segment), or the