H3C S9500 Series Operation Manual page 32

Operation Manual – DHCP
H3C S9500 Series Routing Switches
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 the domain
name, 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 of the tree will be:
Inherited if the lower level has no such configuration, or
Overridden if the lower level has such configuration.
Note:
The IP address lease does not have any inheritance.
II. Principles for selecting an address pool
The DHCP server observes the following principles to select an address pool to assign
IP addresses to clients:
1) If there is an address pool where IP addresses are statically bound to the MAC
addresses or IDs of clients, the DHCP server will select this address pool and
assign statically bound IP addresses to clients. For the configuration of this
address pool, refer to section
2) Otherwise, the DHCP server will select the smallest address pool that contains the
IP address of the interface receiving DHCP requests, regardless of the mask. If no
IP address is available in the smallest address pool, the DHCP server will fail to
assign addresses to clients because it will not assign those in the father address
pool to clients. For the configuration of the smallest address pool, refer to section
2.5.3 II. "Configuring dynamic address
For example, two address pools are configured on the DHCP server. The ranges of IP
addresses that can be dynamically assigned are 1.1.1.0/24 and 1.1.1.0/25 respectively.
If the IP address of the interface receiving DHCP requests is 1.1.1.1/25, the DHCP
server will select IP addresses for clients from the 1.1.1.0/25 address pool. If no IP
address is available in the 1.1.1.0/25 address pool, the DHCP server will fail to assign
addresses to clients. If the IP address of the interface receiving DHCP requests is
1.1.1.130/25, the DHCP server will select IP addresses for clients from the 1.1.1.0/24
address pool.
Chapter 2 DHCP Server Configuration
2.5.3 I. "Configuring manual address
allocation".
2-2
allocation".