Dhcp Ip Address Preferences - Huawei Quidway S3900 Series Operation Manual

Operation Manual - DHCP
Quidway S3900 Series Ethernet Switches-Release 1510
If an interface is configured with a valid unicast IP address, you can create an
interface-based address pool for the interface by executing the dhcp select
interface command in interface view. The IP addresses an interface address pool
holds belong to the network segment the interface resides in and are available to
the interface only.
II. The structure of an address pool
The address pools of a DHCP server are hierarchically organized in a tree-like
structure. The root holds the IP address of the network segment, the branches hold
the subnet IP addresses, and the leaves holds the IP addresses that are manually
bound to specific clients. The address pools that are of the same level are sorted by
their configuration precedence order. Such a structure enables configurations to be
inherited. That is, the configurations of the network segment can be inherited by its
subnets, whose configurations in turn can be inherited by their client address. So, for
the parameters that are common to the whole network segment or some subnets
(such as domain name), you just need to configure them on the network segment or
the corresponding subnets. The following is the details of configuration inheritance.
A newly created child address pool inherits the configurations of its parent
address pool.
For an existing parent-child address pool pair, when you performs a new
configuration on the parent address pool:
The child address pool inherits the new configuration if there is no corresponding
configuration on the child address pool.
The child address pool does not inherit the new configuration if there is already a
corresponding configuration on the child address pool.

2.1.4 DHCP IP Address Preferences

Interfaces of the DHCP server can work in the global address pool mode or in the
interface address pool mode. If the DHCP server works in the interface address pool
mode, it picks IP addresses from the interface address pools and assigns them to the
DHCP clients. If there is no available IP address in the interface address pools, the
DHCP server picks IP addresses from its global address pool that contains the
interface address pool segment and assigns them to the DHCP clients.
A DHCP server assigns IP addresses in interface address pools or global address
pools to DHCP clients in the following sequence:
IP addresses that are statically bound to the MAC addresses of DHCP clients or
client IDs
IP addresses that are ever used by DHCP clients. That is, those in the assigned
leases recorded by the DHCP server. If there is no record in the leases and the
DHCP-DISCOVER packets sent by DHCP clients contain option 50 fields, the
DHCP server assigns the IP address requested by option 50.
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Chapter 2 DHCP Server Configuration