Dhcp Address Pool - H3C S3610-28P Operation Manual

Operation Manual – DHCP
H3C S3610&S5510 Series Ethernet Switches

2.1.2 DHCP Address Pool

I. 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.
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 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 this
address pool, refer to section
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 in the same
network segment), or the smallest address pool that contains the IP address
specified in the giaddr field of the client's request (if a DHCP relay agent is
in-between). If no IP address is available in such address pool, the DHCP server
will fail to assign an address to the client because it cannot assign an IP address
from the father address pool to the client. For the configuration of such address
pool, refer to section
Configuring manual address
Configuring dynamic address
2-2
Chapter 2 DHCP Server Configuration
allocation.
allocation.