Operation Manual – DHCPH3C S3610&S5510 Series Ethernet Switches Chapter 2 DHCP Server Configuration2-22.1.2 DHCP Address PoolI. Address pool structureIn response to a client’s request, the DHCP server selects an idle IP address from anaddress pool and sends it together with other parameters such as lease and DNSserver address to the client.The address pool database is organized as a tree. The root of the tree is the addresspool for natural networks, branches are address pools for subnets, and leaves areaddresses statically bound to clients. For the same level address pools, a previouslyconfigured pool has a higher selection priority than a new one.At the very beginning, subnetworks inherit network parameters and clients inheritsubnetwork parameters. Therefore, common parameters, for example a DNS serveraddress, should be configured at the highest (network or subnetwork) level of the tree.After establishment of the inheritance relationship, the new configuration at the higherlevel (father) of the tree will be:z Inherited if the lower level (child) has no such configuration, orz 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 poolThe DHCP server observes the following principles to select an address pool to assignIP addresses to clients:1) If there is an address pool where an IP address is statically bound to the MACaddress or ID of the client, the DHCP server will select this address pool andassign the statically bound IP address to the client. For the configuration of thisaddress pool, refer to section Configuring manual address allocation.2) Otherwise, the DHCP server will select the smallest address pool that contains theIP address of the receiving interface (if the client and the server reside in the samenetwork segment), or the smallest address pool that contains the IP addressspecified in the giaddr field of the client’s request (if a DHCP relay agent isin-between). If no IP address is available in such address pool, the DHCP serverwill fail to assign an address to the client because it cannot assign an IP addressfrom the father address pool to the client. For the configuration of such addresspool, refer to section Configuring dynamic address allocation.
