Operation Manual – DHCPH3C S7500 Series Ethernet Switches Chapter 2 DHCP Server Configuration2-2z If an interface is configured with a valid unicast IP address, you can create aninterface-based address pool for the interface by executing the dhcp selectinterface command in interface view. The IP addresses an interface addresspool holds belong to the network segment the interface resides in and areavailable to the interface only.II. The structure of an address poolThe address pools of a DHCP server are hierarchically organized in a tree-likestructure. The root holds the IP addresses of the network segment, the branches holdthe subnet IP addresses, and the leaves hold the IP addresses that are manuallybound to specific clients. The address pools that are of the same level are sorted bytheir configuration precedence order. Such a structure enables configurations to beinherited. That is, the configurations of the network segment can be inherited by itssubnets, whose configurations in turn can be inherited by their client address. So, forthe 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 orthe corresponding subnets. The following is the details of configuration inheritance.1) A newly created child address pool inherits the configurations of its parentaddress pool.2) For an existing parent-child address pool pair, when you perform a newconfiguration on the parent address pool:z The child address pool inherits the new configuration if there is no correspondingconfiguration on the child address pool.z The child address pool does not inherit the new configuration if there is already acorresponding configuration on the child address pool.2.1.3 DHCP IP Address PreferencesInterfaces of the DHCP server can work in the global address pool mode or in theinterface address pool mode. If the DHCP server works in the interface address poolmode, it picks IP addresses from the interface address pools and assigns them to theDHCP clients. If there is no available IP address in the interface address pools, theDHCP server picks IP addresses from its global address pool that contains theinterface address pool segment and assigns them to the DHCP clients.A DHCP server assigns IP addresses in interface address pools or global addresspools to DHCP clients in the following sequence:z IP addresses that are statically bound to the MAC addresses of DHCP clientsz IP addresses that are ever used by DHCP clients. That is, those in the assignedleases recorded by the DHCP server. If there is no record in the leases and theDHCP-DISCOVER packets sent by DHCP clients contain option 50 fields, theDHCP server assigns the IP address requested by option 50.
