594 CHAPTER 57: DHCP S ERVER CONFIGURATIONsegment or some subnets (such as domain name), you just need to configurethem on the network segment or the corresponding subnets. The following is thedetails of configuration inheritance.1 A newly created child address pool inherits the configurations of its parent addresspool.2 For an existing parent-child address pool pair, when you perform a newconfiguration on the parent address pool:■ The child address pool inherits the new configuration if there is nocorresponding configuration on the child address pool.■ The child address pool does not inherit the new configuration if there is alreadya corresponding configuration on the child address pool.DHCP IP AddressPreferencesInterfaces 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 addresspool mode, it picks IP addresses from the interface address pools and assigns themto the DHCP clients. If there is no available IP address in the interface addresspools, the DHCP server picks IP addresses from its global address pool thatcontains the interface address pool segment and assigns them to the DHCPclients.A DHCP server assigns IP addresses in interface address pools or global addresspools to DHCP clients in the following sequence:■ IP addresses that are statically bound to the MAC addresses of DHCP clients■ 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.■ The first IP address found among the available IP addresses in the DHCPaddress pool.■ If no IP address is available, the DHCP server queries lease-expired andconflicted IP addresses. If the DHCP server finds such IP addresses, it assignsthem; otherwise the DHCP server does not assign IP addresses.Global AddressPool-Based DHCPServer ConfigurationConfiguration Tasks Table 461 Global address pool-based DHCP server configuration tasksConfiguration task Description Related sectionEnable DHCP Required “Enabling DHCP”on page 595Configure global address pool mode oninterface(s)Optional “Configuring GlobalAddress Pool Modeon Interface(s)” onpage 595
