DHCP Security Configuration 137Customizing DHCPServiceWith the evolution of DHCP, new options are constantly coming into being. You canadd the new options as the properties of DHCP servers by performing the followingconfiguration.DHCP SecurityConfigurationDHCP security configuration is needed to ensure the security of DHCP service.Prerequisites Before configuring DHCP security, you should first complete the DHCP serverconfiguration (either global address pool-based or interface address pool-based DHCPserver configuration).Configuring PrivateDHCP Server DetectingA private DHCP server on a network also answers IP address request packets andassigns IP addresses to DHCP clients. However, the IP addresses they assigned mayconflict with those of other hosts and cause users cannot normally access networks.This kind of DHCP servers are known as private DHCP servers.With the private DHCP server detecting function enabled, a DHCP server tracks theinformation (such as the IP addresses and interfaces) of DHCP servers to enable theadministrator to detect private DHCP servers in time and take proper measures.Configuring IP AddressDetectingTo avoid IP address conflicts caused by assigning the same IP address to multipleDHCP clients simultaneously, you can configure a DHCP server to detect an IP addressbefore it assigns the address to a DHCP client.IP address detecting is achieved by performing ping operations. To detect whether ornot an IP address is currently in use, the DHCP server sends an ICMP (Internet ControlMessage Protocol) packet with the IP address to be assigned as the destination andwaits for a response. If the DHCP server receives no response within a specified time,it resends an ICMP packet. This procedure repeats on and on until the DHCP serverTable 126 Customize DHCP serviceOperation Command DescriptionEnter system view system-view -Configure customizedoptionsConfigure forthe currentinterfaceinterface interface-typeinterface-numberRequiredBy default, nocustomized optionis configured.dhcp server option code { asciiascii-string | hexhex-string&<1-10> | ip-addressip-address&<1-8> }quitConfigure formultipleinterfacesdhcp server option code { asciiascii-string | hexhex-string&<1-10> | ip-addressip-address&<1-8> } { interfaceinterface-type interface-number [to interface-typeinterface-number ] | all }Table 127 Enable private DHCP server detectingOperation Command DescriptionEnter system view system-view -Enable the private DHCPserver detecting functiondhcp serverdetectRequiredBy default, the private DHCP server detectingfunction is disabled.
