The Internet is based on client/server model. For example, a host may need to contact a DHCP (Short for Dynamic Host Configuration Protocol) server for obtaining its IP address. The requests are usually sent as broardcast messages. Since routers do not forward broadcasts, the DHCP server must be located in the same subnet as that of the client requesting the service. But, practical reasons may prohibit a DHCP server to be placed on each subnet of a network. One workaround to this problem is IP helper address. A router, configured with IP helper address can unicast the broadcast message received from a client (or host) in one subnet to a given IP address (of the server) in another subnet, which in turn provides the DHCP information to the client computer.
IP helper addresses can also be used for any other requests such as DNS requests or to locate TFTP servers on a network. IP helper address enables a network administrator to centralize the server services, such as DHCP service or DNS service.
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