11 DHCP RELAY C ONFIGURATIONIntroduction to DHCPRelayThis section contains an introduction to DHCP RelayUsage of DHCP Relay Early DHCP implementations assumes that DHCP clients and DHCP servers are on thesame network segment, that is, you need to deploy at least one DHCP server for eachnetwork segment, which is far from economical.DHCP Relay is designed to address this problem. It enables DHCP clients of multiplenetworks to share a common DHCP server, through which DHCP clients in a LAN canacquire IP addresses by negotiating with DHCP servers of other networks. It decreasesyour cost and provides a centralized administration.A DHCP relay can be a host or a switch that has DHCP relay service enabled.DHCP RelayFundamentalsFigure 35 illustrates a typical DHCP relay application.Figure 35 Typical DHCP relay applicationA DHCP relay works as follows:■ A DHCP client broadcasts a configuration request packet in the local networkwhen it starts and initiates.■ If a DHCP server exists in the local network, it processes the configuration requestpacket directly without the help of a DHCP relay.■ If no DHCP server exists in the local network, the network device serving as aDHCP relay on this network appropriately processes the configuration requestpacket and forwards it to a specified DHCP server located on another network.■ When the DHCP server receives the packet, it generates configuration informationaccordingly and sends it to the DHCP client through the DHCP relay to completethe dynamic configuration of the DHCP client.Note that such an interacting process may be repeated several times for a DHCP clientto be successfully configured.
