34Figure 10 DHCP relay agent work processAs shown in Figure 10, the DHCP relay agent works as follows:1. After receiving a DHCP-DISCOVER or DHCP-REQUEST broadcast message from a DHCP client, theDHCP relay agent fills the giaddr field of the message with its IP address and forwards the messageto the designated DHCP server in unicast mode.2. Based on the giaddr field, the DHCP server returns an IP address and other configurationparameters to the relay agent, which conveys them to the client.DHCP relay agent support for Option 82Option 82 records the location information of the DHCP client. The administrator can locate the DHCPclient to further implement security control and accounting. Table 2.If the DHCP relay agent supports Option 82, it handles a client’s request according to the contentsdefined in Option 82, if any. The handling strategies are described in Table 2.If a reply returned by the DHCP server contains Option 82, the DHCP relay agent removes the Option 82before forwarding the reply to the client.Table 2 DHCP relay agent and Option 82If a client’srequesting messagehas…HandlingstrategyPadding format The DHCP relay agent will…Option 82Drop Random Drop the message.Keep Random Forward the message without changingOption 82.ReplacenormalForward the message after replacing theoriginal Option 82 with the Option 82padded in normal format.verboseForward the message after replacing theoriginal Option 82 with the Option 82padded in verbose format.
