40-3Figure 40-2 Padding contents for sub-option 1 of Option 82Figure 40-3 Padding contents for sub-option 2 of Option 82anism of Option 82 supported on DHCP relay agentcedMechThe pro ure for a DHCP client to obtain an IP address from a DHCP server through a DHCP relaygent is similar to that for the client to obtain an IP address from a DHCP server directly. The followingchanism of Option 82 support on DHCP relay agent.1) Upon receiving a DHCP request, the DHCP relay agent checks whether the packet containsz If the request packet does not contain Option 82, the DHCP relay agent adds Option 82 to thepacket and forwards the packet to the DHCP server.2) Upon receiving the packet returned from the DHCP server, the DHCP relay agent strips Option 82DHCPclient.aare the meOption 82 and processes the packet accordingly.z If the request packet contains Option 82, the DHCP relay agent processes the packet dependingon the configured strategy (that is, discards the packet, replaces the original Option 82 in thepacket with its own, or leaves the original Option 82 unchanged in the packet), and forwards thepacket (if not discarded) to the DHCP server.from the packet and forwards the packet with the DHCP configuration information to theRequest packets sent by a DHCP client fall into two categories: DHCP-DISCOVER packets andDHCP-REQUEST packets. As DHCP servers coming from different manufacturers process DHCPSCOVERpackettrequest packets in different ways (that is, some DHCP servers process Option 82 in DHCP-DIs, whereas the rest process Option 82 in DHCP-REQUEST packets), a DHCP relay agent addsOp ion 82 to both types of packets to accommodate to DHCP servers of different manufacturers.DHCmessage from a DHCP client, the switch will replaceP Inform Message Handling Feature Used in XRN SystemSome DHCP clients, after obtaining IP addresses, send DHCP Inform messages to the DHCP server torequest other configuration parameters (such as DNS server and default gateway addresses).If an S4500 series switch belongs to a fabric, you need to enable UDP Helper and then DHCP relayagent on it. Then, upon receiving a DHCP Inform
