132 | DHCPw w w . d e l l . c o m | s u p p o r t . d e l l . c o m Figure 8-92. Using the show ip dhcp server statistics CommandUsing the Switch as a BootP/DHCP Relay AgentThe S-Series also can serve as a BootP/DHCP relay agent, forwarding DHCP packets between clients anda DHCP server (you can only use the switch as a relay agent to one DHCP server). This section describesthe concepts and tasks needed to configure the DHCP relay agent.DHCP Relay Agent OverviewWhen the switch is configured to act as a DHCP relay agent, it forwards DHCP client broadcasted requeststo a DHCP server on another broadcast domain (Layer 3 network). These broadcasted requests from aDHCP client use a destination IP address of 255.255.255.255 (all networks broadcast address).The DHCP relay agent process is as follows:1. The DHCP relay agent makes these two changes to the in-bound DHCP packet:a The relay agent appends its own IP address to the source IP address of the DHCP framesgoing to the DHCP server.b The relay agent populates the Gateway IP address field with the IP address of the interfaceon which the DHCP message is received from the client.2. The relay agent forwards the rewritten DHCP request on behalf of a DHCP client to the DHCP server.3. The DHCP server unicasts a reply to the DHCP relay agent, using the Gateway IP address field todetermine the subnet from which the DHCPDISCOVER, DHCPREQUEST, or DHCPINFORMmessage originated.4. The relay agent forwards the packet to the DHCP client.Force10 #show ip dhcp server statisticsAutomatic Bindings............................. 0Expired Bindings............................... 0Malformed Bindings............................. 0Messages Received---------- ----------DHCP DISCOVER.................................. 5DHCP REQUEST................................... 0DHCP DECLINE................................... 0DHCP RELEASE................................... 0DHCP INFORM.................................... 0Messages Sent---------- ------DHCP OFFER..................................... 0DHCP ACK....................................... 0DHCP NACK...................................... 0
