Dell C9000 Series Networking Configuration Manual page 400

You can configure an interface on the Dell Networking system to relay the DHCP messages to a specific
DHCP server using the ip helper-address command from INTERFACE mode, as shown in the following
illustration. Specify multiple DHCP servers by using the ip helper-address command multiple times.
When you configure the ip helper-address command, the system listens for DHCP broadcast messages
on port 67. The system rewrites packets received from the client and forwards them via unicast to the DHCP
servers; the system rewrites the destination IP address and writes its own address as the relay device.
Responses from the server are unicast back to the relay agent on port 67 and the relay agent rewrites the
destination address and forwards the packet to the client subnet via broadcast or unicast, depending whether
the client has set or cleared the BROADCAST flag in the DHCP Client PDUs.
NOTE: DHCP Relay is not available on Layer 2 interfaces and VLANs.
Figure 35. Configuring a Relay Agent
Dynamic Host Configuration Protocol (DHCP) 400