Dell S4048T Configuration Manual page 352

in the following illustration. Specify multiple DHCP servers by using the ip helper-address dhcp-
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 on the Z-Series and S4820T
platforms. DHCP relay agent is supported on Layer 2 interfaces and VLANs on the S3048–ON, S4810 and
S4048–ON platforms.
Figure 39. Configuring a Relay Agent
Dynamic Host Configuration Protocol (DHCP) 352