Dell S4820T Configuration Manual page 323

shown 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 38. Configuring a Relay Agent
Dynamic Host Configuration Protocol (DHCP)
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