Dell S4820T, Configuration Manual

Page: 340 / 1178

• Clear DHCP binding entries for the entire binding table.
EXEC Privilege mode.
clear ip dhcp binding
• Clear a DHCP binding entry for an individual IP address.
EXEC Privilege mode.
clear ip dhcp binding ip address
Configure the System to be a Relay Agent
DHCP clients and servers request and offer configuration information via broadcast DHCP messages.
Routers do not forward broadcasts, so if there are no DHCP servers on the subnet, the client does not
receive a response to its request and therefore cannot access the network.
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 dhcp-address
command from INTERFACE mode, as
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.
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Dynamic Host Configuration Protocol (DHCP)