Reference Guide

Using DHCP Clear Commands
To clear DHCP binding entries, address conflicts, and server counters, use the following commands.
• 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
This feature is available on the S4820T platform.
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.
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