Administrator Guide

Debugging the DHCP Server
To debug the DHCP server, use the following command.
● Display debug information for DHCP server.
EXEC Privilege mode
debug ip dhcp server [events | packets]
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
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 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.
330 Dynamic Host Configuration Protocol (DHCP)