HP 4800G Series Configuration Manual page 294

The dhcp relay address-check enable command is independent of other commands of the
DHCP relay agent. That is, the invalid address check takes effect when this command is executed,
regardless of whether other commands are used.
The dhcp relay address-check enable command only checks IP and MAC addresses of clients.
You are recommended to configure IP address check on the interface enabled with the DHCP relay
agent; otherwise, the valid DHCP clients may not be capable of accessing networks.
When using the dhcp relay security static command to bind an interface to a static binding entry,
make sure that the interface is configured as a DHCP relay agent; otherwise, address entry
conflicts may occur.
Configuring dynamic binding update interval
Via the DHCP relay agent, a DHCP client sends a DHCP-RELEASE unicast message to the DHCP
server to relinquish its IP address. In this case the DHCP relay agent simply conveys the message to
the DHCP server, thus it does not remove the IP address from its bindings. To solve this problem, the
DHCP relay agent can update dynamic bindings at a specified interval.
The DHCP relay agent uses the IP address of a client and the MAC address of the DHCP relay interface
to periodically send a DHCP-REQUEST message to the DHCP server.
If the server returns a DHCP-ACK message or does not return any message within a specified
interval, which means the IP address is assignable now, the DHCP relay agent will update its
bindings by aging out the binding entry of the IP address.
If the server returns a DHCP-NAK message, which means the IP address is still in use, the relay
agent will not age it out.
Follow these steps to configure dynamic binding update interval:
To do...
Enter system view
Configure binding
update interval
Enabling unauthorized DHCP servers detection
There are unauthorized DHCP servers on networks, which reply DHCP clients with wrong IP
addresses.
With this feature enabled, upon receiving a DHCP request, the DHCP relay agent will record the IP
address of the DHCP server which assigned an IP address to the DHCP client and the receiving
interface. The administrator can use this information to check out any DHCP unauthorized servers.
Use the command...
system-view
dhcp relay security
tracker { interval | auto }
3-6
Remarks
—
Optional
auto by default. (auto interval is calculated by
the relay agent according to the number of
bindings.)