3Com WX3000 Series Operation Manual page 322

To do...
Enter system view
Create a static
IP-to-MAC binding
Enter interface view
Enable the address
checking function
The 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 (such as the command to enable DHCP) are used.
Before executing the address-check enable command on the interface connected to the DHCP
server, you need to configure the static binding of the IP address to the MAC address of the DHCP
server. Otherwise, the DHCP client will fail to obtain an IP address.
Configuring the dynamic client address entry updating function
After relaying an IP address from the DHCP server to the DHCP client, the DHCP relay agent can
automatically record the client's IP-to-MAC binding and generate a dynamic address entry. But as a
DHCP relay agent does not process DHCP-RELEASE packets, which are sent to DHCP servers by
DHCP clients through unicast when the DHCP clients release IP addresses, the user address entries
maintained by the DHCP cannot be updated in time. You can solve this problem by enabling the DHCP
relay agent handshake function and configuring the dynamic client address entry updating interval.
After the handshake function is enabled, the DHCP relay agent sends the handshake packet (the
DHCP-REQUEST packet) periodically to the DHCP server using a client's IP address and its own MAC
address.
If the DHCP relay agent receives the DHCP-ACK packet from the DHCP server, or receives no
response from the server within a specified period, the IP address can be assigned. The DHCP
relay agent ages out the corresponding entry in the client address table.
If the DHCP relay agent receives the DHCP-NAK packet from the DHCP server, the lease of the IP
address does not expire. The DHCP relay agent does not age out the corresponding entry.
Follow these steps to configure the dynamic user address entry updating function:
To do...
Enter system view
Enable the DHCP relay agent
handshake function
Use the command...
system-view
dhcp-security static ip-address
mac-address
interface interface-type interface-number
address-check enable
Use the command...
system-view
dhcp relay hand enable
2-6
Remarks
—
Optional
Not created by default.
—
Required
Disabled by default.
Remarks
—
Optional
Enabled by default.