3Com WX3000 operation manual Dhcp-security static ip-address, Mac-address, Address-check enable

To do…	Use the command…	Remarks
Enter system view	system-view	—
Create a static	dhcp-security static ip-address	Optional
IP-to-MAC binding	mac-address	Not created by default.
Enter interface view	interface interface-type interface-number	—
Enable the address	address-check enable	Required
checking function		Disabled by default.

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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.

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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…	Use the command…	Remarks
Enter system view	system-view	—
Enable the DHCP relay agent	dhcp relay hand enable	Optional
handshake function		Enabled by default.

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