Configuring the DHCP Server

If you want to use the Dell SonicWALL Security Appliance’s DHCP server, select Enable DHCP Server on the Network > DHCP Server page.

The following DHCP server options can be configured:

•	Select Enable Conflict Detection to turn on automatic DHCP scope conflict detection on each zone.

Compatible with Conflict Detection – Currently, DHCP server performs server-side conflict detection when this feature is enabled. The advantage of server-side conflict detection is that it detects conflicts even when the DHCP client does not run client-side conflict detection. However, if there are a lot of DHCP clients on the network, server-side conflict detection can result in longer waits for a full IP address allocation to complete.

NOTE: Conflict detection is not performed for an IP address that belongs to a “relayed” subnet scope. The DHCP server only performs a conflict detection ICMP check for a subnet range attached to its interface.

•	Select Enable DHCP Server Persistence to allow the current state of the DHCP leases in the network to be periodically written to Flash. At reboot, the system restores the previous DHCP server network DHCP allocation knowledge based on the IP.Lease times stored in Flash.

•	DHCP Server Persistence Monitoring Interval: Controls how often changes in the network are examined and, if necessary, written to Flash. Specify the time in minutes. The default is 5 minutes.

NOTE: Decreasing this setting below 5 minutes may reduce the overall read/write lifetime of the Flash component.

To configure Option Objects, Option Groups, and Trusted Agents, click the Advanced button. For detailed information on configuring these features, see Configuring Advanced DHCP Server Options .

Configuring DHCP Server Persistence

DHCP server persistence is the ability of the firewall save DHCP lease information and to provide the client with a predictable IP address that does not conflict with another use on the network, even after a client reboot.

DHCP server persistence works by storing DHCP lease information periodically to flash memory. This ensures that users have predicable IP addresses and minimizes the risk of IP addressing conflicts after a reboot.

DHCP server persistence provides a seamless experience when a user reboots a workstation. The DHCP lease information is saved, and the user retains the same workstation IP address. When a firewall is restarted, usually due to maintenance or an upgrade, DHCP server persistence provides the following benefits:

•	IP address uniqueness: Lease information is stored in flash memory, so the risk of assigning the same IP address to multiple users is nullified.

•	Ease of use: By saving the lease information in the flash memory, the user’s connections are automatically restored.

To configure DHCP Server Persistence, select the Enable DHCP Server Persistence checkbox. Optionally, you can modify how often the DHCP server stores DHCP lease information by modifying the DHCP Server Persistence Monitoring Interval field. The default is 5 minutes.