The IP Helper allows the SonicWall to forward DHCP requests originating from the interfaces on a SonicWall to a centralized DHCP server on the behalf of the requesting client. IP helper is used extensively in routed VLAN environments where a DHCP server is not available for each interface, or where the layer three routing mechanism is not capable of acting as a DHCP server itself. The IP helper also allows NetBIOS broadcasts to be forwarded with DHCP client requests.
In the SonicWall interface under Network |IP Helper:
IP Helper Settings -check Enable IP Helper.
Relay Protocols - check Enable for the DHCP protocol.
Policies - click add.
check Enable Policy.
Protocol: Select DHCP or NetBIOS from the protocol menu.
From: Select a source Interface or Zone from the From menu.
To: Select a destination IP address or subnet from the To menu.
Click OK to add the policy to the IP Helper policies table and Accept