D-Link DNS-320L User Manual page 394

Section 5 - Knowledge Base
Under Mode, select Master from the drop-down list and then click Add.
Enter the IP address of the other UPS slave on the network.
Click the + button to add more IP addresses.
Make sure the DNS-320L and the UPS slaves are on the same physical
network.
Click OK to continue.
D-Link ShareCenter DNS-320L User Manual 388