Wiki's article pertains to the network topology.
D-Link wrote:
Use Unicasting: This option is normally turned off, and should remain off as long as the WAN-side DHCP server correctly provides an IP address to the router. However, if the router cannot obtain an IP address from the DHCP server, the DHCP server may be one that works better with unicast responses. In this case, turn the unicasting option on, and observe whether the router can obtain an IP address. In this mode, the router accepts unicast responses from the DHCP server instead of broadcast responses.
The network topology (routing) is being handle by the DIR-655, not my Cable Modem SB6121.
I remain in the state of being confused, in other words.
Mark.