D-Link DSL-2640B - Manual (Page 14)

13
Device Setup
You can configure the DSL Router IP address and Subnet Mask for the LAN interface
to correspond to your LAN’s IP Subnet. If you want the DHCP server to
automatically assign IP addresses, then enable the DHCP server and enter the range
of IP addresses that the DHCP server can assign to your computers. Disable the
DHCP server if you would like to manually assign IP addresses. Click on Next to
continue.