D-Link DSL-500T - Manual (Page 79)

DSL-500T ADSL Router User’s Guide
67
Subnet Mask
In the absence of subnetworks, standard TCP/IP addressing may be used by specifying subnet masks as shown
below.
IP Class Subnet Mask
Class A 255.0.0.0
Class B 255.255.0.0
Class C 255.255.255.0
Subnet mask settings other than those listed above add significance to the interpretation of bits in the IP address.
The bits of the subnet mask correspond directly to the bits of the IP address. Any bit an a subnet mask that is to
correspond to a net ID bit in the IP address must be set to 1.