D-Link DI-1162 - Manual (Page 154)

DI-1162 Remote Access Router
144 Appendix C - IP Concepts
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.