A netmask is a 32-bit mask used to divide an IP address into
subnets and specify the networks available hosts. In a netmask,
two bits are always automatically assigned. For example, in
255.255.225.0, “0″ is the assigned network address; and in
255.255.255.255, “255″ is the assigned broadcast address. The 0
and 255 are always assigned and cannot be used. Because of VM
setup I couldn’t emulate this on back track but I used something
similar like this in ubuntu.