since no special address for any special task is used, you need to treat all addresses for use by subnets and hosts. So the numbers start from 0, and thus you need to be careful with respect to “first” or “second” versus one or two. For example, if the hosts are numbered 0, 1, 2,…..Then the first host has the id 0 (not 1). Similarly, the second host is 1 (not 2). If these numbers were used for subnets, then the first subnet is 0, second subnet is 1, etc. And when we say subnet 2, that means third subnet, because we start from 0.
This is a note from professor.
Thank you for your help