 what are these special values let us look at them. So, how subnet mask work is they use the binary form of a subnet mask, do a logical operation with the IP address and then try to determine the network address, but to do that what is very essential for a subnet mask is to have the trailing set of ones. So, a subnet mask can only take values which are trailing ones and in continuation let us look at some of the other type of subnet masks. So, another subnet mask here is 255, 255, 255, 0 which we just saw. So, it has a 8 plus 8 plus 8 that is 24 trailing ones. Similarly, a subnet mask of 255, 0.0, 0.0 has a 8 trailing ones. Similarly, a subnet mask of 255, 255, 255, 252 would have a total of 30 trailing ones. So, using these different type of subnet mask, how can you calculate the number of IP addresses that are available.