RE: Subnet masks. "However, in CIDR notation, the prefix bits are always contiguous, whereas subnet masks may specify non-contiguous bits. However, this has no practical advantage for increasing efficiency."

Also, a general note: "For routed subnets bigger than /31 or /32, two reserved addresses need to be subtracted from the number of available host addresses: the largest address, which is used as the broadcast address, and the smallest address, which is used to identify the network itself. It is also common for the IP gateway for that subnet to use an address, meaning that three addresses would have to be subtracted from the number of hosts that can be used on the subnet."