When using RFC1918 (IPv4) 20-bit block private address space, special caution is needed

For networks , the correct default netmask should be 
binary = 11111111 11110000 00000000 00000000  

Using a netmask other than [ CIDR block] may unintentionally mask out perfectly valid IP addresses.

For the networks:
Base address
Highest address
Number of IPv4 addresses is 1,048,576