If only one argument is present, it is taken as a host address or a host address with wild card. Here is a brief description. Binary representation is what we will need to determine network addresses and netmasks. Each network IP address is contained of network and host part. Generally speaking, networks are split into several classes.
First octet is network address while other three octets specify the host part.
First two octets are the network address, and third and fourth are host address. First three octets are the network address, and fourth is host address. Nothing stops us to divide the network given to us by a service provider into a several smaller networks. This is often done in real life. Network is being partitioned by setting the 32-bit subnet mask in which 1's represent the network part, and 0's represent the host part if IP address.