If you want the network or subnetwork to be defined in the networks table, then you must specify a name here.

Network names can be 2-255 alphanumeric characters, composed of uppercase and lowercase letters, the numbers 0-9, the minus sign (-), and the underbar (_). The first character cannot be a minus or underbar, and the name must be a minimum of 2 characters. Dots can be used in the middle of a name when it is separator for a qualified domain; for example bigmachine.bigcompany.