TCP/IP Guide

IP Addresses with Special Meanings

Some IP addresses do not refer directly to specific hardware devices; instead, they are used to refer indirectly to one or more devices. To draw an analogy with language, most IP addresses refer to proper nouns, like "John" or "the red table in the corner." However, some are used more the way you use pronouns such as "this one" or "that group over there." I call these IP addresses with special meanings.

These special addresses are constructed by replacing the normal network ID or host ID (or both) in an IP address with one of two special patterns:

All Zeros When the network ID or host ID bits are replaced by a set of all zeros, the special meaning is the equivalent of the pronoun this, referring to whatever was ...