5.2. The IPv4 Protocol

The IPv4 protocol assigns each device which is connected to the network a 32 bits number (IP address), which should identify it uniquely.
The problem is that large ranges in the IP "address-space" are reserved for different usages, or assigned to organizations which don't use even a small part of the range .
Therefore, a new standard for the Network Layer, called IPv6, which has a much larger address space, has been created, and is fully supported by Linux, but it is not commonly used yet.