The 4 byte internet address consists of 2 parts, the network part
and the host part.
The network part is the same for all hosts connected to the
same network. The network part is used to route datagrams across
the Internet.
Every network in the global Internet has a unique network
identification number.
The host part must be unique within each specific network. It
is used to deliver the datagram once it has been routed to the
appropriate network.
The combination of the unique network number plus a
"host-within-network" number means that every Internet-connected
computer has a globally unique IP address.