Network Addressing

Network Addressing
The network address collectively identifies each network. Every interface on the same network
shares that network address as part of its IP address. In the IP address 172.16.30.56, for example,
172.16.0.0 is the network address, by default, because of the classful boundary.
The host address singularly identifies each interface on a network segment. This part of the
address must be unique because it identifies a particular interface—an individual—as opposed
to a network, which is a group. Of course, host addresses may be duplicated across subnet
boundaries. Otherwise, IP address space would be grossly limited. Nevertheless, when the entire
32-bit IP address is taken as a unit, by combining the network and host portions, it becomes
unique across the accessible internetwork.
In the sample IP address 172.16.30.56, 30.56 is the host address because of the default
Class B boundary.
The designers of the Internet decided to create classes of networks based on network size. For
the small number of networks possessing a very large number of nodes, they created the Class A
network. At the other extreme is the Class C network, reserved for the numerous networks with
a small number of nodes. The class distinction for networks between very large and very small
is predictably called a Class B network. The default division of an IP address into a network and
node address is determined by the class designation of a network. Table 2.1 provides a summary
of the three classes of networks, which will be described in much more detail throughout this
chapter, plus special classes D and E.