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Chapter 3

Internet Protocols

values for each position--either 0 or 1--gives you 2

, or 4,294,967,296).

The disadvantage of the flat addressing scheme, and the reason it's not used
for IP addressing, relates to routing. If every address were unique, all routers
on the Internet would need to store the address of each and every machine on
the Internet. This would make efficient routing impossible, even if only a
fraction of the possible addresses were used.

The solution to this dilemma is to use a two- or three-level, hierarchical

addressing scheme that is structured by network and host, or network, sub-
net, and host.

This two- or three-level scheme is comparable to a telephone number. The

first section, the area code, designates a very large area. The second section,
the prefix, narrows the scope to a local calling area. The final segment, the
customer number, zooms in on the specific connection. IP addresses use the
same type of layered structure. Rather than all 32 bits being treated as a
unique identifier, as in flat addressing, a part of the address is designated as
the network address, and the other part is designated as either the subnet and
host, or just the node address.

Network Addressing

The network address uniquely identifies each network. Every machine 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 is the network address.

The node address is assigned to, and uniquely identifies, each machine on

a network. This part of the address must be unique because it identifies a par-
ticular machine--an individual--as opposed to a network, which is a group.
This number can also be referred to as a host address. In the sample IP
address 172.16.30.56, the 30.56 is the node address.

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 rank Class A network. At the
other extreme is the Class C network, which is reserved for the numerous
networks with a small number of nodes. The class distinction for net-
works between very large and very small is predictably called the Class B
network.

Subdividing an IP address into a network and node address is determined

by the class designation of one's network. Figure 3.10 summarizes the three
classes of networks--a subject I'll explain in much greater detail throughout
this chapter.

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