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Chapter 3
IP Addressing
Binary, as in 10101100.00010000.00011110.00111000
Hexadecimal, as in AC 10 1E 38
All of these examples represent the same IP address. Although hexadecimal is
not used as often as dotted-decimal or binary when IP addressing is dis-
cussed, you might find an IP address stored as hexadecimal in some pro-
grams. The 32-bit IP address is a structured, or hierarchical, address, as
opposed to a flat, or nonhierarchical, address. Although either type of
addressing scheme could have been used, the hierarchical variety was chosen
for a good reason.
The advantage of the hierarchical scheme is that it can handle a large
number of addresses, namely 4.2 billion (a 32-bit address space with two
possible values for each position--either 0 or 1--gives you approximately
4.2 billion). The disadvantage of the flat address 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 flat address dilemma is to use a two- or three-level
hierarchical addressing scheme that is structured by network and host or by
network, subnet, and host. A two- or three-level hierarchy is comparable to
the sections of a telephone number. The first section, the area code, desig-
nates 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 address-
ing, one part of the address is designated as the network address, and the
other part is designated as either the subnet or host address. Note that in
some literature, the host address may be referred to as the node address.
In the following sections, we will discuss network addressing and the
three different address classes:
Class A addresses
Class B addresses
Class C addresses
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