Review of IP Addressing
67
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 by
default.
The host 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.
In the sample IP address 172.16.30.56, .30.56 is the host address by
default.
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, 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. Subdividing an
IP address into a network and node address is determined by the class des-
ignation of a network. Table 3.1 provides a summary of the three classes of
networks, which will be described in much more detail throughout this
chapter.
To ensure efficient routing, Internet designers defined a mandate for the
leading bits section of the address for each network class. For example, since
a router knows that a Class A network address always starts with 0, the
T A B L E 3 . 1
The Three Classes of IP Addresses Used in Networks Today
Class
Leading
Bit
Pattern
Default
Subnet Mask
Address Range
Number of
Addresses
A
0
255.0.0.0
1.0.0.0126.0.0.0
16,777,214
B
10
255.255.0.0
128.1.0.0
191.254.0.0
65,534
C
110
255.255.255.0
192.0.1.0
223.255.254.0
254
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