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IP Addressing and Subnetting 237
of the address. So, 2
16
possible addresses exist in a single Class B network. Finally, Class C
networks have a 3-byte-long network part, leaving only 8 bits for the host part, which implies
only 2
8
addresses in a Class C network. Table 5-9 summarizes the characteristics of Class A, B,
and C networks.
*
There are two reserved host addresses per network.
For example, Figure 5-17 shows a small network with addresses filled in. Network 8.0.0.0 is a
Class A network; Network 130.4.0.0 is a Class B network; Network 199.1.1.0 is a Class C
network.
Figure 5-17
Sample Network Using Class A, B, and C Network Numbers
Network numbers look like addresses (in dotted decimal format), but they are not assignable to
any interface as an IP address. Conceptually, network numbers represent the group of all IP
addresses in the network. Numerically, the network number is built with a nonzero value in the
network part but with all 0s in the host part of the network number. Given the three examples
from Figure 5-17, Table 5-10 provides a closer look at the numerical version of the three
network numbers: 8.0.0.0, 199.1.1.0, and 130.4.0.0.
Table 5-9
Sizes of Network and Host Parts of IP Addresses with No Subnetting
Any Network of
This Class
Number of
Network Bytes
(Bits)
Number of Host
Bytes (Bits)
Number of Addresses per
Network*
A
1 (8)
3 (24)
2
24
minus two special cases
B
2 (16)
2 (16)
2
16
minus two special cases
C
3 (24)
1 (8)
2
8
minus two special cases
Network
8.0.0.0
Network
130.4.0.0
Network
199.1.1.0
ch05.fm Page 237 Monday, March 20, 2000 5:06 PM