Sizes of Network and Host Parts of IP Addresses
|
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) |
224 2, or 16,777,214 |
|
B |
2 (16) |
2 (16) |
216 2, or 65,534 |
|
C |
3 (24) |
1 (8) |
28 2, or 254 |
Class A networks have 1 octet (byte) in the network part of the
address, and 3 octets in the host part. Because you can have any values in the
host part of the address, you can have 224 different IP addresses
that all start with the same number in the first octet. Of those 224
addresses, two are reserved. So, each Class A network has a ton of addressesmore
than 16 million.
Each Class B network requires that all addresses in the network
use the same first 2 octets. That means the network part of these addresses is 2
octets long, leaving only 2 octets for the host part. Because the host part can
have any value in it (except the two reserved values), you can have
2162 host addresses in each Class B network.
Similarly, Class C networks have 3 octets in the network part
of the addresses, meaning that every address in one Class C network must have
the same value in the first 3 octets. That leaves 1 octet as the host part,
implying 282, or 254, host addresses per Class C network.
Figure 10-7 shows the
same network diagram as in Figure 10-6,
but this time with three different classes of IP network numbers shown.
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