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Chapter 3

Internet Protocols

Class B Addresses

In a Class B network address, the first two bytes are assigned to the network
address, and the remaining two bytes are used for node addresses. The
format is:

network.network.node.node

For example, in the IP address 172.16.30.56, the network address is 172.16,
and the node address is 30.56.

With a network address being two bytes (eight bits each), there would be

unique combinations. But the Internet designers decided that all Class B

network addresses should start with the binary digit 1, then 0. This leaves 14
bit positions to manipulate, therefore 16,384 (that is, 2

) unique Class B net-

work addresses.

A Class B address uses two bytes for node addresses. This is 2

minus the

two reserved patterns (all 0s and all 1s), for a total of 65,534 possible node
addresses for each Class B network.

Class B Valid Host IDs

Here's an example of how to find the valid hosts in a Class B network:

All host bits turned off is the network address: 172.16.0.0.

All host bits turned on is the broadcast address: 172.16.255.255.

The valid hosts would be the numbers in between the network address

and the broadcast address: 172.16.0.1 through 172.16.255.254.

Class C Addresses

The first three bytes of a Class C network address are dedicated to the net-
work portion of the address, with only one measly byte remaining for the
node address. The format is

network.network.network.node

Using the example IP address 192.168.100.102, the network address is

192.168.100, and the node address is 102.

In a Class C network address, the first three bit positions are always the

binary 110. The calculation is such: 3 bytes, or 24 bits, minus 3 reserved
positions, leaves 21 positions. Hence, there are 2

, or 2,097,152, possible

Class C networks.

Each unique Class C network has one byte to use for node addresses. This

leads to 2

or 256, minus the two reserved patterns of all 0s and all 1s, for a

total of 254 node addresses for each Class C network.

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