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Extending IP Addresses

Using the example IP address 192.168.100.102, the network address is
192.168.100, and the host address is 102.

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

110. The calculation is as follows: 3 bytes, or 24 bits, minus 3 reserved posi-
tions, equals 21 positions. There are, therefore, 221, or 2,097,152, possible
Class C networks.

Each unique Class C network uses one byte for node addresses. This leads

to 28, or 256, minus the two reserved patterns of all zeros and all ones, for
a total of 254 node addresses for each Class C network.

Here is an example of how to find a valid host ID in a Class C network:

192.168.100.0 All host bits turned off is the network ID.

192.168.100.1 The first host.

192.168.100.254 The last host.

192.168.100.255 All host bits turned on is the broadcast address.

Extending IP Addresses

n the "old days," when the Network Information Center (NIC)

assigned a network number to an organization, it either assigned the first
octet (a Class A network), the first two octets (a Class B network), or the
first three octets (a Class C network). The organization could take this one
network number and further subdivide it into smaller networks through a
process called subnetting.

To illustrate, let's say that our organization has been assigned the Class B

network 172.16.0.0. We have several different network segments, each of
which needs a unique network number. So, we decide to subnet our network.
We use a subnet mask of 255.255.255.0. The subnet mask determines which
portion of our IP address belongs to the network portion and which part
belongs to the host portion. If we write our subnet mask out in binary, as
illustrated in Table 3.3, the ones correspond to the network portion of the
address, and the zeros correspond to the node portion of the address.

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