Understanding IPv

IP addresses used with IPv4 can be divided into two parts: the network ID and the host ID. The network ID identifies the network on which a computer or device is located and the host ID identifies the computer or device.

An example of an IPv4 address is, which shows the four distinct sets of numbers divided by a period, or dot. Each section separated by a dot is referred to as an octet, which correlates to an eight-bit number in binary form.

The second set of numbers associated with an IPv4 address is the subnet mask. The subnet mask identifies which parts of the IP address belong to the network ID and which parts belong to the host ID.

Subnet masks use four distinct octets separated by a period, or dot, just like the IP address. Subnet masking correlates to the network ID and the actual host ID of the computer by giving binary values of either a 1, for a bit that belongs to the network ID, or 0, for a bit that belongs to the host ID. An example of a subnet mask is, which is read in binary as 11111111.00000000.00000000.00000000. Thus, the first 8 bits of the IP address belong to the network ID and the final 24 bits belong to the host ID.

When you use standard subnet masks, you are said to be using a classful network. Classful networks are defined in three different classes: Class A, Class B, and Class C. Table 14-2 shows examples of the different classful networks. Table 14-3 shows network ID examples, and Table 14-4 gives some examples of subnet forms translated into binary to help you understand the differences in their formats and to differentiate the network ID portion of the subnet from the host ID portion of the subnet.

Table 14-2. IPv4 subnet example

Subnet class


Maximum nodes

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