The document provides an introduction to IPv4, which is the most common network addressing scheme currently deployed. It is a 32-bit binary addressing system that functions at the network layer of the OSI model. IPv4 addresses are divided into four classes: Class A addresses range from 0.0.0.0 to 127.255.255.255, Class B from 128.0.0.0 to 191.255.255.255, Class C from 192.0.0.0 to 223.255.255.255, and multicast Class D addresses from 224.0.0.0 to 239.255.255.255. Only Class D addresses do not have a clearly defined subnet mask.

1. Introduction to
IPv4 I.

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– Introducing IPv4.
– IPv4 address classes.
PACE-IT.

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Introduction to IPv4 I.

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Internet Protocol v.4 (IPv4)
is a binary addressing
scheme that is used for
networking. It was finalized
as a standard in 1981.
IPv4 is the most common network addressing
scheme that is deployed today. There is an issue
though. Because of its structure and the growth in
popularity of the Internet, most of the world has run
out of assignable IPv4 addresses. Thanks to some
forethought though, it is still a valid scheme.
Introduction to IPv4 I.

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– IPv4 works at Layer 3 of the OSI model.
» Layer 3 of the Open Systems Interconnection (OSI) model is
the network layer and its major focus is logical network and
host addressing. IPv4’s job is to provide the logical network and
host addresses.
– IPv4 is a 32-bit binary addressing scheme.
» The 32 bits are broken down into 4 octets (8 bits), which can be
represented by 0s and 1s.
» For human readability, it is represented in a format that is
called dotted decimal.
– There are theoretically 4,294,967,296
possible individual IPv4 addresses.
» Binary numbering uses base 2 counting, which means that
every bit that is present represents an exponential growth in the
value. So with IPv4 being a 32-bit number, the possible
maximum value is equal to 232.
Introduction to IPv4 I.

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– IPv4 address structure.
» Some of the bits make up the logical network address.
• Think of your own physical address.
» Some of the bits make up the logical host portion.
• Think of a letter that is addressed to you at your physical
address. Each address needs to be unique.
» A device called a subnet mask is used to determine which
portion of the IPv4 address is for the network and which part is
used for the host.
– The subnet mask.
» It is also a 32-bit binary number.
» It uses two methods of being represented (dotted decimal and
CIDR).
» If the subnet mask is used, it is applied bit by bit from left to
right.
• 11111111.00000000.00000000.00000000 = 255.0.0.0.
» Any portion of the IPv4 address that is covered by the 1s in the
subnet mask make up the logical network portion of the
address. The other portion makes up the host address.
Introduction to IPv4 I.

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Introduction to IPv4 I.

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– IPv4 has been divided into classes of
addresses.
» Class A addresses: (have a subnet mask of 255.0.0.0)
• 256 = the possible number of Class A networks.
• First octet always begins with a 0 (0xxxxxxx).
• Address range of 0.0.0.0 to 127.255.255.255.
» Class B addresses: (have a subnet mask of 255.255.0.0).
• 65,536 = the possible number of Class B networks.
• First octet always begins with a 10 (10xxxxxx).
• Address range of 128.0.0.0 to 191.255.255.255.
» Class C addresses: (have a subnet mask of 255.255.255.0).
• 16,777,216 = possible number of Class C networks.
• First octet always begins with a 110 (110xxxxx).
• Address range of 192.0.0.0 to 223.255.255.255.
» Class D addresses: (do not have a defined subnet mask).
• Class D addresses are special; they are used for multicast
network transmissions.
• First octet always begins with 1110 (1110xxxx).
• Address range of 224.0.0.0 to 239.255.255.255.
Introduction to IPv4 I.

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Introduction to IPv4 I.
IPv4 is currently the most common networking address scheme. It is a 32-
bit binary addressing scheme that functions at Layer 3 of the OSI model. It
is represented in a dotted decimal format to make it more human friendly.
Theoretically, it provides over four billion unique IP addresses. A portion of
the address represents the network ID and the other portion is used for the
host ID. A subnet mask is used to determine which part is which.
Topic
Introducing IPv4.
Summary
IPv4 has four classes of addresses. Class A addresses: 0.0.0.0 to
127.255.255.255. Class B addresses: 128.0.0.0 to 191.255.255.255. Class
C addresses: 192.0.0.0 to 223.255.255.255. Class D addresses: 224.0.0.0
to 239.255.255.255. Only Class D addresses do not have a clearly defined
subnet mask.
IPv4 address classes.

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THANK YOU!

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