The document explains IP addresses, their classes, and subnetting. It details the two main types of IP addresses, IPv4 and IPv6, and outlines the importance of subnetting for network efficiency and security. Additionally, it categorizes IP addresses into classes A, B, C, D, and E, explaining their characteristics and typical usage scenarios.

1. IP Addresses & Its
Classes
Prepared By:
Aditi Nandi Tokder
Assistant Professor
ECE Department
Techno Main Salt Lake

2. Content
Introduction
1
Subnetting & Subnet Mask
2
Classes of IP Addresses
3

3. Introduction
An Internet Protocol (IP) address is the unique identifying number assigned to every device connected to the internet.
Computers that communicate over the internet or via local networks share information to a specific location using IP
addresses.
There are two main types of IP addresses: IPv4 and IPv6
IPv4 addresses are 32-bit integers that have to be expressed in Decimal Notation. It is represented by 4 numbers
separated by dots in the range of 0-255, which have to be converted to 0 and 1, to be understood by Computers. For
Example, An IPv4 Address can be written as 189.123.123.90.
An IPv6 address type is designed of 128 bits from which 4 are hexadecimal digits, and it created eight sets, with each
block containing 16 bits separated by a colon (:).
Subnetting : It is the practice of dividing a single, large network into smaller sub-networks or subnets.
Why Subnet?
Optimized Addressing: Better use of IP address space
Isolation: Segmenting parts of the network for security and traffic management
Hierarchical Design: Simplifies network design and troubleshooting
Efficient Routing: Reduces broadcast traffic and improves routing efficiency
We always reserve an IP address to identify the subnet and another one to identify the broadcast address
within the subnet.

4. A subnet mask is a 32- or 128-bit number that segments an existing IP address in a TCP/IP network. It is used by the
TCP/IP protocol to determine whether a host is on the local subnet or on a remote network. Subnet mask divides the IP
address into a network address and host address, hence to identify which part of IP address is reserved for the network
and which part is available for host use. Once given the IP address and its subnet mask, the network address (subnet) of
a host can be determined.
Subnet Mask :
In TCP/IP configuration, we cannot determine whether a part of the IP address is used as network or host address unless
we get more information from a subnet mask table. If the subnet mask example is 255.255.255.0, and since 255 in binary
notation equals 11111111, so the subnet mask is:
11111111.11111111.11111111.0000000.
Lining up the IP address and the subnet mask together, the network and host portions of the address can be separated:
11000000.10101000.01111011.10000100 -- IP address (192.168.123.132)
11111111.11111111.11111111.00000000 -- Subnet mask (255.255.255.0)
The first 24 bits are identified as the network address, with the last 8 bits (the remaining zeros in the subnet mask)
identified as the host address. This gives you the following:
11000000.10101000.01111011.00000000 -- Network address (192.168.123.0)
00000000.00000000.00000000.10000100 -- Host address (000.000.000.132)

5. Classes of IP Addresses
The five classes of IP addresses are A, B, C, D, and E, and are defined by the first four bits of an IP address's first octet.
The classes are characterized by the number of networks available and the number of hosts available on each network.
The first three classes (A, B, and C) can be used for host addresses, and are primarily used by the majority of devices on
the internet. Classes D and E are for special uses.
Class A :
Starts with 0
First Octet: Ranges from 1 to 126
Subnet Mask: 255.0.0.0
Possible Host: 16,777,214 (2^24 - 2)
Class A addresses are less commonly used for individual organizations or home networks due to their large size and the
limited number of Class A address blocks available. They are more commonly assigned to ISPs or large organizations
that require a large number of IP addresses.
An IP address that starts with a value between 0 and 127 in the first octet is a Class A address. The first octet of a Class A
address always begins with a zero. The numbers 0 and 127 are reserved and cannot be used as a network address.
Number of usable hosts in any network can be calculated with the formula = 2x– 2, where x is the
number of host ID bits in the IP address.

6. Class B :
A Class B address consists of a 16-bit network address and a 16-bit local or host address. The first two bits in the network
address are dedicated to indicating the network class, leaving 14 bits for the actual network address.
Range: 128.0.0.0 to 191.255.255.255
First Octet: Ranges from 128 to 191
Subnet Mask: 255.255.0.0
Possible Network Addresses : 16,384
Possible Local Host Addresses: 65,534 (2^16 - 2)
Class B IP addresses strike a balance between the large scope of Class A and the smaller, more manageable size of
Class C. They are versatile and can be suitable for both public-facing networks and large private networks.
Class C :
The first three bits of the first octet are always 110, and the remaining 21 bits complete the network ID. The last octet
(8 bits) represents the host ID. For example, 192.5.2.5 is a typical class C address where 192.5.2 is the network number
and 5 is the host number.
Usage: Home Networks, Small Businesses, Branch Offices

7. Range: 192.0.0.0 to 223.255.255.255
First Octet: Ranges from 192 to 223
Subnet Mask: 255.255.255.0
Network addresses : 20971520(2^21-2)
Total Host Addresses: 254 (2^8 - 2)
Class D :
Class D IP addresses are used for multicast addressing in IPv4. Multicasting allows a host to send a single packet to
multiple recipients. Unlike unicast addresses (which are used for one-to-one communication) and broadcast addresses
(which are used for one-to-all communication within a local network), multicast addresses allow one-to-many
communication. Class D addresses are specifically reserved for this purpose.
Class D IP addresses have the first four bits of the first octet set to 1110, and the remaining bits determine the host
address. The IP address range for Class D is 224.0.0.0 to 239.255.255.255.
Range: 224.0.0.0 to 239.255.255.255
First Octet: Ranges from 224 to 239
Subnet Mask: Typically 240.0.0.0 or /4 in CIDR notation
Class D does not possess any subnet mask.

8. Class E :
This class is reserved for future use, research and development purposes. It also doesn't have any subnet mask.
First Octet: Ranges from 240 to 255
Subnet Mask: 255.255.255.255 (Used to specify a single host)
Total Number of Addresses: 268,435,456 (2^28)
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