IPv4 supports three different types of addressing modes. −
Unicast Addressing Mode
In this mode, data is sent only to one destined host. The Destination Address field contains 32- bit IP address of the destination host. Here the client sends data to the targeted server −
Broadcast Addressing Mode
In this mode, the packet is addressed to all the hosts in a network segment. The Destination Address field contains a special broadcast address, i.e. 255.255.255.255. When a host sees this packet on the network, it is bound to process it. Here the client sends a packet, which is entertained by all the Servers −
Multicast Addressing Mode
This mode is a mix of the previous two modes, i.e. the packet sent is neither destined to a single host nor all the hosts on the segment. In this packet, the Destination Address contains a special address which starts with 224.x.x.x and can be entertained by more than one host.
IPv4 subnet masks
All IP addresses are divided into portions. One part identifies the network (the network number) and the other part identifies the specific machine or host within the network (the host number). Subnet masks (IPv4) identify the range of IP addresses that make up a subnet, or group of IP addresses on the same network. For example, a subnet can be used to identify all the machines in a building, department, geographic location, or on the same local area network (LAN).
Dividing an organization's network into subnets allows it to be connected to the Internet with a single shared network address. Subnet masks and prefixes are used when a host is attempting to communicate with another system. If the system is on the same network or subnet, it attempts to find that address on the local link. If the system is on a different network, the packet is sent to a gateway that then routes the packet to the correct IP address. This routing is called Classless-InterDomain Routing (CIDR).
In IPv4, the subnet mask 255.255.255.0 is 32 bits and consists of four 8-bit octets.
What is Classful Addressing?
Classful addressing is a network addressing the Internet’s architecture from 1981 till Classless Inter-Domain Routing was introduced in 1993.
This addressing method divides the IP address into five separate classes based on four address bits.
Here, classes A, B, C offers addresses for networks of three distinct network sizes. Class D is only used for multicast, and class E reserved exclusively for experimental purposes.
Class A - Over 16 million host identifiers
Class B - 65,535 host identifiers
Class C - 254 host identifiers
Let’s see each of the network classes in detail:
Class A Network
This IP address class is used when there are a large number of hosts. In a Class A type of network, the first 8 bits (also called the first octet) identify the network, and the remaining have 24 bits for the host into that network.
An example of a Class A address is 102.168.212.226. Here, “102” helps you identify the network and 168.212.226 identify the host.
Class A addresses 127.0.0.0 to 127.255.255.255 cannot be used and is reserved for loopback and diagnostic functions.
Class B Network
In a B class IP address, the binary addresses start with 10. In this IP address, the class decimal number that can be between 128 to 191. The number 127 is reserved for loopback, which is used for internal testing on the local machine. The first 16 bits (known as two octets) help you identify the network. The other remaining 16 bits indicate the host within the network.
An example of Class B IP address is 168.212.226.204, where 168 212 identifies the network and 226.204 helps you identify the Hut network host.
Class C Network
Class C is a type of IP address that is used for the small network. In this class, three octets are used to indent the network. This IP ranges between 192 to 223.
In this type of network addressing method, the first two bits are set to be 1, and the third bit is set to 0, which makes the first 24 bits of the address them and the remaining bit as the host address. Mostly local area network used Class C IP address to connect with the network.
Example for a Class C IP address:
192.168.178.1
Class D Network
Class D addresses are only used for multicasting applications. Class D is never used for regular networking operations. This class addresses the first three bits set to “1” and their fourth bit set to use for “0”. Class D addresses are 32-bit network addresses. All the values within the range are used to identify multicast groups uniquely.
Therefore, there is no requirement to extract the host address from the IP address, so Class D does not have any subnet mask.
Example for a Class D IP address:
227.21.6.173
Class E Network
Class E IP address is defined by including the starting four network address bits as 1, which allows you two to incorporate addresses from 240.0.0.0 to 255.255.255.255. However, E class is reserved, and its usage is never defined. Therefore, many network implementations discard these addresses as undefined or illegal.
Example for a Class E IP address:
243.164.89.28
Source- guru99