Classful Addressing in IP Addressing

Benchmark	Physical Address	Logical Address
Representation	Represents the actual physical location of data in memory or devices	A virtual or symbolic representation of memory locations, used by software programs
Generation	Generated based on the hardware architecture and memory configuration	Generated by the CPU while a program is running
Address Translation	Used directly by hardware to access memory locations, no translation required	Must be translated or mapped to its corresponding physical address by the Memory Management Unit (MMU) before being used by hardware
Address Space	Limited by the amount of installed physical memory in the system	Can be part of a larger virtual address space, exceeding the available physical memory
Portability	Tied to a specific hardware architecture and memory layout, not portable across systems	More portable across different systems and architectures, as long as the address translation mechanisms are compatible
Purpose	Directly accessed by hardware components for low-level operations and efficient data transfer	Used by software programs and operating systems for memory management, memory protection, and efficient resource sharing
Abstraction Level	Low-level, hardware-specific addresses	Higher-level, software-friendly addresses
Mapping	No mapping required, directly used by hardware	Mapped or translated to physical addresses by the MMU
Memory Access	Provides direct access to physical memory locations	Provides an abstraction layer over physical memory access
Memory Management Features	Limited memory management features	Enables features like virtual memory, demand paging, swapping, and shared memory

• An IP address is a number that contains information about a host's location, particularly when it's not within a local area network. An IP address is a unique 32-bit address with 232 address space.
• Hexadecimal notation and dotted decimal notation are the two common notations used to write IP addresses.

Dotted Decimal Notation

Hexadecimal Notation

Observations regarding dotted decimal notation 

1. Any segment's (byte's) value falls between 0 and 255 (both included).
2. In every segment, the value comes before any zeros (054 is incorrect, 54 is correct).

Classful Addressing

• The 32-bit IP address is divided into five sub-classes. These are: 

• Class A
• Class B
• Class C
• Class D
• Class E
• There is a suitable range of IP addresses for each of these classes. For multicast and experimental reasons, respectively, classes D and E are set aside. 
• The IP address's classes are determined by the bits in the first octet. 
• The IPv4 address is divided into two parts:

1. Network ID
2. Host ID

• The bits used for network ID and host ID, as well as the total number of networks and hosts that can be included in that specific class, are determined by the class of IP address. 
• Every device connected to a network is given an IP address by the network administrator or ISP. 

Note:-

1. Regional Internet registries (RIR) and the Internet Assigned Numbers Authority (IANA) oversee IP addresses internationally.
2. Since the last IP address is allocated for broadcast IP and the first IP address of any network is the network number, two IP addresses are not counted when determining the total number of host IP addresses. As a result, the total count is dropped.

Class A

• Large numbers of hosts are found on networks that are assigned class A IP addresses. 

• The network ID consists of 8 bits.
• The host ID consists of 24 bits.
• In class A, the first octet's higher-order bit is always set to 0. 
• The network ID is determined by the final 7 bits of the first octet. 
• Any network's host can be identified using the 24 bits of the host ID. 
• For Class A, the default subnet mask is 255.x.x.x. As a result, class A's total is:

• Class A host ID IP addresses range from 1.0.0.0 to 126.255.255.255.
•  2^24 – 2 = 16,777,214. 

Class B

• Networks ranging in size from medium-sized to large-sized are issued IP addresses under class B. 

• The network ID consists of 16 bits.
• The host ID consists of 16 bits.
• Class B IP addresses always have their first octet's higher-order bits set to 10. 
• The network ID is found using the final 14 bits. 
• Any network's host can be identified using the 16 bits of the host ID. Class B's default subnet mask is 255.255.x.x. 

• For Class B, the total is: 2^14 = 16384 network address 2^16 – 2 = 65534 host address 
• Class B IP addresses start at 128.0.0.0 and go up to 191.255.255.255.

Class C

• Class C IP addresses are given to networks with less than ten users.

• The network ID consists of 24 bits.
• The host ID consists of 8 bits.
• IP addresses belonging to class C always have their first octet's higher-order bits set to 110. The network ID is found using the final 21 bits. 
• Any network's host can be identified using the eight bits of the host ID. 

• Class C's default subnet mask is 255.255.255.x. 
• In total, Class C possesses: 2^21=2097152 network address.
• IP addresses that belong to class C range from 192.0.0.0 to 223.255.255.255.
• 2^8 – 2 = 254 host addresses.

Class D

• Class D IP addresses are set aside for multicasting. Class D IP addresses always have their first octet's higher-order bits set to 1110. 
• The addresses that interested hosts recognize are represented by the remaining bits.
• There is no subnet mask in Class D. 
• Class D IP addresses fall between 224.0.0.0 to 239.255.255.255.

Class E

• Class E IP addresses are set aside for use in experimentation and research. 
• The range of class E IP addresses is 240.0.0.0 to 255.255.255.254. 
• There isn't a subnet mask for this class. Class E's first octet's higher-order bits are always set to 1111.

Different Classes

Rules for Assigning Host ID

1. Within a network, hosts are identified by their host IDs. The following guidelines are used to assign the host ID:
2. Any network requires the host ID to be exclusive to that network.
3. Since this host ID is used to indicate the network ID of the IP address, it is not possible to assign a host ID with all bits set to 0.
4. It is not possible to provide a host ID with all bits set to 1, as it is designated as a broadcast address for sending packets to every host on that specific network.

Classless Addressing

• The subnetting and supernetting strategies used in classfull addressing did not completely solve the address depletion problem. 
• As the Internet grew, it became clear that a larger address space was needed as a permanent solution. But larger IP addresses are also required due to the enlarged address space, which means that IP packet syntax must be altered. 
• Although the long-term solution, known as IPv6, has already been devised, the short-term solution was still produced, using the same address space but changing the allocation of addresses to provide a fair amount to each organization. 
• The workaround, which uses IPv4 addresses still, is classless addressing. The class privilege was removed from the distribution to compensate for address depletion.
• Classless addressing divides the entire address space into chunks of different sizes. The prefix of an address identifies the block (network); the suffix identifies the node (device).
• We are capable of having a block of 20, 21, 22 ,..., 232 addresses, theoretically. The requirement that a block of addresses have a power of two addresses is one of the restrictions. 
• An organization may be assigned one address block. The entire address space is segmented into non-overlapping blocks, as seen in the provided figure.

Classless

• Classless addressing permits different prefix lengths than classfull addressing. It is conceivable for prefix lengths to range from 0 to 32. 
• The prefix's length and network size are inversely correlated. The prefix of a larger network is little, and the prefix of a smaller network is large.
• It is important to emphasize that the idea of classless addressing can be applied to classfull addressing with equal ease. Think of a class A address as a classless address with an 8-character prefix length. 
• Class B addresses with the prefix 16 and higher can be considered classless addresses. Stated differently, classless addressing is a particular kind of classfull addressing.

Difference Between Classful and Classless Addressing

• IP addresses are divided into five groups using the classfull addressing approach when they are assigned. In order to prevent the depletion of IP addresses, classless addressing is used. It is a method of IP address allocation that will eventually replace classfull addressing.
• A further distinction is the usefulness of classfull and classless addressing. Comparatively speaking, classless addressing is more beneficial and useful than classfull addressing.
• In classfull addressing, the network ID and host ID are adjusted according to the classes. However, the distinction between network ID and host ID does not exist with classless addressing. This opens up the possibility of making yet another contrast between both addressing.