Lec-47: What is Classless Addressing (CIDR) in Hindi | CIDR vs Classful Addressing

Summary

This video explains the concept of Classless Addressing (CIDR), introduced in 1993 as a more flexible alternative to Classful Addressing. Unlike Classful Addressing, which divides IP addresses into fixed classes, Classless Addressing provides IP address blocks based on user demand, reducing wastage. The video covers the importance of block sizes, the use of the /n notation, and how to calculate network and host IDs. It also emphasizes CIDR's rules, such as the need for contiguous addresses and powers of 2, making it crucial for efficient IP address allocation.

Takeaways

• 😀 Classless Addressing (CIDR) was introduced in 1993 as a solution to the limitations of Classful Addressing.
• 😀 In Classful Addressing, IP addresses are assigned in fixed classes (A, B, C, etc.), leading to wastage of IP addresses.
• 😀 Classless Addressing allows for flexible allocation of IP address blocks based on the exact number of addresses a user needs.
• 😀 In CIDR, IP addresses are grouped in blocks, and the concept of classes (A, B, C) no longer applies.
• 😀 CIDR notation includes the IP address followed by a slash and a number (e.g., 200.10.20.40/28), where the number indicates the number of bits used for the network.
• 😀 The network portion of the IP address is determined by the number following the slash in CIDR notation (e.g., /28).
• 😀 CIDR notation improves flexibility by reducing wastage of IP addresses, providing users only the number of addresses they require.
• 😀 The subnet mask in CIDR defines how many bits are dedicated to the network portion of the IP address, allowing for more efficient use of IP space.
• 😀 To calculate the number of hosts in a network, subtract the network bits from the total number of bits (32 for IPv4). For example, /28 leaves 4 bits for hosts, allowing for 16 hosts.
• 😀 CIDR follows three key rules: IP addresses should be contiguous, the number of addresses must be a power of 2, and the first address must be divisible by the size of the block.

Q & A

What is Classless Addressing (CIDR), and when was it introduced?

Classless Addressing (CIDR) is a method of IP address allocation that replaced the rigid Classful Addressing system. It was introduced in 1993 to provide more flexibility in allocating IP addresses, particularly by allowing IP address blocks of varying sizes based on user needs.

What are the main drawbacks of Classful Addressing?

Classful Addressing was inflexible because it allocated fixed-sized blocks of IP addresses (Class A, B, C, etc.), leading to inefficient use of IP addresses. For instance, if a user needed 1,000 IPs but only had access to a Class A address, they would end up wasting millions of IP addresses.

How does Classless Addressing differ from Classful Addressing?

In Classless Addressing, IP addresses are allocated in blocks based on the user's specific needs, rather than being assigned according to a predefined class (A, B, C). This allows for a more efficient use of IP addresses, minimizing wastage compared to Classful Addressing.

What is meant by 'blocks' in Classless Addressing?

In Classless Addressing, a 'block' refers to a group of IP addresses allocated to a user. The size of the block is determined by the user's demand, meaning the block size is flexible and can be adjusted as needed, unlike the fixed classes in Classful Addressing.

What does the notation 'x.y.z.w/n' represent in Classless Addressing?

'x.y.z.w' represents the IP address, while '/n' represents the subnet mask. The number 'n' indicates how many bits in the IP address are used for the network (Block ID) portion. This helps determine the network size and the number of host addresses available.

How do you calculate the number of hosts in a network using CIDR notation?

The number of hosts is calculated by subtracting the number of network bits (represented by 'n' in CIDR notation) from 32 (the total number of bits in an IPv4 address). The result is then used to calculate the number of hosts using the formula 2^x, where x is the number of host bits.

What is the importance of the '/n' notation in CIDR?

The '/n' notation is crucial because it helps identify the network portion of the IP address. The 'n' represents the number of bits used for the network ID (Block ID). This allows for dynamic and precise allocation of IP addresses, ensuring minimal wastage and efficient network segmentation.

Can you explain the process of finding the Network ID using CIDR notation?

To find the Network ID using CIDR notation, you perform a bitwise AND operation between the IP address and the subnet mask (derived from the '/n' notation). This operation gives you the network address by zeroing out the host bits in the IP address.

What are the three main rules for Classless Addressing (CIDR)?

The three main rules for CIDR are: 1) Addresses in a block should be contiguous, meaning they must follow one after another without gaps. 2) The number of addresses in a block must be a power of 2. 3) The first address in a block must be divisible by the block's size, ensuring it aligns correctly with the block's structure.

Why is the rule that the first address of a block must be divisible by the block size important?

This rule ensures that the network's address is properly aligned with the block size. For example, if the block size is 16, the first address must end in four zero bits (in binary) to ensure correct network addressing. This prevents misalignment and ensures valid IP address assignments.