The correct answer is B. In classless addressing, the first address assigned to an organization must be evenly divisible by the number of addresses required. This concept is fundamental to understanding how IP addressing works in classless addressing schemes, such as CIDR (Classless Inter-Domain Routing).

Let’s explore in detail why this answer is correct and why the other options are not accurate descriptions of the requirements for the first address in classless addressing.

B. Must Be Evenly Divisible by the Number of Addresses (Correct Answer):

In classless addressing, IP addresses are allocated in a flexible manner, and address blocks are created based on the actual number of addresses needed by an organization.

The first address in such a block is determined in a way that ensures efficient allocation and use of IP addresses. It is important for this first address to be evenly divisible by the number of addresses required for several reasons:

1. Efficient Use of Address Space:

To maximize the efficient utilization of IP address space, it is essential to allocate address blocks that precisely match the organization’s requirements. By making the first address evenly divisible by the number of addresses needed, there is no wasted space, and the organization can use all the addresses in the block.

2. Address Alignment:

Divisibility ensures that the starting point of the address block aligns with the appropriate boundaries and subnets. This simplifies network management and routing, as addresses are organized neatly and predictably.

3. Simplicity in Allocation:

Address blocks with the first address evenly divisible by the number of addresses required are easier to manage and allocate. It eliminates the need for additional adjustments and calculations when assigning addresses to different subnets or devices.

Now, let’s discuss why the other options are not correct:

A. Must Be a Power of 4:

Requiring the first address to be a power of 4 is not a characteristic of classless addressing. Classless addressing allows for a flexible allocation of IP addresses based on the actual needs of an organization, and the first address does not need to be a power of 4. It should align with the specific requirements of the organization in terms of the number of addresses.

C. Must Belong to One of the A, B, or C Classes:

Classless addressing, as the name suggests, does not adhere to the traditional classes (A, B, or C) of IP addressing. Instead, it uses variable-length subnet masks and allows for more efficient allocation of IP addresses.

In classless addressing, the allocation is not based on predefined classes, and the first address is determined based on the number of addresses needed, not class boundaries.

D. None of the Above:

This option is not correct because, as explained, the first address in classless addressing schemes is required to be evenly divisible by the number of addresses required. This is a fundamental principle of efficient IP address allocation in classless addressing and is not accurately described as “none of the above.”

In summary, the first address assigned to an organization in classless addressing must be evenly divisible by the number of addresses needed.

This practice is essential for efficient IP address allocation, alignment with network boundaries, and simplifying network management. The other options do not accurately represent the requirements and characteristics of classless addressing in IP networking.