300-320 · Question #207
There are 3 steps to confirm whether a range of IP addresses can be summarized. Which of the following is used in each of these 3 steps?
The correct answer is C. The size of the contiguous block of addresses. The block size is the single value used across all three steps of validating whether a range of IP addresses can be summarized into a single prefix.
Question
There are 3 steps to confirm whether a range of IP addresses can be summarized. Which of the following is used in each of these 3 steps?
Options
- AThe first number in the contiguous block of addresses
- BThe last number in the contiguous block of addresses
- CThe size of the contiguous block of addresses
- DThe subnet mask of the original network address
How the community answered
(39 responses)- A3% (1)
- C95% (37)
- D3% (1)
Why each option
The block size is the single value used across all three steps of validating whether a range of IP addresses can be summarized into a single prefix.
The first address is used in step 2 to test divisibility by the block size, but it is not independently required in all three steps.
The last address is derived from the first address plus the block size minus one; it is not a standalone input used across all three verification steps.
The three summarization validation steps are: (1) verify the block size is a power of 2, (2) verify the first address of the block is evenly divisible by the block size, and (3) verify all addresses in the range fit within the resulting summary prefix - the block size is the central value required in every one of these three checks.
The subnet mask of the original network is an output of the summarization process derived from the block size, not a value used as input in each of the three steps.
Concept tested: IP route summarization block size validation
Source: https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/13701-16.html
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