The answer is that the EIGRP summary address suppresses more specific routes within its range, which is exactly why R2 sees the 10.0.0.0/22 summary but not the 10.0.3.0/24 route. When you configure the `ip summary-address eigrp` command on an interface, EIGRP automatically creates a single summary route and stops advertising any component routes that fall within that summary prefix, a behavior known as route suppression. This is a core concept tested on the Cisco CCNP ENARSI 300-410 exam, where you must understand that summarization reduces routing table size and update overhead by replacing multiple specific routes with one aggregate. A common trap is assuming the more specific routes are still sent alongside the summary; in reality, EIGRP suppresses them by default unless you explicitly configure a leak-map. Remember the memory tip: "Summary means suppress—the specific routes take a rest."
300-410 IPv4 Access Control Lists Practice Question
This 300-410 practice question tests your understanding of ipv4 access control lists. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A large enterprise network uses EIGRP with route summarization. Router R1 has the following configuration: interface GigabitEthernet0/0, ip summary-address eigrp 100 10.0.0.0 255.255.252.0. Router R2 shows: show ip route eigrp includes 10.0.0.0/22 but not 10.0.3.0/24. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The EIGRP summary address suppresses more specific routes within its range.
Option C is correct because the EIGRP `ip summary-address` command on R1 creates a summary route (10.0.0.0/22) that is advertised to R2, and by default EIGRP suppresses the advertisement of all more specific routes that fall within the summary range (10.0.0.0/22 includes 10.0.3.0/24). This is the intended behavior of EIGRP route summarization: the summary route replaces the component routes to reduce routing table size and update overhead.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The summary address is misconfigured; it should be 10.0.0.0/24.
Why it's wrong here
The summary is correct for the range; the issue is suppression of specifics.
✗
R2 has a route filter blocking 10.0.3.0/24.
Why it's wrong here
No evidence of a filter; the summary suppresses the specific route.
✓
The EIGRP summary address suppresses more specific routes within its range.
Why this is correct
EIGRP summary addresses automatically suppress more specific routes, causing the missing /24.
Related concept
Read the scenario before looking for a memorised answer.
✗
R1's interface is down, preventing route advertisement.
Why it's wrong here
The summary is present, so the interface is up.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that EIGRP summarization simply advertises a summary route in addition to the more specific routes, when in fact the default behavior is to suppress all component routes within the summary range.
Detailed technical explanation
How to think about this question
EIGRP's `ip summary-address` command creates a local summary route on the interface and automatically installs a discard route (null0) for the summary prefix to prevent routing loops. The suppression of more specific routes is a fundamental design choice to reduce the size of EIGRP updates and query scopes; this behavior is controlled by the `summary-metric` and `leak-map` options, but by default all component routes are suppressed. In real-world scenarios, this can cause reachability issues if a more specific route is needed for traffic engineering or if the summary range is too broad.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The EIGRP summary address suppresses more specific routes within its range. — Option C is correct because the EIGRP `ip summary-address` command on R1 creates a summary route (10.0.0.0/22) that is advertised to R2, and by default EIGRP suppresses the advertisement of all more specific routes that fall within the summary range (10.0.0.0/22 includes 10.0.3.0/24). This is the intended behavior of EIGRP route summarization: the summary route replaces the component routes to reduce routing table size and update overhead.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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