The answer is the summary address on R2 causing query suppression for the specific route. When R2 is configured with ip summary-address eigrp 100 10.0.0.0 255.255.255.0, it advertises only the aggregate 10.0.0.0/24 to R1, suppressing replies to queries for more specific prefixes within that range. As a result, when R1 loses its route to 10.0.0.0/24 and sends a query for that exact prefix, R2 never responds because the summary address blocks the query, leaving R1 stuck-in-active (SIA) waiting indefinitely. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of EIGRP query scoping and the SIA mechanism—a common trap is confusing summary address suppression with a simple missing route. Remember: a summary address acts like a query black hole for its covered subnets. Memory tip: “Summary suppresses, SIA stresses.”
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.
EIGRP network is experiencing stuck-in-active (SIA) routes. Router R1 shows: show ip eigrp topology active includes 10.0.0.0/24. Router R2 has: interface GigabitEthernet0/0, ip summary-address eigrp 100 10.0.0.0 255.255.255.0. 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 summary address on R2 is causing a query for the specific route to be suppressed.
The correct answer is A because the summary address configured on R2 (ip summary-address eigrp 100 10.0.0.0 255.255.255.0) causes R2 to advertise a single summary route (10.0.0.0/24) to R1. When R1 loses its route to 10.0.0.0/24 and sends a query for the specific prefix, R2 does not reply because the summary address suppresses the query for the more specific route, leaving R1 stuck-in-active (SIA) waiting for a reply that never comes.
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 on R2 is causing a query for the specific route to be suppressed.
Why this is correct
Summary addresses can cause queries to be aggregated, leading to SIA if replies are not received.
Related concept
Read the scenario before looking for a memorised answer.
✗
R1 has a stuck interface causing the SIA.
Why it's wrong here
SIA is due to query/reply issues, not interface state.
✗
EIGRP is misconfigured with wrong autonomous system number.
Why it's wrong here
AS number mismatch would prevent neighbor formation.
✗
The route 10.0.0.0/24 is flapping, causing continuous queries.
Why it's wrong here
Flapping can cause SIA, but the summary is the direct cause here.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the subtle interaction between EIGRP summary addresses and query suppression, where candidates mistakenly think SIA is caused by flapping or interface issues, rather than understanding that a summary address on a downstream router can prevent query replies for more specific prefixes.
Detailed technical explanation
How to think about this question
EIGRP uses a Diffusing Update Algorithm (DUAL) to maintain loop-free paths. When a successor route is lost, the router sends queries to all neighbors; if a neighbor has a summary route covering the queried prefix, it does not reply because the summary is considered a local route that does not require a query response. This behavior is defined in RFC 7868, where summary addresses are treated as local entries that suppress queries for more specific prefixes, potentially causing SIA if the querying router does not receive a reply within the active timer (default 3 minutes).
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 summary address on R2 is causing a query for the specific route to be suppressed. — The correct answer is A because the summary address configured on R2 (ip summary-address eigrp 100 10.0.0.0 255.255.255.0) causes R2 to advertise a single summary route (10.0.0.0/24) to R1. When R1 loses its route to 10.0.0.0/24 and sends a query for the specific prefix, R2 does not reply because the summary address suppresses the query for the more specific route, leaving R1 stuck-in-active (SIA) waiting for a reply that never comes.
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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