Question 361 of 2,152

EIGRP Troubleshooting →hardMultiple ChoiceObjective-mapped

EIGRP Route Flapping: Summary Route Metric Inconsistency

This 300-410 practice question tests your understanding of eigrp troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 network engineer is troubleshooting an EIGRP issue where a route is flapping in and out of the routing table. The engineer checks the logs and sees messages indicating that the route is being learned from two different neighbors, but the metric keeps changing. The route is a summary route. What is the most likely cause of the flapping?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The summary route is being advertised by multiple routers with different metrics.
Correct because if the summary route is originated by multiple routers, the metric may vary, causing the router to flap between the best paths.
B
The EIGRP stub feature is configured on one of the neighbors.
Why wrong: Incorrect because stub routing prevents the router from being a transit router, but it does not cause route flapping due to metric changes.
C
The passive-interface command is applied to the interface receiving the summary route.
Why wrong: Incorrect because passive-interface would prevent the router from sending hellos, not cause flapping of a learned route.
D
The EIGRP router ID is the same on both neighbors.
Why wrong: Incorrect because duplicate router IDs can cause route instability, but they would not cause a summary route to flap specifically due to metric changes.

Full breakdown with real-world context →

Quick Answer

The answer is that the summary route is being advertised by multiple routers with different metrics, causing EIGRP route flapping. This occurs because when a summary route is learned from two different neighbors, the router compares the metrics and selects the best path; if the metrics are inconsistent, the router constantly switches between the two advertisements, removing and reinserting the route from the routing table. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of EIGRP summarization behavior and metric consistency, often appearing as a troubleshooting question where logs show fluctuating metrics for a summary route. A common trap is to blame a mismatched K-value or a redistribution issue, but the core problem is that multiple routers originate the same summary with differing composite metrics. Memory tip: “Multiple metrics, multiple neighbors—flapping follows.”

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The summary route is being advertised by multiple routers with different metrics.

When a summary route is learned from multiple EIGRP neighbors with different metrics, the router will alternate between the best paths as the metrics change, causing the route to flap in and out of the routing table. EIGRP uses the feasible successor logic, but if the metric from each neighbor varies (e.g., due to unequal link speeds or load), the route may be repeatedly inserted and withdrawn as the topology table updates.

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 route is being advertised by multiple routers with different metrics.
Why this is correct
Correct because if the summary route is originated by multiple routers, the metric may vary, causing the router to flap between the best paths.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The EIGRP stub feature is configured on one of the neighbors.
Why it's wrong here
Incorrect because stub routing prevents the router from being a transit router, but it does not cause route flapping due to metric changes.
✗
The passive-interface command is applied to the interface receiving the summary route.
Why it's wrong here
Incorrect because passive-interface would prevent the router from sending hellos, not cause flapping of a learned route.
✗
The EIGRP router ID is the same on both neighbors.
Why it's wrong here
Incorrect because duplicate router IDs can cause route instability, but they would not cause a summary route to flap specifically due to metric changes.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume flapping is caused by neighbor adjacency issues (like duplicate router IDs) or interface misconfigurations, rather than recognizing that metric instability between multiple sources of the same summary route is the root cause.

Detailed technical explanation

How to think about this question

EIGRP uses the Diffusing Update Algorithm (DUAL) to maintain loop-free paths. When a summary route is advertised by multiple neighbors, the router computes the composite metric (bandwidth, delay, reliability, load, MTU) for each path. If the metrics differ and fluctuate (e.g., due to interface counters or load changes), the route may alternate between feasible successor and successor states, causing the flapping. This is often seen in redistribution scenarios or when summary routes are manually configured with varying costs.

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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

Quick reference

Routing Protocol Comparison

Protocol	Metric	Max Hops	Algorithm	Type
RIP v2	Hop count	15	Bellman-Ford	Distance vector
OSPF	Cost (bandwidth)	Unlimited	Dijkstra (SPF)	Link state
EIGRP	Composite metric	Unlimited	DUAL	Hybrid
IS-IS	Cost	Unlimited	Dijkstra	Link state
BGP	Policy / attributes	Unlimited	Path vector	Path vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Related 300-410 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Layer 3 Technologies practice questions

Practise 300-410 questions linked to Layer 3 Technologies.

EIGRP Troubleshooting practice questions

Practise 300-410 questions linked to EIGRP Troubleshooting.

OSPF Troubleshooting (v2/v3) practice questions

Practise 300-410 questions linked to OSPF Troubleshooting (v2/v3).

BGP Troubleshooting practice questions

Practise 300-410 questions linked to BGP Troubleshooting.

Route Redistribution practice questions

Practise 300-410 questions linked to Route Redistribution.

Policy-Based Routing (PBR) practice questions

Practise 300-410 questions linked to Policy-Based Routing (PBR).

VRF-Lite practice questions

Practise 300-410 questions linked to VRF-Lite.

Route Maps and Route Filtering practice questions

Practise 300-410 questions linked to Route Maps and Route Filtering.

Administrative Distance practice questions

Practise 300-410 questions linked to Administrative Distance.

Route Summarization practice questions

Practise 300-410 questions linked to Route Summarization.

Bidirectional Forwarding Detection (BFD) practice questions

Practise 300-410 questions linked to Bidirectional Forwarding Detection (BFD).

VPN Technologies practice questions

Practise 300-410 questions linked to VPN Technologies.

Practice this exam

Start a free 300-410 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

300-410 practice-test guide →Study guide →Browse all practice tests

FAQ

Questions learners often ask

What does this 300-410 question test?

EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The summary route is being advertised by multiple routers with different metrics. — When a summary route is learned from multiple EIGRP neighbors with different metrics, the router will alternate between the best paths as the metrics change, causing the route to flap in and out of the routing table. EIGRP uses the feasible successor logic, but if the metric from each neighbor varies (e.g., due to unequal link speeds or load), the route may be repeatedly inserted and withdrawn as the topology table updates.

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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Keep practising

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.