Question 1,276 of 2,152

BGP Troubleshooting →hardMultiple ChoiceObjective-mapped

Route Reflector Cluster ID Misconfiguration

This 300-410 practice question tests your understanding of bgp troubleshooting. 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.

An engineer configures a route reflector cluster with two route reflectors in the same cluster ID. After convergence, some iBGP routes are missing on clients, and 'show ip bgp' shows the path with 'r' flag. What is the most likely explanation?

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 cluster ID is misconfigured and should be unique per route reflector.
Route reflectors with the same cluster ID will reject routes from each other to prevent loops, leading to missing routes on clients.
B
The route reflectors have different BGP AS numbers, causing the 'r' flag to indicate a routing loop.
Why wrong: Different AS numbers would not cause the 'r' flag; that flag indicates the route was received from a route reflector in the same cluster.
C
The clients have 'no bgp default route-reflector-client' configured, preventing them from receiving reflected routes.
Why wrong: This command is not valid; clients are defined under the neighbor statement with 'route-reflector-client'.
D
The route reflectors have 'bgp cluster-id' set to 0.0.0.0, which disables cluster-based loop prevention.
Why wrong: Setting cluster-id to 0.0.0.0 is not allowed; the default cluster ID is the router ID.

Full breakdown with real-world context →

Quick Answer

The answer is a misconfigured cluster ID that should be unique per route reflector. When two route reflectors share the same cluster ID, they treat each other’s updates as originating from the same cluster, triggering the route reflector loop prevention mechanism. This mechanism drops routes learned from another RR within the same cluster, causing missing iBGP routes on clients that are not fully meshed, as the 'r' flag in 'show ip bgp' indicates a received but rejected route due to cluster-list checking. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of BGP route reflection and loop prevention, often appearing as a trap where you might assume redundancy requires identical cluster IDs. A common memory tip is to think of the cluster ID as a unique “team jersey”—if two players wear the same number, the referee (loop prevention) will ignore one player’s pass, breaking the play.

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 cluster ID is misconfigured and should be unique per route reflector.

When two route reflectors share the same cluster ID, they treat each other's updates as if from the same cluster. The route reflector loop prevention mechanism drops routes learned from another RR in the same cluster, causing route loss if the clients are not fully meshed.

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 cluster ID is misconfigured and should be unique per route reflector.
Why this is correct
Route reflectors with the same cluster ID will reject routes from each other to prevent loops, leading to missing routes on clients.
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 route reflectors have different BGP AS numbers, causing the 'r' flag to indicate a routing loop.
Why it's wrong here
Different AS numbers would not cause the 'r' flag; that flag indicates the route was received from a route reflector in the same cluster.
✗
The clients have 'no bgp default route-reflector-client' configured, preventing them from receiving reflected routes.
Why it's wrong here
This command is not valid; clients are defined under the neighbor statement with 'route-reflector-client'.
✗
The route reflectors have 'bgp cluster-id' set to 0.0.0.0, which disables cluster-based loop prevention.
Why it's wrong here
Setting cluster-id to 0.0.0.0 is not allowed; the default cluster ID is the router ID.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Trap categories for this question

Command / output trap
This command is not valid; clients are defined under the neighbor statement with 'route-reflector-client'.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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.

What to study next

Got this wrong? Here's your next step.

Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this 300-410 question test?

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

What is the correct answer to this question?

The correct answer is: The cluster ID is misconfigured and should be unique per route reflector. — When two route reflectors share the same cluster ID, they treat each other's updates as if from the same cluster. The route reflector loop prevention mechanism drops routes learned from another RR in the same cluster, causing route loss if the clients are not fully meshed.

What should I do if I get this 300-410 question wrong?

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.

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