Question 1,276 of 2,152

BGP Troubleshooting →hardMultiple ChoiceObjective-mapped

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.

300-410 BGP Troubleshooting Practice Question

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.

Question 1hardmultiple choice

Open the full BGP breakdown →

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 →

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: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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
Static NAT maps one inside address to one outside address.
✗
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: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

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

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

Real-world example

How this comes up in practice

A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

What to study next

Got this wrong? Here's your next step.

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.

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FAQ

Questions learners often ask

What does this 300-410 question test?

BGP Troubleshooting — This question tests BGP Troubleshooting — Static NAT maps one inside address to one outside address..

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?

Static NAT maps one inside address to one outside address.

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