- A
The flow monitor is configured with a flow record that includes the 'bgp next-hop' field, causing the route reflector to change the next-hop to itself, which is not reachable by clients.
Why wrong: Incorrect. Flexible NetFlow flow monitors do not modify BGP attributes like next-hop. The 'bgp next-hop' field in a flow record is for recording purposes only and does not affect BGP path selection.
- B
The flow exporter is configured to use the BGP neighbor's IP as the destination, but the exporter is not reachable, causing BGP updates to be delayed.
Why wrong: Incorrect. The flow exporter's reachability is unrelated to BGP update delivery. BGP sessions are established over TCP, and flow exporter configuration does not delay or interrupt BGP advertisements.
- C
The flow monitor is applied to the BGP peering interface in the input direction, and it uses a match ip address prefix-list that denies the prefix 10.1.1.0/24, causing the route reflector to not process the route.
Why wrong: Incorrect. Flexible NetFlow flow monitors only capture flow statistics; they do not filter or drop routing updates. A match ip address prefix-list in a flow record does not affect BGP route processing.
- D
The BGP route reflector is configured with a cluster ID that conflicts with the flow monitor's settings.
Correct. A cluster ID conflict prevents the route reflector from reflecting routes that already contain its own cluster ID, even though the routes are present in the BGP table.
Flexible NetFlow Interference with BGP Route Reflection
This 300-410 practice question tests your understanding of netflow and flexible netflow. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. A key principle to apply: cluster ID. 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 BGP-based network uses route reflectors and Flexible NetFlow to monitor traffic. After applying a flow monitor to the route reflector's interface, some BGP routes are not being reflected to clients. Router R1 (route reflector) shows: show bgp vpnv4 unicast all neighbors 10.0.0.2 advertised-routes | include (10.1.1.0/24) No entries. The BGP session is up, and the route 10.1.1.0/24 is in the BGP table. What is the root cause?
Quick Answer
The answer is a misconfigured flow monitor applied to the BGP peering interface in the input direction, using a match ip address prefix-list that denies the prefix 10.1.1.0/24, which prevents the route reflector from processing and reflecting the route. This occurs because Flexible NetFlow, when applied to an interface, can intercept incoming BGP updates before they reach the BGP process; if the flow monitor’s match statement filters the prefix, the router never installs or advertises it to clients, even though the BGP session remains up and the route exists in the table. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how control-plane traffic interacts with data-plane monitoring features—a common trap is assuming BGP filtering only happens via route-maps or prefix-lists, overlooking that a flow monitor’s match clause can silently drop updates. Remember the memory tip: “Flow before BGP—if the monitor denies it, the reflector never sees it.”
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 BGP route reflector is configured with a cluster ID that conflicts with the flow monitor's settings.
The root cause is a cluster ID conflict. Route reflectors use a cluster ID to prevent routing loops. If the route reflector receives a BGP update that already contains its own cluster ID in the cluster list, it will not reflect that route to clients, even though the route is present in the BGP table. This explains why 10.1.1.0/24 appears in the BGP table but is not advertised to neighbors. The other options are incorrect because Flexible NetFlow flow monitors do not filter or modify BGP updates, and exporter reachability does not affect BGP advertisements.
Key principle: Cluster ID
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 flow monitor is configured with a flow record that includes the 'bgp next-hop' field, causing the route reflector to change the next-hop to itself, which is not reachable by clients.
Why it's wrong here
Incorrect. Flexible NetFlow flow monitors do not modify BGP attributes like next-hop. The 'bgp next-hop' field in a flow record is for recording purposes only and does not affect BGP path selection.
- ✗
The flow exporter is configured to use the BGP neighbor's IP as the destination, but the exporter is not reachable, causing BGP updates to be delayed.
- ✗
The flow monitor is applied to the BGP peering interface in the input direction, and it uses a match ip address prefix-list that denies the prefix 10.1.1.0/24, causing the route reflector to not process the route.
Why it's wrong here
Incorrect. Flexible NetFlow flow monitors only capture flow statistics; they do not filter or drop routing updates. A match ip address prefix-list in a flow record does not affect BGP route processing.
- ✓
The BGP route reflector is configured with a cluster ID that conflicts with the flow monitor's settings.
Why this is correct
Correct. A cluster ID conflict prevents the route reflector from reflecting routes that already contain its own cluster ID, even though the routes are present in the BGP table.
Related concept
Cluster ID
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common trap is assuming that Flexible NetFlow flow monitors can filter BGP updates. In reality, flow monitors only capture traffic statistics and do not interfere with control plane packets like BGP updates.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Cluster ID
- Route Reflection
- Flexible NetFlow
- BGP Table vs. Advertising
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
Cluster ID
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review cluster ID, then practise related 300-410 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this 300-410 question test?
NetFlow and Flexible NetFlow — This question tests NetFlow and Flexible NetFlow — Cluster ID.
What is the correct answer to this question?
The correct answer is: The BGP route reflector is configured with a cluster ID that conflicts with the flow monitor's settings. — The root cause is a cluster ID conflict. Route reflectors use a cluster ID to prevent routing loops. If the route reflector receives a BGP update that already contains its own cluster ID in the cluster list, it will not reflect that route to clients, even though the route is present in the BGP table. This explains why 10.1.1.0/24 appears in the BGP table but is not advertised to neighbors. The other options are incorrect because Flexible NetFlow flow monitors do not filter or modify BGP updates, and exporter reachability does not affect BGP advertisements.
What should I do if I get this 300-410 question wrong?
Review cluster ID, then practise related 300-410 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Cluster ID
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Last reviewed: Jun 19, 2026
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