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300-410 Practice Question: A network uses route summarization to reduce…
A network uses route summarization to reduce routing table size. After enabling Flexible NetFlow, some routes that were previously summarized are now being advertised individually. Router R1 has: interface GigabitEthernet0/0 ip summary-address eigrp 100 10.0.0.0 255.0.0.0. The flow monitor is applied to the same interface. show ip route eigrp | include (10.0.0.0/8) shows the summary route, but also shows more specific routes like 10.1.0.0/16. What is the root cause?
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 flow monitor is configured with a sampler that causes the router to process packets in software, and the software path learns more specific routes from routing updates that are not summarized.
Flexible NetFlow can cause the router to process packets differently, but it should not affect route summarization. However, if the flow monitor is configured with a flow record that includes the 'ipv4 source prefix' or 'ipv4 destination prefix' fields, it might cause the router to install more specific routes in the routing table due to the way the router handles flow cache entries. The correct answer is that the flow monitor is using a flow record that includes the 'ipv4 destination prefix' field, and the router is using that to create a route cache that overrides the summary route. But this is not standard behavior. The more likely root cause is that the summary route is configured on the interface, but the flow monitor is applied in the input direction, and the router's CEF (Cisco Express Forwarding) is affected by the flow monitor, causing it to punt packets to the CPU, which then learns more specific routes via the routing protocol. Actually, the correct answer is that the flow monitor is configured with a sampler that causes the router to process packets in software, and the software path learns more specific routes from the routing updates that are not summarized.
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 sampler that causes the router to process packets in software, and the software path learns more specific routes from routing updates that are not summarized.
Why this is correct
When a sampler is used, packets are punted to the CPU for sampling, and the CPU may process routing updates that contain more specific routes, which are then installed in the routing table, bypassing the summary.
- ✗
The flow monitor is using a flow record that includes the 'ipv4 destination prefix' field, causing the router to install a route for each destination.
Why it's wrong here
Flow records do not install routes.
- ✗
The summary route is not configured correctly; it should be a range of /8, but the more specific routes are from a different EIGRP process.
Why it's wrong here
The summary route is configured, but the more specific routes appear, indicating a leak.
- ✗
The flow exporter is sending the more specific routes to the collector, which then redistributes them back.
Why it's wrong here
The collector does not inject routes into the routing table.
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.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
BGP Route Aggregation
BGP Route Aggregation is a technique that combines multiple specific network routes into a single summary route to reduce the size of routing tables and improve network efficiency.
Key term
NetFlow Configuration
NetFlow Configuration is the process of setting up Cisco devices to collect and export metadata about network traffic flows for monitoring, analysis, and troubleshooting.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.