hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures Control Plane Policing…
An engineer configures Control Plane Policing (CoPP) on a router with a policy-map that matches EIGRP packets and sets a police rate of 1000 pps. The class-default is configured with a police rate of 100 pps. Unexpectedly, EIGRP neighbor relationships start flapping, even though the EIGRP packet rate is well below 1000 pps. Which is the most likely explanation?
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 class-map matching EIGRP does not include multicast address 224.0.0.10, causing EIGRP packets to fall into class-default and be policed at 100 pps.
CoPP applies to packets destined to the control plane. EIGRP uses multicast address 224.0.0.10. If the class matching EIGRP does not include the multicast group or uses an incorrect match criterion, EIGRP packets may fall into class-default and be policed at the lower rate (100 pps). This is a common misconfiguration where the ACL or class-map does not properly match EIGRP traffic.
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 class-map matching EIGRP does not include multicast address 224.0.0.10, causing EIGRP packets to fall into class-default and be policed at 100 pps.
Why this is correct
EIGRP uses multicast; if the ACL doesn't match it, CoPP treats it as default traffic.
- ✗
The police rate of 1000 pps is too low for EIGRP hello packets, causing drops.
Why it's wrong here
1000 pps is typically sufficient for EIGRP hellos.
- ✗
CoPP must be applied to the management interface, not the control plane.
Why it's wrong here
CoPP is applied to the control plane using `service-policy input` under control-plane.
- ✗
The class-default police rate must be higher than the EIGRP class rate.
Why it's wrong here
Class-default should be lower, but the issue is misclassification.
Visual reference
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.
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Same concept, more angles
1 more way this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network uses Control Plane Policing (CoPP) to protect the router. Router R1 has CoPP policy applied that rate-limits all traffic to 1 Mbps. R1 shows: 'show policy-map control-plane' indicates drops for EIGRP packets. R1's EIGRP neighbor R2 is flapping. What is the root cause?
hard- ✓ A.The CoPP policy rate-limits EIGRP packets to 1 Mbps, but EIGRP hellos are small and frequent; the rate-limit may still drop them if the policer is not properly configured for burst.
- B.R2 is sending too many EIGRP packets, exceeding the rate-limit.
- C.R1 has an ACL that blocks EIGRP packets before they reach the control plane.
- D.The CoPP policy is applied to the wrong interface.
Why A: EIGRP hello packets are small and sent frequently (every 5 seconds on most LAN interfaces by default). A CoPP policer that rate-limits all traffic to 1 Mbps without an adequate burst parameter will treat the burst of small hello packets as exceeding the committed burst (Bc), causing drops. These drops prevent EIGRP neighbor keepalives from reaching the control plane, leading to neighbor flapping. The root cause is not the total bandwidth but the policer's inability to accommodate the packet-per-second (PPS) burst of small EIGRP hellos.
JA
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.