hardMultiple Choice
300-410 Practice Question: An engineer configures Control Plane Policing…
An engineer configures Control Plane Policing (CoPP) on a router running OSPF. After applying the policy, OSPF neighbors intermittently drop and recover. The CoPP policy includes a class-map matching OSPF traffic with a police rate of 64000 bps. The router has multiple OSPF neighbors and the link utilization is normal. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the misconception that a bps-based police rate is sufficient for small-packet protocols like OSPF, leading candidates to overlook the packet-per-second (pps) limitation that causes drops.
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 police rate is in bits per second, but OSPF hello packets are small; the packet-per-second rate is exceeded, causing drops.
OSPF hello packets are small (typically 44–64 bytes), so a police rate of 64000 bps translates to a very low packet-per-second (pps) allowance. When multiple OSPF neighbors send hellos and other OSPF packets, the pps limit is easily exceeded, causing CoPP to drop packets and disrupt neighbor adjacencies. This is the most likely cause of intermittent OSPF neighbor drops despite normal link utilization.
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 CoPP policy uses the default class class-default, which drops OSPF packets.
Why it's wrong here
class-default only matches traffic not caught by earlier classes; it does not inherently drop OSPF, and the stem already defines a dedicated OSPF class. It tempts because unmatched traffic can be policed or dropped by class-default, which is correct when no explicit class captures the protocol.
- ✓
The police rate is in bits per second, but OSPF hello packets are small; the packet-per-second rate is exceeded, causing drops.
Why this is correct
CoPP polices in bits per second, so 64000 bps allows roughly 128 small OSPF hello packets per second. With multiple neighbours sending frequent hellos, the packet rate exceeds this, causing intermittent drops and adjacency resets.
- ✗
OSPF uses UDP, and CoPP only filters TCP traffic.
Why it's wrong here
OSPF runs directly over IP protocol 89, not UDP, so a TCP-only filter claim is factually wrong; CoPP matches protocol 89 via ACLs. It tempts because many control-plane protocols (BGP, TACACS, SNMP) do use TCP or UDP, making transport-based class-maps familiar.
- ✗
The CoPP policy is applied to the wrong interface; it should be applied to the management interface.
Why it's wrong here
CoPP is a control-plane policy applied globally via the control-plane service, not to any interface; interface placement is invalid. It is tempting because interface-level policy application is the norm for QoS and ACLs, and would be right for filtering transit traffic on a management link.
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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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.