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300-410 Practice Question: An engineer applies a CoPP policy to a router to…
An engineer applies a CoPP policy to a router to protect the control plane. The policy includes a class-map that matches all ICMP traffic and polices it to 5000 bps. After the policy is applied, the engineer notices that OSPF adjacencies are going down. The OSPF hello packets are not being received. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the trap that candidates assume only the explicitly matched class affects traffic, forgetting that the default class in a CoPP policy drops all unmatched traffic unless explicitly configured otherwise.
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 CoPP policy has a default class that drops all unmatched traffic, including OSPF packets.
The CoPP policy includes a class-map that matches only ICMP traffic, but when applied, it uses a default class that drops all unmatched traffic. OSPF hello packets, which are not ICMP, fall into this default class and are dropped, causing adjacencies to fail. This is a common misconfiguration where the policy lacks an explicit permit for essential control plane protocols like OSPF.
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 is policing OSPF packets because the class-map matches all IP traffic, not just ICMP.
Why it's wrong here
The scenario says the class-map matches ICMP traffic; OSPF uses IP protocol 89, so it should not be matched unless the class-map is misconfigured.
- ✓
The CoPP policy has a default class that drops all unmatched traffic, including OSPF packets.
Why this is correct
If the CoPP policy does not explicitly permit OSPF packets, a default drop class will cause OSPF adjacencies to fail.
- ✗
The OSPF hello packets are being rate-limited because they are ICMP packets.
Why it's wrong here
OSPF packets are not ICMP; they are IP protocol 89.
- ✗
The CoPP policy is applied to the wrong interface, causing OSPF packets to be dropped.
Why it's wrong here
CoPP is applied to the control plane, not interfaces. This is a common misconception.
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
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