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300-410 Practice Question: An engineer applies a Control Plane Policing…
An engineer applies a Control Plane Policing (CoPP) policy to a router. After applying, OSPF adjacencies go down. The policy has a class that matches OSPF traffic with a police rate of 1000 pps. The 'show policy-map control-plane' shows no drops. 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 CoPP policy uses 'match protocol ospf' but the router runs OSPFv3, which is not matched by that statement.
CoPP policies have an implicit 'deny all' at the end. If the OSPF traffic is not matched by any class, it will be dropped by the implicit deny. However, the engineer may have configured a class that matches OSPF but the police rate is in bps, not pps, causing OSPF hellos to be dropped if they exceed the rate. But the question states no drops, so the issue is likely that the OSPF class is not matching due to incorrect match criteria (e.g., match protocol ospf vs match access-group).
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 'match protocol ospf' but the router runs OSPFv3, which is not matched by that statement.
Why this is correct
OSPFv3 uses IPv6; 'match protocol ospf' matches OSPFv2 only.
- ✗
The police rate is configured in bps instead of pps, causing OSPF hellos to be dropped.
Why it's wrong here
If no drops are seen, rate is not the issue.
- ✗
The 'class class-default' is configured with a police rate that drops all traffic.
Why it's wrong here
Class-default would affect all traffic, but OSPF might still be matched earlier.
- ✗
The CoPP policy is applied to the input direction, but OSPF packets are sent from the router.
Why it's wrong here
CoPP can be applied to input or output; OSPF hellos are both sent and received.
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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