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300-410 Practice Question: An engineer configures Control Plane Policing…
An engineer configures Control Plane Policing (CoPP) on a router to protect the control plane. After applying the policy, OSPF adjacencies go down. The policy includes a class that matches OSPF traffic with a police rate of 1000 pps. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the misconception that CoPP only affects management traffic, but the trap here is that class-default can inadvertently drop critical routing protocol packets if not properly configured, leading to adjacency loss.
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 OSPF traffic is matched by class-default, which has a low police rate or is set to drop, causing hello packets to be dropped.
When CoPP is applied, any traffic not explicitly matched by a user-defined class falls into class-default. If class-default has a low police rate or is configured to drop packets, OSPF hello packets (which are critical for adjacency maintenance) will be dropped, causing OSPF adjacencies to go down. The OSPF traffic is likely not being matched by the intended class due to incorrect classification or ordering, leaving it to be processed by class-default.
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 OSPF traffic is matched by class-default, which has a low police rate or is set to drop, causing hello packets to be dropped.
Why this is correct
If OSPF is not explicitly matched in a higher class, it falls to class-default, which may have a restrictive policy.
- ✗
The police rate of 1000 pps is too low for OSPF hello packets.
Why it's wrong here
OSPF hello packets are small and infrequent; 1000 pps is more than sufficient.
- ✗
CoPP only applies to management traffic, not routing protocols.
Why it's wrong here
CoPP applies to all control plane traffic, including routing protocols.
- ✗
The OSPF process is not configured to use the control plane policy.
Why it's wrong here
CoPP is applied globally to the control plane, not per process.
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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