The answer is that the CoPP policy is likely using 'match protocol ospf' on a router running OSPFv3, which is not matched by that statement. This is because 'match protocol ospf' in a CoPP class-map only matches OSPFv2 (IPv4) traffic, while OSPFv3 (IPv6) requires a separate match statement, such as 'match protocol ospfv3' or an IPv6 access-list. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how CoPP’s implicit deny-all at the end of the policy-map can silently drop control traffic that isn’t explicitly matched, even when 'show policy-map control-plane' shows no drops—a common trap where engineers assume a matching class is working when it actually isn’t. The key takeaway is that CoPP policies are protocol-version specific, and failing to account for OSPFv3 will cause adjacencies to drop without any visible policer drops. Memory tip: OSPFv2 and OSPFv3 are like two different languages—match only the one your router speaks.
300-410 Route Redistribution Practice Question
This 300-410 practice question tests your understanding of route redistribution. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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).
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
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.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
CoPP can be applied to input or output; OSPF hellos are both sent and received.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
Route Redistribution — This question tests Route Redistribution — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: 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).
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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