The answer is to increase the policer rate for the default class in the CoPP policy. This is correct because the default class in a CoPP policy acts as a catch-all for any control-plane traffic not explicitly matched by higher-priority classes; when you see CoPP default class drops, it means the aggregate policer rate for that unmatched traffic is too low, causing legitimate packets like ARP or BFD to be dropped. On the Cisco DCCOR / CCNP Data Center Core 350-601 exam, this scenario tests your understanding of how CoPP class-maps prioritize critical protocols—increasing the default class rate safely absorbs the overflow without touching the dedicated policers for OSPF or BGP, thus preserving routing protocol stability. A common trap is to mistakenly adjust a protocol-specific class, which could destabilize routing; instead, remember the memory tip: “Default drops? Raise the default rate—don’t touch the VIPs.”
350-601 Security Practice Question
This 350-601 practice question tests your understanding of security. 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.
A network engineer is troubleshooting CoPP drops on a Cisco Nexus 9000 switch. The 'show control-plane' output indicates that packets are being dropped due to 'CoPP' on the 'default' control-plane class. Which action is most likely to resolve the issue without affecting routing protocol stability?
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
✓
Increase the policer rate for the 'default' class in the CoPP policy.
The 'default' class in a CoPP policy catches all control-plane traffic not explicitly matched by higher-priority classes. Drops in this class indicate that the aggregate policer rate for unmatched traffic is too low. Increasing the policer rate for the 'default' class allows more legitimate control-plane packets (e.g., ARP, BFD, or management traffic) to pass without impacting the dedicated policers for critical protocols like OSPF or BGP, thus preserving routing stability.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Disable CoPP globally to allow all control-plane traffic.
Why it's wrong here
Disabling CoPP removes protection against DoS attacks.
✓
Increase the policer rate for the 'default' class in the CoPP policy.
Why this is correct
Raising the policer rate allows more packets to pass, reducing drops.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Modify the class-map to reclassify the dropped packets to a higher priority class.
Why it's wrong here
Reclassification may starve other traffic and is not a direct fix.
✗
Increase the ingress buffer size on the control-plane interface.
Why it's wrong here
Buffering only delays drops, does not solve policer drops.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that all CoPP drops indicate a need to reclassify traffic to a higher priority class, when in fact the 'default' class drop is a classic sign of an undersized catch-all policer that simply needs a rate adjustment.
Detailed technical explanation
How to think about this question
CoPP uses a Modular QoS CLI (MQC) policy applied to the control-plane, where each class has a policer (typically a single-rate two-color marker). The 'default' class acts as a catch-all with a low default rate (e.g., 200 pps on Nexus 9000). In real-world scenarios, legitimate traffic like ICMP unreachables or DHCP renewals can accumulate in this class; increasing the policer rate to a safe value (e.g., 1000 pps) based on baseline monitoring resolves drops without compromising security.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the policer rate for the 'default' class in the CoPP policy. — The 'default' class in a CoPP policy catches all control-plane traffic not explicitly matched by higher-priority classes. Drops in this class indicate that the aggregate policer rate for unmatched traffic is too low. Increasing the policer rate for the 'default' class allows more legitimate control-plane packets (e.g., ARP, BFD, or management traffic) to pass without impacting the dedicated policers for critical protocols like OSPF or BGP, thus preserving routing stability.
What should I do if I get this 350-601 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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