The answer is that approximately half of the ARP packets are dropped, reducing CPU load but potentially causing reachability issues. This occurs because the CoPP police rate of 1000 pps is set with only a conform-action of 'transmit', and when the current ARP rate exceeds that threshold at 2000 pps, the excess traffic is subject to an implicit drop—Cisco’s default behavior when no explicit exceed-action is configured. On the Cisco DCCOR and CCNP Data Center Core 350-601 exam, this scenario tests your understanding of CoPP policing mechanics and the critical distinction between a policer’s conform and exceed actions; a common trap is assuming that without an exceed-action, excess packets are still forwarded. Remember the memory tip: “No exceed means drop the speed”—if you only define what to do with conforming traffic, the rest is silently discarded, which can break ARP resolution and neighbor reachability.
350-601 Security Practice Question
This 350-601 practice question tests your understanding of security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 Nexus 7000 switch is experiencing high CPU utilization due to control plane traffic. The engineer notices that many packets are being punted to the CPU from the data plane, particularly ARP packets. After examining the CoPP configuration, the engineer sees that the 'arp' class-map is matched in a policy-map with a police rate of 1000 pps and a conform-action of 'transmit'. The current ARP rate is 2000 pps. What is the immediate impact?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Approximately half of the ARP packets are dropped, reducing CPU load but potentially causing reachability issues.
The CoPP policy is configured with a police rate of 1000 pps for ARP packets, but the current ARP rate is 2000 pps. Since the rate exceeds the policer, the conform-action 'transmit' only applies to packets within the rate; excess packets are dropped by default (drop action is implicit when no exceed-action is specified). This results in approximately half of the ARP packets being dropped, which reduces CPU load but can cause ARP resolution failures and reachability issues.
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.
✗
All ARP packets are transmitted normally because the conform-action is 'transmit'.
Why it's wrong here
Only packets within the rate are transmitted; excess are dropped.
✓
Approximately half of the ARP packets are dropped, reducing CPU load but potentially causing reachability issues.
Why this is correct
With 2000 pps against 1000 pps limit, half are dropped.
Related concept
Read the scenario before looking for a memorised answer.
✗
The switch applies an ACL to drop all ARP packets.
Why it's wrong here
CoPP uses class-maps, not ACLs directly for action.
✗
Packets are marked down and transmitted.
Why it's wrong here
No markdown action configured; default exceed is drop.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the implicit default action for excess traffic in CoPP policers—candidates mistakenly assume that only the conform-action matters and that all traffic is transmitted, overlooking that the exceed-action defaults to 'drop' when not explicitly configured.
Detailed technical explanation
How to think about this question
In CoPP, when a policer is configured with only a conform-action (e.g., 'transmit'), the exceed-action defaults to 'drop' per Cisco's implementation. The policer uses a token bucket algorithm: packets within the committed rate (1000 pps) are transmitted, while bursts above that rate are dropped. This behavior is critical for protecting the control plane from DoS attacks, but overly restrictive policing can cause legitimate ARP traffic to be dropped, leading to neighbor discovery failures and network instability.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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: Approximately half of the ARP packets are dropped, reducing CPU load but potentially causing reachability issues. — The CoPP policy is configured with a police rate of 1000 pps for ARP packets, but the current ARP rate is 2000 pps. Since the rate exceeds the policer, the conform-action 'transmit' only applies to packets within the rate; excess packets are dropped by default (drop action is implicit when no exceed-action is specified). This results in approximately half of the ARP packets being dropped, which reduces CPU load but can cause ARP resolution failures and reachability issues.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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