- A
The ACL is blocking all BGP traffic from 10.1.1.1.
Why wrong: Line 10 permits BGP traffic from 10.1.1.1, as shown by the matches.
- B
The ACL is permitting DHCP and ICMP echo traffic, but dropping all other traffic.
Lines 20 and 30 permit DHCP and ICMP echo, while line 40 denies everything else, which is typical for CoPP to protect the control plane.
- C
The ACL is applied to the control plane interface and is dropping all traffic.
Why wrong: Only traffic not matching lines 10-30 is dropped; permitted traffic is forwarded.
- D
The ACL has a misconfiguration because the deny statement should be at the top.
Why wrong: The order is correct; permit statements come before the deny all to allow specific traffic.
Question 1,859 of 2,152
Understanding ACL Counters in CoPP Policy
This 300-410 practice question tests your understanding of control plane policing (copp). 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 runs the following command to troubleshoot a Control Plane Policing (CoPP) issue:
R1# show ip access-lists CoPP-ACL
Extended IP access list CoPP-ACL
10 permit tcp host 10.1.1.1 any eq bgp (100 matches)
20 permit udp any any eq 67 (50 matches)
30 permit icmp any any echo (200 matches)
40 deny ip any any (500 matches)What does this output indicate?
Quick Answer
The answer is that the ACL is permitting DHCP and ICMP echo traffic while dropping all other traffic, as indicated by the 500 matches on the final deny ip any any statement. This interpretation is correct because the show ip access-lists CoPP-ACL command displays packet counters for each ACL entry, showing that lines 20 and 30 have matched DHCP (UDP port 67) and ICMP echo requests, while the explicit deny at line 40 catches every unmatched packet—a common design in CoPP policies to protect the control plane from unwanted traffic. On the Cisco CCNP ENARSI 300-410 exam, this tests your ability to read ACL counters in the context of CoPP troubleshooting, where a common trap is assuming that a permit statement with zero matches means the traffic is allowed; in reality, the final deny reveals the true filtering behavior. A useful memory tip is to always check the last line of the ACL output first—if it shows a deny with matches, that is the default action for all traffic not explicitly permitted, making it the key to understanding the policy’s effect.
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 ACL is permitting DHCP and ICMP echo traffic, but dropping all other traffic.
The ACL shows that lines 10, 20, and 30 have match counts, indicating that BGP from 10.1.1.1, DHCP (UDP port 67), and ICMP echo are being permitted. Line 40 is a deny all with 500 matches, meaning all other traffic is being dropped. This confirms that the ACL is permitting only the specified traffic (DHCP and ICMP echo) while dropping everything else, making option B correct.
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.
- ✗
The ACL is blocking all BGP traffic from 10.1.1.1.
Why it's wrong here
Line 10 permits BGP traffic from 10.1.1.1, as shown by the matches.
- ✓
The ACL is permitting DHCP and ICMP echo traffic, but dropping all other traffic.
- ✗
The ACL is applied to the control plane interface and is dropping all traffic.
Why it's wrong here
Only traffic not matching lines 10-30 is dropped; permitted traffic is forwarded.
- ✗
The ACL has a misconfiguration because the deny statement should be at the top.
Why it's wrong here
The order is correct; permit statements come before the deny all to allow specific traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the ability to interpret ACL match counts to determine actual traffic behavior, leading candidates to mistakenly think a deny all at the end means all traffic is dropped, when in fact the permit lines above it are allowing specific traffic.
Trap categories for this question
Command / output trap
Line 10 permits BGP traffic from 10.1.1.1, as shown by the matches.
Detailed technical explanation
How to think about this question
In CoPP, the ACL is applied to the control-plane service-policy to classify traffic for policing actions. The match counts in the ACL are critical for troubleshooting; they increment only when a packet matches that specific line, so seeing 500 matches on the deny line confirms that traffic not matching the permit entries is being dropped. This is often used to protect the control plane from unwanted traffic, such as DHCP floods or ICMP storms, while allowing legitimate BGP sessions.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ACL is permitting DHCP and ICMP echo traffic, but dropping all other traffic. — The ACL shows that lines 10, 20, and 30 have match counts, indicating that BGP from 10.1.1.1, DHCP (UDP port 67), and ICMP echo are being permitted. Line 40 is a deny all with 500 matches, meaning all other traffic is being dropped. This confirms that the ACL is permitting only the specified traffic (DHCP and ICMP echo) while dropping everything else, making option B correct.
What should I do if I get this 300-410 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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Last reviewed: Jul 4, 2026
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