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.
300-410 Control Plane Policing (CoPP) Practice Question
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)
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 traffic matching various protocols. The 'deny ip any any' at line 40 indicates that all unmatched traffic is being denied, which could be part of a CoPP policy to drop unwanted traffic to the control plane.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Why this is correct
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.
Related concept
Standard ACLs match source addresses.
✗
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: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
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
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
Control Plane Policing (CoPP) — This question tests Control Plane Policing (CoPP) — Standard ACLs match source addresses..
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 traffic matching various protocols. The 'deny ip any any' at line 40 indicates that all unmatched traffic is being denied, which could be part of a CoPP policy to drop unwanted traffic to the control plane.
What should I do if I get this 300-410 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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