The answer is an inbound ACL on the interface that denies ICMP from 10.10.10.1. This is correct because Telnet and ICMP are controlled by different ACL application points: Telnet traffic is filtered by the VTY access-class applied to the router’s management lines, while ICMP echo requests are processed by the interface ACL applied inbound on the router’s physical or virtual interface. Since the management station can telnet successfully, the VTY ACL is correctly permitting 10.10.10.0/24, but the router’s failure to respond to pings indicates that an interface ACL is blocking ICMP before it reaches the control plane. On the CCNP ENARSI 300-410 exam, this scenario tests your understanding of ACL placement and the distinction between management-plane and data-plane filtering—a common trap is assuming a VTY ACL controls all traffic to the router. Remember the memory tip: “Telnet talks to VTY, but ICMP hits the interface first.”
300-410 Device Management Practice Question
This 300-410 practice question tests your understanding of device management. 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 a router that is not responding to ICMP echo requests from a management station at 10.10.10.1. The router has an ACL applied to the VTY lines that permits only 10.10.10.0/24. The engineer can telnet to the router from the management station. What is the most likely cause?
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
✓
An inbound ACL on the interface denies ICMP from 10.10.10.1.
Telnet is permitted by the VTY ACL, but ICMP is controlled by an interface ACL or the global 'ip icmp rate-limit' feature. The most likely cause is an inbound ACL on the interface that denies ICMP from the management station.
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.
An inbound ACL on the interface denies ICMP from 10.10.10.1.
Why this is correct
Since Telnet works, the VTY ACL is not the issue; an interface ACL blocking ICMP is the likely cause.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The router has 'no ip icmp echo' configured globally.
Why it's wrong here
There is no such global command; ICMP echo responses are controlled by interface ACLs or the 'ip icmp rate-limit' feature.
✗
The management station is not in the routing table of the router.
Why it's wrong here
If the management station were not reachable, Telnet would also fail.
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
There is no such global command; ICMP echo responses are controlled by interface ACLs or the 'ip icmp rate-limit' feature.
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.
Device Management — This question tests Device Management — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: An inbound ACL on the interface denies ICMP from 10.10.10.1. — Telnet is permitted by the VTY ACL, but ICMP is controlled by an interface ACL or the global 'ip icmp rate-limit' feature. The most likely cause is an inbound ACL on the interface that denies ICMP from the management station.
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.
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?
Standard ACLs match source addresses.
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