- A
Configure 'no ip unreachables' on the interface.
Why wrong: Incorrect. The 'no ip unreachables' command disables ICMP unreachable messages (e.g., host/network unreachable), not ICMP echo replies.
- B
Apply an inbound access-list on the interface that denies ICMP echo requests.
Correct. An inbound access-list that denies ICMP echo (type 8) will drop incoming ping requests, preventing the router from responding.
- C
Configure 'no ip redirects' on the interface.
Why wrong: Incorrect. The 'no ip redirects' command disables ICMP redirect messages, not echo replies.
- D
Configure 'no ip proxy-arp' on the interface.
Why wrong: Incorrect. The 'no ip proxy-arp' disables proxy ARP, which is unrelated to ICMP echo replies.
- E
Configure 'ip icmp echo-reply disable' globally.
Correct. The 'ip icmp echo-reply disable' global command disables the router from sending ICMP echo replies, effectively preventing responses to pings.
Disabling ICMP Echo Replies: Access-List and Global Command
This 300-410 practice question tests your understanding of device management. 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.
Which TWO actions will prevent a Cisco IOS router from responding to ICMP echo requests on an interface? (Choose TWO.)
Quick Answer
The correct answers are the global command 'ip icmp echo-reply disable' and an inbound access-list with a deny rule for ICMP echo requests. The global command completely disables the router from generating ICMP echo replies on all interfaces, directly addressing the requirement to stop responses to ping. An inbound access-list applied to the interface with a deny statement for ICMP type 8 (echo) blocks the incoming request before the router can process it, effectively preventing the reply. On the Cisco CCNP ENARSI 300-410 exam, this question tests your ability to distinguish between ICMP control-plane features and interface-level traffic filtering—a common trap is confusing 'no ip unreachables' or 'no ip redirects' with echo reply suppression, as those commands affect different ICMP message types. Remember that 'unreachables' and 'redirects' are about error messages, not echo responses. A useful memory tip: think of the global command as a "master switch" for ping replies, while the access-list is a "selective bouncer" at the door.
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
Apply an inbound access-list on the interface that denies ICMP echo requests.
Option B is correct because applying an inbound access-list that denies ICMP echo requests on the interface will cause the router to drop those packets before they reach the processing logic, thus preventing any response. Option E is correct because the global command 'ip icmp echo-reply disable' explicitly disables the router from generating ICMP echo replies, regardless of interface configuration.
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.
- ✗
Configure 'no ip unreachables' on the interface.
Why it's wrong here
Incorrect. The 'no ip unreachables' command disables ICMP unreachable messages (e.g., host/network unreachable), not ICMP echo replies.
- ✓
Apply an inbound access-list on the interface that denies ICMP echo requests.
Why this is correct
Correct. An inbound access-list that denies ICMP echo (type 8) will drop incoming ping requests, preventing the router from responding.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Configure 'no ip redirects' on the interface.
Why it's wrong here
Incorrect. The 'no ip redirects' command disables ICMP redirect messages, not echo replies.
- ✗
Configure 'no ip proxy-arp' on the interface.
- ✓
Configure 'ip icmp echo-reply disable' globally.
Why this is correct
Correct. The 'ip icmp echo-reply disable' global command disables the router from sending ICMP echo replies, effectively preventing responses to pings.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between ICMP control messages (unreachables, redirects) and ICMP echo messages, so candidates mistakenly choose 'no ip unreachables' or 'no ip redirects' thinking they affect ping responses.
Trap categories for this question
Command / output trap
Incorrect. The 'no ip unreachables' command disables ICMP unreachable messages (e.g., host/network unreachable), not ICMP echo replies.
Detailed technical explanation
How to think about this question
ICMP echo requests are processed by the router's IP stack at the network layer; an inbound access-list filters packets before they reach the routing or process-switching path, effectively preventing the router from even seeing the echo request. The 'ip icmp echo-reply disable' command is a global Cisco IOS feature that suppresses the generation of echo replies at the system level, overriding any interface-level settings. In real-world scenarios, disabling ICMP echo replies is a common security hardening step to prevent reconnaissance, but it must be balanced with the need for network troubleshooting.
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.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Apply an inbound access-list on the interface that denies ICMP echo requests. — Option B is correct because applying an inbound access-list that denies ICMP echo requests on the interface will cause the router to drop those packets before they reach the processing logic, thus preventing any response. Option E is correct because the global command 'ip icmp echo-reply disable' explicitly disables the router from generating ICMP echo replies, regardless of interface configuration.
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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