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300-410 Practice Question: Which TWO actions will prevent a Cisco IOS router…
Which TWO actions will prevent a Cisco IOS router from responding to ICMP echo requests on an interface? (Choose TWO.)
⚠ Common exam trap
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.
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.
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.
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.
- ✗
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.
Why it's wrong here
Incorrect. The 'no ip proxy-arp' disables proxy ARP, which is unrelated to ICMP echo replies.
- ✓
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.
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