Quick Answer
The correct answer is that only ICMP echo and echo-reply are permitted, while all other IP traffic is denied. This is because the ACL explicitly permits only ICMP type 8 (echo) and type 0 (echo-reply) with the first two entries, and the final deny ip any any statement acts as an implicit catch-all, blocking every other IP protocol and ICMP type—including destination unreachable, time-exceeded, or traceroute packets. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of ACL sequence logic and the critical role of the explicit deny any any, which is often used to override the default implicit deny for visibility in match counters. A common trap is assuming that permitting echo and echo-reply allows all ICMP traffic; in reality, only those two types pass. Remember the memory tip: “Echo in, Echo out—everything else is thrown out.”
This 300-410 practice question tests your understanding of ipv4 access control lists. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 on Router R1:
R1# show ip access-lists
Extended IP access list 170
10 permit icmp any any echo (100 matches)
20 permit icmp any any echo-reply (80 matches)
30 deny ip any any (10 matches)Based on this output, which statement is correct?
All ICMP traffic is permitted.
Why wrong: Only echo and echo-reply are permitted; other ICMP types are denied.
Only ICMP echo and echo-reply are permitted; all other IP traffic is denied.
Line 30 denies all other IP traffic, including other ICMP types.
The ACL permits all IP traffic.
Why wrong: Line 30 denies all other IP traffic.
The ACL is not applied.
Why wrong: Match counts indicate it is applied.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Only ICMP echo and echo-reply are permitted; all other IP traffic is denied.
The ACL 170 explicitly permits only ICMP echo (type 8) and echo-reply (type 0) traffic, as shown by the match counters. The final deny ip any any statement blocks all other IP traffic, including other ICMP types and non-ICMP IP protocols. Therefore, only ICMP echo and echo-reply are permitted; all other IP traffic is denied, 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
For each option: why learners choose it and why it is or isn't the right answer here.
All ICMP traffic is permitted.
Why it's wrong here
Only echo and echo-reply are permitted; other ICMP types are denied.
Only ICMP echo and echo-reply are permitted; all other IP traffic is denied.
Why this is correct
Line 30 denies all other IP traffic, including other ICMP types.
Related concept
Read the scenario before looking for a memorised answer.
The ACL permits all IP traffic.
Why it's wrong here
Line 30 denies all other IP traffic.
The ACL is not applied.
Why it's wrong here
Match counts indicate it is applied.
Common exam traps
Cisco often tests the misconception that an ACL with only two permit statements for specific ICMP types permits all ICMP traffic, but the explicit or implicit deny ip any any at the end blocks all other ICMP types and non-ICMP IP traffic.
Detailed technical explanation
In Cisco IOS, an ACL without an explicit permit statement for a specific protocol or ICMP type will be denied by the implicit deny ip any any at the end, but here the engineer added an explicit deny ip any any for visibility (match counter). The match counters increment only when the ACL is applied to an interface (inbound or outbound) and traffic matches a line; this confirms the ACL is active. In real-world scenarios, forgetting to permit essential ICMP types like destination unreachable can break Path MTU Discovery, causing connectivity issues.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
The correct answer is: Only ICMP echo and echo-reply are permitted; all other IP traffic is denied. — The ACL 170 explicitly permits only ICMP echo (type 8) and echo-reply (type 0) traffic, as shown by the match counters. The final deny ip any any statement blocks all other IP traffic, including other ICMP types and non-ICMP IP protocols. Therefore, only ICMP echo and echo-reply are permitted; all other IP traffic is denied, making option B correct.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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