The correct answer is that the ACL blocks ICMP echo-request and echo-reply, but permits all other IPv6 traffic inbound. This is because the IPv6 ACL named BLOCK-ICMP explicitly denies ICMPv6 echo-request (type 128) and echo-reply (type 129) packets, while the final permit ipv6 any any statement ensures all other IPv6 traffic is allowed through. On the Cisco CCNP ENARSI 300-410 exam, this configuration tests your understanding of how ipv6 traffic-filter applies ACLs to filter specific ICMPv6 message types at the interface level, a common scenario for securing network management traffic without disrupting normal IPv6 routing. A frequent trap is forgetting that IPv6 uses ICMPv6 for essential functions like Neighbor Discovery, so blocking all ICMPv6 would break connectivity; here, only echo types are denied. Memory tip: think of "128 and 129, ping is blocked, but the rest is fine."
300-410 IPv6 Traffic Filtering and uRPF Practice Question
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. 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.
Consider the following configuration:
ipv6 access-list BLOCK-ICMP
deny icmp any any echo-request
deny icmp any any echo-reply
permit ipv6 any any
interface GigabitEthernet0/2
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ACL blocks ICMP echo-request and echo-reply, but permits all other IPv6 traffic inbound.
Option A is correct because the IPv6 ACL explicitly denies ICMPv6 echo-request and echo-reply messages (types 128 and 129) while the final permit ipv6 any any statement allows all other IPv6 traffic. The ipv6 traffic-filter command applied inbound on GigabitEthernet0/2 filters traffic as it enters the interface, so only the specified ICMP types are blocked, and all other IPv6 traffic is permitted.
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.
✓
The ACL blocks ICMP echo-request and echo-reply, but permits all other IPv6 traffic inbound.
Why this is correct
The deny statements match the specified ICMP types; the final permit allows everything else.
Related concept
Read the scenario before looking for a memorised answer.
✗
The ACL blocks all ICMPv6 traffic because the deny statements are too broad.
Why it's wrong here
Only echo-request and echo-reply are denied; other ICMP types (e.g., neighbor solicitation) are permitted.
✗
The ACL must be applied outbound to filter echo-request.
Why it's wrong here
Inbound filtering is correct; echo-request arriving on the interface will be matched.
✗
The ACL is missing the 'log' keyword to be effective.
Why it's wrong here
The 'log' keyword is optional and not required for the ACL to function.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that an ACL applied inbound cannot block echo-reply because it is a response, but in IPv6, echo-reply is a separate ICMP type that can be filtered inbound on the interface where it arrives.
Trap categories for this question
Keyword trap
The 'log' keyword is optional and not required for the ACL to function.
Detailed technical explanation
How to think about this question
ICMPv6 echo-request and echo-reply correspond to ICMPv6 type 128 and type 129, respectively. The IPv6 ACL uses the 'icmp' protocol keyword and can filter by ICMP type and code; without specifying a type, 'deny icmp any any' would block all ICMPv6. The ipv6 traffic-filter command is the IPv6 equivalent of the ip access-group command for IPv4, and it can be applied inbound or outbound on an interface. In real-world scenarios, blocking ICMP echo-request inbound on external interfaces is a common security practice to prevent ping sweeps, while still allowing other ICMPv6 messages like neighbor discovery (ND) for proper IPv6 operation.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPv6 Traffic Filtering and uRPF — This question tests IPv6 Traffic Filtering and uRPF — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ACL blocks ICMP echo-request and echo-reply, but permits all other IPv6 traffic inbound. — Option A is correct because the IPv6 ACL explicitly denies ICMPv6 echo-request and echo-reply messages (types 128 and 129) while the final permit ipv6 any any statement allows all other IPv6 traffic. The ipv6 traffic-filter command applied inbound on GigabitEthernet0/2 filters traffic as it enters the interface, so only the specified ICMP types are blocked, and all other IPv6 traffic is permitted.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.