The correct answer is that only IPv6 ping traffic is permitted inbound on GigabitEthernet0/0, while all other IPv6 traffic is dropped. This is because the IPv6 ACL explicitly permits ICMP echo-request and echo-reply messages—the two packet types that constitute a standard IPv6 ping—and then denies all other IPv6 traffic with the final implicit deny any any. The `ipv6 traffic-filter` command applies this ACL inbound, meaning the router evaluates every incoming packet against the permit statements before the deny rule. On the ENCOR 350-401 exam, this configuration tests your understanding of how IPv6 ACLs filter ICMPv6 traffic and the critical difference between an ACL applied with `ipv6 traffic-filter` versus `ipv6 access-group` (which is for IPv4). A common trap is assuming the implicit deny is absent or that the ACL must explicitly block all other protocols; in reality, the explicit `deny ipv6 any any` is redundant but clarifies the behavior. Memory tip: think of the ACL as a bouncer who only lets in two specific ICMP party guests—echo-request and echo-reply—and turns everyone else away at the door.
350-401 Infrastructure Security Practice Question
This 350-401 practice question tests your understanding of infrastructure security. 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 IPv6 access-list on a Cisco IOS-XE router:
```
ipv6 access-list PERMIT_ICMP
permit icmp any any echo-request
permit icmp any any echo-reply
deny ipv6 any any
!
interface GigabitEthernet0/0
ipv6 traffic-filter PERMIT_ICMP in
```
What is the effect of this configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Only IPv6 ping (echo-request and echo-reply) is allowed inbound on Gi0/0; all other IPv6 traffic is dropped.
The IPv6 ACL permits only ICMP echo-request and echo-reply (ping) and denies all other IPv6 traffic. It is applied inbound on Gi0/0.
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.
✓
Only IPv6 ping (echo-request and echo-reply) is allowed inbound on Gi0/0; all other IPv6 traffic is dropped.
Why this is correct
Correct. The ACL permits only those two ICMP types and denies everything else.
Related concept
Standard ACLs match source addresses.
✗
All ICMPv6 traffic is permitted inbound on Gi0/0.
Why it's wrong here
Incorrect. Only echo-request and echo-reply are permitted.
✗
The ACL is applied outbound, so it filters traffic leaving Gi0/0.
Why it's wrong here
Incorrect. The 'in' keyword applies it inbound.
✗
The ACL permits all IPv6 traffic because the deny statement is at the end.
Why it's wrong here
Incorrect. The deny statement blocks all other traffic.
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
Keyword trap
Incorrect. The 'in' keyword applies it inbound.
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 350-401 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 350-401 ACL questions on filtering logic and placement.
Infrastructure Security — This question tests Infrastructure Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Only IPv6 ping (echo-request and echo-reply) is allowed inbound on Gi0/0; all other IPv6 traffic is dropped. — The IPv6 ACL permits only ICMP echo-request and echo-reply (ping) and denies all other IPv6 traffic. It is applied inbound on Gi0/0.
What should I do if I get this 350-401 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 350-401 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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 350-401 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 350-401 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.