The answer is that the packet is denied. This occurs because Cisco IOS-XE automatically appends an implicit deny any statement to the end of every IPv4 ACL, meaning that if no preceding permit or deny entries match the packet, this final rule triggers and drops the traffic. This behavior is fundamental to ACL security design, ensuring that only explicitly permitted traffic is allowed through an inbound interface. On the Cisco CCNP ENARSI 300-410 exam, this concept often appears in questions about ACL evaluation order or troubleshooting denied traffic, with a common trap being that candidates forget the implicit deny exists and assume unmatched packets are allowed. A reliable memory tip is to think of ACLs as a bouncer: if you don’t have a permit on the list, you’re automatically denied at the door.
300-410 IPv4 Access Control Lists Practice Question
This 300-410 practice question tests your understanding of ipv4 access control lists. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
By default in Cisco IOS-XE, what is the behavior of an IPv4 ACL when no entries match and the ACL is applied to an inbound interface?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The packet is denied.
By default, Cisco IOS-XE applies an implicit 'deny any' statement at the end of every IPv4 ACL. If no entries match the packet, the implicit deny triggers, and the packet is dropped. This behavior is consistent for ACLs applied to inbound interfaces, ensuring that only explicitly permitted traffic is allowed.
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 packet is permitted.
Why it's wrong here
The implicit deny all causes unmatched packets to be dropped.
✓
The packet is denied.
Why this is correct
The implicit deny all at the end of every IPv4 ACL denies unmatched traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
The packet is forwarded based on routing table lookup.
Why it's wrong here
ACL processing occurs before routing; unmatched packets are denied.
✗
The ACL logs the packet and continues.
Why it's wrong here
No implicit logging exists; the packet is simply denied.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the implicit deny any behavior by presenting scenarios where an ACL has no matching entries, leading candidates to mistakenly think the packet is permitted or forwarded based on routing.
Detailed technical explanation
How to think about this question
The implicit deny any is a fundamental security feature of Cisco IOS ACLs, defined in RFC 1700 and implemented as a hidden entry at the end of every ACL. When an ACL is applied inbound, the packet is evaluated against the ACL before any routing lookup; if no permit statement matches, the packet is silently dropped unless a 'permit any' or 'deny any log' is explicitly configured. In real-world scenarios, forgetting to add a 'permit ip any any' at the end of an ACL can cause unintended traffic drops, a common issue during network migrations.
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.
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The packet is denied. — By default, Cisco IOS-XE applies an implicit 'deny any' statement at the end of every IPv4 ACL. If no entries match the packet, the implicit deny triggers, and the packet is dropped. This behavior is consistent for ACLs applied to inbound interfaces, ensuring that only explicitly permitted traffic is allowed.
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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Question Discussion
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