The answer is that VACLs cannot filter intra-VLAN traffic because they only enforce policies at VLAN boundaries. VLAN ACLs operate as a Layer 2 security mechanism that inspects traffic as it enters or exits a VLAN, but they are bypassed when frames are bridged between ports within the same VLAN—this traffic never reaches the VACL enforcement point. On the Cisco DCCOR and CCNP Data Center Core 350-601 exam, this limitation is a classic trap: you might see a scenario where a VACL is correctly applied yet fails to block same-VLAN communication, testing your understanding that VACLs are strictly inter-VLAN filters. A common memory tip is to think of VACLs as “VLAN boundary guards” that only stop traffic crossing into or out of the VLAN, not traffic already inside it. For intra-VLAN filtering, you would need a port ACL (PACL) or private VLANs instead.
350-601 Security Practice Question
This 350-601 practice question tests your understanding of 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.
During a security audit, you discover that a Cisco Nexus 9000 switch is allowing traffic between two ports in the same VLAN despite having a VLAN ACL that should deny it. The VACL is applied correctly, and the ACL entries are properly configured. What is the most likely reason for this behavior?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VACLs only filter traffic between VLANs, not within the same VLAN.
VLAN ACLs (VACLs) operate at Layer 2 and filter traffic entering or leaving a VLAN, but they only apply to traffic that crosses VLAN boundaries (i.e., inter-VLAN routing). Traffic between two ports within the same VLAN is bridged at Layer 2 and never traverses the VACL enforcement point, so the ACL entries have no effect on intra-VLAN communication. This is a fundamental design limitation of VACLs on Cisco Nexus switches.
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.
✓
VACLs only filter traffic between VLANs, not within the same VLAN.
Why this is correct
VACLs filter inter-VLAN traffic; intra-VLAN traffic is not affected.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The VACL requires Layer 3 inspection to be enabled.
Why it's wrong here
VACLs work at Layer 2 and do not require L3 inspection.
✗
The switch does not support hardware VACL processing.
Why it's wrong here
Nexus 9000 supports hardware VACL processing.
✗
Spanning-tree is bypassing the VACL for PortFast ports.
Why it's wrong here
Spanning-tree does not bypass VACLs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that VACLs filter all traffic within a VLAN, when in fact they only apply to traffic crossing VLAN boundaries, leading candidates to overlook the intra-VLAN limitation.
Detailed technical explanation
How to think about this question
VACLs are implemented using a separate TCAM region (e.g., 'vacl' region) on Nexus switches, and they are evaluated at the VLAN ingress or egress boundary. Traffic that remains within the same VLAN is switched in hardware without consulting the VACL table, as the forwarding decision is based solely on the MAC address table. In real-world scenarios, this means that to restrict intra-VLAN traffic, you must use a private VLAN (PVLAN) or a port-based ACL (PACL) applied directly to the switchport.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: VACLs only filter traffic between VLANs, not within the same VLAN. — VLAN ACLs (VACLs) operate at Layer 2 and filter traffic entering or leaving a VLAN, but they only apply to traffic that crosses VLAN boundaries (i.e., inter-VLAN routing). Traffic between two ports within the same VLAN is bridged at Layer 2 and never traverses the VACL enforcement point, so the ACL entries have no effect on intra-VLAN communication. This is a fundamental design limitation of VACLs on Cisco Nexus switches.
What should I do if I get this 350-601 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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