The answer is that the SPAN source does not include that VLAN. This is because a Switched Port Analyzer (SPAN) port only copies traffic from explicitly configured source interfaces or VLANs to the destination port; if a specific VLAN is not listed in the `monitor session` command using the `vlan` keyword, its traffic will never reach the IDS. On the Cisco CyberOps Associate 200-201 exam, this question tests your understanding of SPAN configuration fundamentals, often appearing as a trap where candidates assume a SPAN port automatically mirrors all VLAN traffic. A common mistake is thinking that enabling SPAN on a trunk port captures all VLANs, but the source must be defined per VLAN. Remember the mnemonic: “If it’s not sourced, it’s not sourced”—always verify the `vlan` keyword in the SPAN configuration to ensure the IDS receives the desired traffic.
200-201 Security Monitoring Practice Question
This 200-201 practice question tests your understanding of security monitoring. 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.
A network administrator has configured a SPAN port to send traffic to an intrusion detection system (IDS). However, the IDS is not seeing traffic from a specific VLAN. What is the most likely cause?
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
✓
The SPAN source does not include that VLAN.
A SPAN (Switched Port Analyzer) port copies traffic from specified source interfaces or VLANs to a destination port. If the IDS is not seeing traffic from a specific VLAN, the most likely cause is that the SPAN configuration does not include that VLAN as a source. The administrator must explicitly specify the VLAN(s) to monitor using the `monitor session` command with the `vlan` keyword; otherwise, traffic from that VLAN will not be forwarded to the IDS.
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 SPAN source does not include that VLAN.
Why this is correct
If the VLAN is not in the SPAN source list, its traffic is not monitored.
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 IDS interface is set to promiscuous mode.
Why it's wrong here
Promiscuous mode is required for IDS to capture traffic, not a cause of missing traffic.
✗
The SPAN destination port is in trunk mode.
Why it's wrong here
SPAN destination ports are usually access ports; trunk mode could cause issues but is not the most likely.
✗
The IDS is in inline mode.
Why it's wrong here
IDS is passive; inline mode is for IPS, not typically used with SPAN.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that SPAN automatically mirrors all VLANs on a trunk port, when in fact the administrator must explicitly specify which VLANs to monitor using the `vlan` keyword in the SPAN configuration.
Detailed technical explanation
How to think about this question
Under the hood, SPAN uses a local mirroring mechanism where the switch copies frames from the source VLAN's broadcast domain to the destination port. The `monitor session 1 source vlan X` command creates a copy of all traffic in VLAN X, but if VLAN Y is not listed, no frames from VLAN Y are mirrored. A subtle behavior is that SPAN can also filter by VLAN on a trunk source using the `vlan` keyword, but if omitted, only the native VLAN is mirrored by default. In real-world scenarios, misconfigured SPAN VLAN filters are a common cause of missing traffic in network monitoring tools like IDS/IPS.
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 Monitoring — This question tests Security Monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The SPAN source does not include that VLAN. — A SPAN (Switched Port Analyzer) port copies traffic from specified source interfaces or VLANs to a destination port. If the IDS is not seeing traffic from a specific VLAN, the most likely cause is that the SPAN configuration does not include that VLAN as a source. The administrator must explicitly specify the VLAN(s) to monitor using the `monitor session` command with the `vlan` keyword; otherwise, traffic from that VLAN will not be forwarded to the IDS.
What should I do if I get this 200-201 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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