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200-201 Practice Question: A network administrator has configured a SPAN…
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?
⚠ Common exam trap
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.
Answer choices
Why each option matters
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.
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.
- ✗
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-201 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 200-201 exam.