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300-410 Practice Question: An engineer configures SPAN on a Cisco switch to…
An engineer configures SPAN on a Cisco switch to monitor both ingress and egress traffic on a trunk port. The monitor session shows only egress traffic, not ingress. What is the most likely explanation?
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 trunk port is configured with 'switchport trunk allowed vlan' that excludes the VLANs carrying the ingress traffic.
When monitoring a trunk port with SPAN, the source can be specified as both ingress and egress. However, if the trunk port is configured with 'switchport trunk allowed vlan' to prune certain VLANs, ingress traffic on pruned VLANs is not forwarded to the SPAN destination. Additionally, SPAN may not capture ingress traffic on the native VLAN if the native VLAN is not explicitly included.
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 trunk port is configured with 'switchport trunk allowed vlan' that excludes the VLANs carrying the ingress traffic.
Why this is correct
SPAN only captures traffic on VLANs that are allowed on the trunk; pruned VLANs are not monitored.
- ✗
The SPAN session is configured with 'monitor session 1 source interface gigabitethernet0/1 rx', missing the 'tx' keyword.
Why it's wrong here
The engineer configured both directions, so this is not the issue.
- ✗
The switch has 'spanning-tree portfast' enabled on the trunk, disabling ingress monitoring.
Why it's wrong here
Portfast does not affect SPAN functionality.
- ✗
The SPAN destination port is in the same VLAN as the ingress traffic, causing a loop.
Why it's wrong here
SPAN destination ports are not part of the source VLAN; loops are not relevant.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 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 300-410 exam.