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300-410 Practice Question: An engineer configures ERSPAN on a Cisco router…
An engineer configures ERSPAN on a Cisco router to monitor traffic from a tunnel interface. The mirrored traffic shows the tunnel's inner IP headers, but the outer encapsulation is missing. What is the most likely cause?
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
✓
ERSPAN on a tunnel interface captures the inner IP packet, not the encapsulated GRE/IPsec packet.
When monitoring a tunnel interface with ERSPAN, the router captures the traffic at the point where it enters the tunnel (before encapsulation) or exits (after decapsulation). To capture the encapsulated packets, the source must be the physical egress interface, not the tunnel interface. By default, ERSPAN on a tunnel interface shows the inner packet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ERSPAN on a tunnel interface captures the inner IP packet, not the encapsulated GRE/IPsec packet.
Why this is correct
The tunnel interface processes the inner packet; the outer encapsulation is added later on the physical interface.
- ✗
The ERSPAN session is configured with 'erspan-type' that strips the outer header.
Why it's wrong here
There is no such configuration option.
- ✗
The collector is not configured to decode GRE headers.
Why it's wrong here
The issue is on the source, not the collector.
- ✗
The tunnel interface is in a VRF, causing the outer header to be removed.
Why it's wrong here
VRF does not affect encapsulation visibility.
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JA
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.