The answer is that the ERSPAN session must be configured with the 'vrf' keyword under the destination to use VRF B. By default, ERSPAN encapsulates mirrored traffic and routes it using the global routing table, regardless of which VRF the source interface belongs to. Since the collector at 192.168.1.100 resides in VRF B and the global table lacks a route to it, the encapsulated packets are dropped—route-leaking between VRFs does not affect ERSPAN’s forwarding decision. This question tests your understanding of how ERSPAN interacts with VRFs on the Cisco CCNP ENARSI 300-410 exam, a common trap where candidates assume the source interface’s VRF applies to the destination. The fix is to add the 'vrf B' keyword to the destination configuration. Memory tip: ERSPAN defaults to the global table—always specify the VRF when the collector lives in a non-global routing context.
300-410 SPAN, RSPAN, and ERSPAN Practice Question
This 300-410 practice question tests your understanding of span, rspan, and erspan. 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.
An engineer configures ERSPAN on Router R1 to monitor traffic from VLAN 30 to a collector at 192.168.1.100. The router has multiple VRFs: VRF A and VRF B. The source interface Gi0/0/0 is in VRF A. The collector is in VRF B. R1's configuration: monitor session 1 type erspan-source source interface Gi0/0/0 both destination erspan-id 2 ip address 192.168.1.100 origin ip address 10.0.0.1. The collector is reachable via a route in VRF B. The router has a route-leaking configuration between VRFs. The collector receives no traffic. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ERSPAN session must be configured with the 'vrf' keyword under the destination to use VRF B.
ERSPAN uses the global routing table by default to route the encapsulated packets to the destination IP. If the source interface is in a VRF, the mirrored traffic is still sent using the global routing table unless the ERSPAN session is configured with a VRF. The destination IP 192.168.1.100 is in VRF B, but the global routing table may not have a route to it. The route-leaking between VRFs does not affect the ERSPAN process because the encapsulated packet is sourced from the global routing table. The fix is to configure the ERSPAN session with the 'vrf' keyword under the destination to specify the VRF. Alternatively, the source IP must be in the same VRF as the destination. The correct root cause is that the ERSPAN session does not specify the VRF, so it uses the global table, which has no route to the collector.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 ERSPAN session must be configured with the 'vrf' keyword under the destination to use VRF B.
Why this is correct
Without the VRF keyword, ERSPAN uses the global routing table, which lacks a route to the collector in VRF B.
Related concept
Access ports place end devices into a single VLAN.
✗
The source interface is in VRF A, but the ERSPAN source IP must be in the same VRF as the destination.
Why it's wrong here
The source IP is in the global table by default; the issue is the routing table used for the destination.
✗
The route-leaking configuration is incorrect, preventing reachability between VRFs.
Why it's wrong here
Route-leaking may be correct, but ERSPAN does not use leaked routes unless the VRF is specified.
✗
The ERSPAN session ID 2 conflicts with a VRF ID.
Why it's wrong here
There is no such conflict.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 300-410 questions on switching, trunking, and access-port configuration.
SPAN, RSPAN, and ERSPAN — This question tests SPAN, RSPAN, and ERSPAN — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The ERSPAN session must be configured with the 'vrf' keyword under the destination to use VRF B. — ERSPAN uses the global routing table by default to route the encapsulated packets to the destination IP. If the source interface is in a VRF, the mirrored traffic is still sent using the global routing table unless the ERSPAN session is configured with a VRF. The destination IP 192.168.1.100 is in VRF B, but the global routing table may not have a route to it. The route-leaking between VRFs does not affect the ERSPAN process because the encapsulated packet is sourced from the global routing table. The fix is to configure the ERSPAN session with the 'vrf' keyword under the destination to specify the VRF. Alternatively, the source IP must be in the same VRF as the destination. The correct root cause is that the ERSPAN session does not specify the VRF, so it uses the global table, which has no route to the collector.
What should I do if I get this 300-410 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 300-410 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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