20+ practice questions focused on SPAN and RSPAN — one of the most tested topics on the ENCOR 350-401 exam. Each question includes a detailed explanation so you learn why the right answer is correct.
Start SPAN and RSPAN PracticeA network engineer is troubleshooting a performance issue between two hosts connected to a Cisco Catalyst 3850 switch. The engineer wants to capture all traffic sent and received by Host A (Gi1/0/1) and send it to a monitoring station connected to Gi1/0/24. The engineer configures 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 destination interface Gi1/0/24'. However, the monitoring station receives only traffic sent by Host A, not traffic received. What is the most likely cause?
Explanation: The 'both' keyword should capture both directions, but on some platforms, the destination port must be explicitly configured to allow ingress traffic for received traffic to be copied. The correct answer is that the destination port is not configured with 'monitor session 1 destination interface Gi1/0/24 ingress untagged' or similar, but the question focuses on a common misconfiguration: the destination port is in the same VLAN as the source, causing loops or filtering. Actually, the most common cause is that the source interface is configured as 'both' but the switch does not support egress SPAN on that interface without additional configuration. However, the best answer here is that the source interface is an access port and the destination port is in a different VLAN, and the SPAN session does not copy traffic from the source VLAN. But the scenario says both hosts are in the same VLAN. The correct answer is that the destination port is not configured to allow the SPAN traffic to be sent out; actually, the issue is that the destination port is in the same VLAN as the source, and the switch may drop the copied frames due to loop prevention. The most accurate answer: The engineer must ensure the destination port is not in the same VLAN as the source, or use a remote SPAN (RSPAN) VLAN. But the question asks for the cause. The cause is that the destination port is in the same VLAN as the source, and the switch's loop detection drops the copied frames. So the correct answer is that the destination port is in the same VLAN as the source interface, causing the switch to drop the replicated traffic.
A network engineer needs to monitor traffic between two VLANs on a Cisco Catalyst 9300 switch. The engineer wants to capture all packets that traverse the switch between VLAN 10 and VLAN 20. The monitoring station is connected to port Gi1/0/24. Which configuration should the engineer use to capture this inter-VLAN traffic?
Explanation: Inter-VLAN traffic is routed by the switch's Layer 3 engine. To capture it, the engineer must use a SPAN session that sources from the VLANs themselves (VLAN-based SPAN) or from the SVI. The correct answer is to configure a SPAN session with source VLANs 10 and 20, and destination interface Gi1/0/24. This captures all traffic entering or leaving those VLANs, including routed traffic. Option A is incorrect because interface SPAN would only capture traffic on that specific port, not all inter-VLAN traffic. Option C is incorrect because RSPAN is for remote monitoring, not needed here. Option D is incorrect because ERSPAN is for encapsulated remote SPAN over IP, not needed.
An engineer is configuring RSPAN to monitor traffic from multiple switches in a data center. The monitoring station is connected to a central switch. The engineer has configured an RSPAN VLAN (VLAN 999) on all switches and set up the source sessions on the remote switches. However, the monitoring station receives no traffic. On the central switch, the engineer verifies that the RSPAN VLAN is active and that the destination session is configured. What is a likely missing configuration?
Explanation: For RSPAN to work, the RSPAN VLAN must be allowed on all trunk links between the source switches and the destination switch. If the trunk ports do not have the RSPAN VLAN in their allowed list, the traffic will be dropped. Also, the RSPAN VLAN must not be pruned by VTP. The correct answer is that the trunk ports between the switches are not configured to allow the RSPAN VLAN. Option B is incorrect because the destination session is already configured. Option C is incorrect because the source session is already configured. Option D is incorrect because the RSPAN VLAN is active.
A network engineer is using a Cisco Catalyst 3850 switch to monitor traffic from a server connected to port Gi1/0/1. The monitoring station is on port Gi1/0/24. The engineer configures 'monitor session 1 source interface Gi1/0/1 both' and 'monitor session 1 destination interface Gi1/0/24'. The monitoring station receives traffic, but the engineer notices that the switch CPU utilization is high. What is the most likely cause of the high CPU?
Explanation: SPAN can cause high CPU if the destination port is not configured with 'ingress' or if the switch is overloaded. However, a common cause is that the destination port is configured to also forward traffic normally (i.e., it is not a dedicated SPAN destination). But the question says the monitoring station receives traffic, so the destination port is working. High CPU can occur if the SPAN session is configured to capture from a large number of sources or if the switch is processing many packets. The most likely cause here is that the destination port is not configured with 'switchport nonegotiate' or is in a VLAN that causes the switch to process the copied frames as normal traffic, leading to high CPU. But the best answer: The destination port should be configured as a SPAN destination only, and if it is also a member of a VLAN, the switch may try to switch the copied frames, causing high CPU. The correct answer is that the destination port is not configured as a SPAN destination-only port; it is still a member of a VLAN, causing the switch to process the copied frames as normal traffic.
A network engineer needs to monitor traffic from a specific VLAN (VLAN 100) on a Cisco Catalyst 9300 switch and send the mirrored traffic to a monitoring station on a different switch across a routed network. The engineer decides to use ERSPAN. Which configuration is required on the source switch?
Explanation: ERSPAN encapsulates mirrored traffic in GRE and sends it over IP. On the source switch, the engineer must configure an ERSPAN source session that specifies the source VLAN and the destination IP address of the monitoring station or the destination switch. The correct answer is to configure 'monitor session 1 type erspan-source' and then specify the source VLAN and the destination IP. Option B is incorrect because that is for local SPAN. Option C is incorrect because that is for RSPAN. Option D is incorrect because that is for local SPAN with a VLAN source.
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Practice all SPAN and RSPAN questions1. Baseline your knowledge
Start with 10 questions to gauge your current understanding of SPAN and RSPAN. This tells you whether you need a concept refresher or just practice.
2. Review every explanation
For each question — right or wrong — read the full explanation. Understanding why an answer is correct is more valuable than knowing the answer itself.
3. Focus on exam traps
SPAN and RSPAN questions on the 350-401 frequently use trap wording. Look for subtle differences in answers that test your precision, not just general knowledge.
4. Reach 80% consistently
Do repeated sessions until you score 80%+ three times in a row. Then move to mixed-mode practice to test cross-topic recall under realistic conditions.
The exact number varies per candidate. SPAN and RSPAN is tested as part of the ENCOR 350-401 blueprint. Practicing with targeted SPAN and RSPAN questions ensures you can handle any format or difficulty that appears.
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