CCNA Switching and Network Access Practice Question
Exhibit
SW1 Gi0/1 trunk allowed vlan 10,20 SW2 Gi0/1 trunk allowed vlan 10,20 Both switches have VLAN 30 configured and access ports assigned correctly.
Exhibit: Users on SW2 in VLAN 30 can reach local devices but not hosts in VLAN 30 on SW1. What is the most likely reason?
⚠ Common exam trap
Ensure you verify trunk configurations when VLAN traffic is not passing between switches, even if VLANs are correctly configured locally.
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
✓
VLAN 30 is not allowed on the trunk
The trunk is allowing only VLANs 10 and 20. Even though both switches have VLAN 30 defined locally, VLAN 30 traffic cannot cross the trunk unless that VLAN is allowed on the link. Option A is incorrect because the native VLAN (default 1) does not affect tagged VLAN 30 traffic, and native VLAN mismatch causes different issues. Option C is incorrect because VTP is used for VLAN database synchronization, not for forwarding traffic over a trunk; switches do not need to be VTP servers to pass VLAN traffic. Option D is incorrect because spanning tree only blocks redundant paths to prevent loops, not all user VLANs by default.
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 native VLAN is 1 on both sides
Why it's wrong here
The native VLAN applies only to untagged frames on a trunk, and both sides having native VLAN 1 is a consistent, default configuration that would not block tagged VLAN 30 traffic. VLAN 30 frames would typically be sent with an 802.1Q tag, so the native VLAN setting has no bearing on their forwarding. If a native VLAN mismatch existed, it would affect untagged management traffic, not the tagged user VLAN that already has local connectivity.
When this WOULD be correct
In a scenario where the question specifies that a trunk link is misconfigured with a native VLAN that is not set to match on both ends, leading to VLAN traffic being dropped, this option could be correct. For example, if the question states that VLAN 30 is configured but traffic is not passing due to mismatched native VLAN settings, this would be the right answer.
- ✓
VLAN 30 is not allowed on the trunk
Why this is correct
Inter-switch traffic for a VLAN requires that VLAN to be present in the trunk's allowed list on both ends. When VLAN 30 is omitted or 'pruned' from that list, frames are discarded at the trunk port, so SW2's local clients can communicate within their broadcast domain but cannot reach devices beyond the switch. The command 'show interfaces trunk' would reveal that VLAN 30 is not in the allowed VLAN list, confirming the filter is the cause.
- ✗
SW2 must run VTP server mode
Why it's wrong here
VTP mode controls VLAN database advertisement, not the per-interface permitted VLAN list. SW2 could be a VTP server or client and still drop VLAN 30 on a trunk if the trunk's allowed list excludes it. Since local hosts in VLAN 30 can already communicate, the VLAN exists; the missing remote reachability points to trunk filtering, not VTP. Changing VTP mode would not alter the trunk's configured allowed VLANs.
When this WOULD be correct
In a scenario where a question asks about the necessity of VTP server mode for VLAN propagation across multiple switches, and it specifies that VLANs must be synchronized across the network, this option would be correct. For example, if the question states that SW1 and SW2 are part of a larger VTP domain and VLAN configurations must be consistent across all switches.
- ✗
Spanning tree blocks all user VLANs by default
Why it's wrong here
Spanning Tree Protocol places redundant interfaces into a blocking state to prevent loops, but it does not block all user VLANs by default; normal forwarding ports remain active for every allowed VLAN. If STP were blocking VLAN 30, local devices on SW2 would also fail to communicate because their access ports would be in a blocking or disabled state. Since local reachability works and the failure is specific to remote destinations, a trunk-level VLAN filtering issue—not STP—is the correct explanation.
When this WOULD be correct
In a different scenario where a question states that all VLANs are configured correctly but a specific VLAN is being blocked due to STP configuration issues, option D would be correct. For example, if a question describes a network with multiple VLANs and asks why users cannot communicate due to STP settings, option D would apply.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓VLAN 30 is not allowed on the trunkCorrect answer▾
Why this is correct
Inter-switch traffic for a VLAN requires that VLAN to be present in the trunk's allowed list on both ends. When VLAN 30 is omitted or 'pruned' from that list, frames are discarded at the trunk port, so SW2's local clients can communicate within their broadcast domain but cannot reach devices beyond the switch. The command 'show interfaces trunk' would reveal that VLAN 30 is not in the allowed VLAN list, confirming the filter is the cause.
✗The trunk native VLAN is 1 on both sidesWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because the native VLAN being set to 1 does not prevent VLAN 30 traffic from being transmitted across the trunk link. The issue lies in VLAN 30 not being allowed on the trunk, which is not addressed by the native VLAN setting.
★ When this WOULD be the correct answer
In a scenario where the question specifies that a trunk link is misconfigured with a native VLAN that is not set to match on both ends, leading to VLAN traffic being dropped, this option could be correct. For example, if the question states that VLAN 30 is configured but traffic is not passing due to mismatched native VLAN settings, this would be the right answer.
Why candidates choose this
Candidates may choose this option due to a common misconception that native VLAN configurations directly affect all VLAN traffic, leading them to overlook the specific trunk configuration details that are crucial in this scenario.
✗SW2 must run VTP server modeWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because VTP server mode is not required for VLANs to communicate across switches; VLAN configuration can be done independently on each switch. The issue in the question is related to trunking and VLAN allowance, not VTP mode.
★ When this WOULD be the correct answer
In a scenario where a question asks about the necessity of VTP server mode for VLAN propagation across multiple switches, and it specifies that VLANs must be synchronized across the network, this option would be correct. For example, if the question states that SW1 and SW2 are part of a larger VTP domain and VLAN configurations must be consistent across all switches.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of VTP's role in VLAN management and a belief that VTP server mode is essential for VLAN communication, leading them to overlook the actual trunking issue presented in the question.
✗Spanning tree blocks all user VLANs by defaultWrong answer — click to see why▾
Why this is wrong here
Spanning Tree Protocol (STP) does not block all user VLANs by default; it only blocks specific ports to prevent loops. In this case, the issue is related to VLAN 30 not being allowed on the trunk, not STP blocking the VLAN.
★ When this WOULD be the correct answer
In a different scenario where a question states that all VLANs are configured correctly but a specific VLAN is being blocked due to STP configuration issues, option D would be correct. For example, if a question describes a network with multiple VLANs and asks why users cannot communicate due to STP settings, option D would apply.
Why candidates choose this
Candidates may choose this option due to a general understanding of STP and its role in preventing loops, mistakenly believing that it applies to all VLANs without considering the specific context of VLAN configuration and trunk settings.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
VLAN mismatch
A VLAN mismatch occurs when two connected network devices are configured with different VLAN assignments on the same link, causing traffic to be dropped or misrouted.
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.