Quick Answer
The answer is that VLAN 20 has not been created on the switch. This is the most likely cause of a VLAN not created connectivity issue because an access port assigned to a non-existent VLAN cannot forward traffic at Layer 2; the switch has no VLAN database entry to map the frames to, so they are effectively dropped even though the physical interface shows as up/up. On the CCNA 200-301 v2 exam, this scenario tests your understanding that a port’s link state is independent of the VLAN’s existence—a common trap where candidates assume “up/up” means full connectivity. Remember that creating a VLAN is a separate step from assigning it to a port; a missing VLAN breaks the logical path to the default gateway. Memory tip: “No VLAN, no LAN—up/up means nothing if the VLAN is missing.”
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: a switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly.. 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.
A switchport is configured as an access port for VLAN 20, but users connected to it cannot reach the default gateway. The switch shows the interface as up/up. Which switch misconfiguration is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The access port is missing a speed command
Why wrong: Distractor.
VLAN 20 has not been created on the switch
Correct choice.
The switch has not enabled VTP transparent mode
Why wrong: Distractor.
The port should use DTP desirable mode
Why wrong: Distractor.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
VLAN 20 has not been created on the switch
If the access port is assigned to VLAN 20 but VLAN 20 does not exist in the VLAN database, traffic is not placed into a usable VLAN and hosts lose connectivity. The port can still appear physically up while forwarding fails at Layer 2.
Key principle: A switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The access port is missing a speed command
Why it's wrong here
Distractor.
When this WOULD be correct
In a different scenario, if a question specified that a switchport is operational but experiencing performance issues or intermittent connectivity, and the configuration lacks a speed command, then this option could be correct as speed mismatches can cause such problems.
VLAN 20 has not been created on the switch
Why this is correct
Correct choice.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
A switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly.
The switch has not enabled VTP transparent mode
Why it's wrong here
Distractor.
When this WOULD be correct
In a scenario where a question asks about VLAN propagation issues in a network using VTP, and the context specifies that VLANs must be created on a VTP server for clients to access them, this option would be correct if the switch was not configured to propagate VLAN information properly.
The port should use DTP desirable mode
Why it's wrong here
Distractor.
When this WOULD be correct
In a scenario where the question specifies that the switchport is intended to be a trunk port and needs to negotiate trunking with a connected device, selecting D would be correct if the port was incorrectly set to access mode instead of trunk mode using DTP.
Option-by-option analysis
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.
Why this is correct
Correct choice.
Why this is wrong here
The speed command is used for setting the interface speed (e.g., 10/100/1000 Mbps) and does not affect VLAN membership or layer 3 reachability. A missing speed command would not prevent users from reaching the default gateway as long as the interface is up/up.
★ When this WOULD be the correct answer
In a different scenario, if a question specified that a switchport is operational but experiencing performance issues or intermittent connectivity, and the configuration lacks a speed command, then this option could be correct as speed mismatches can cause such problems.
Why candidates choose this
Students might think that a missing speed command could cause connectivity issues, but speed mismatches typically cause the interface to be down/down, not up/up. Since the interface is up/up, speed is not the issue.
Why this is wrong here
VTP transparent mode is a VTP (VLAN Trunking Protocol) setting that allows a switch to forward VTP advertisements without participating in VLAN database synchronization. It is not required for basic VLAN operation; VLANs can be created locally regardless of VTP mode. The issue here is that VLAN 20 does not exist, not that VTP mode is incorrect.
★ When this WOULD be the correct answer
In a scenario where a question asks about VLAN propagation issues in a network using VTP, and the context specifies that VLANs must be created on a VTP server for clients to access them, this option would be correct if the switch was not configured to propagate VLAN information properly.
Why candidates choose this
Students may confuse VTP transparent mode with the requirement for VLANs to be propagated via VTP. However, in a network without VTP or with VTP transparent mode, VLANs must be created manually. The absence of VTP transparent mode does not prevent VLAN creation.
Why this is wrong here
DTP (Dynamic Trunking Protocol) desirable mode is used to negotiate trunking on a port. An access port should not use DTP desirable mode; it should be configured as an access port with 'switchport mode access'. Using DTP desirable could cause the port to become a trunk, which would not allow the VLAN 20 traffic to be properly handled as access traffic.
★ When this WOULD be the correct answer
In a scenario where the question specifies that the switchport is intended to be a trunk port and needs to negotiate trunking with a connected device, selecting D would be correct if the port was incorrectly set to access mode instead of trunk mode using DTP.
Why candidates choose this
Students might think that DTP desirable helps with VLAN negotiation, but it is for trunking, not access VLAN assignment. The correct configuration for an access port is to set it to access mode, not to use DTP.
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?”
Common exam traps
A common exam trap is assuming that an interface showing up/up means the port is fully functional and correctly forwarding traffic. Candidates may overlook the necessity of creating the VLAN in the switch’s VLAN database. Without VLAN 20 existing, the switch cannot forward traffic for that VLAN, even though the physical link is active. This leads to confusion because the interface status does not reflect VLAN misconfiguration, causing users to lose connectivity to the default gateway despite the port appearing operational.
Detailed technical explanation
VLANs (Virtual Local Area Networks) segment a physical switch into multiple logical broadcast domains, allowing traffic separation and improved network management. Each VLAN is identified by a VLAN ID and must be explicitly created in the switch's VLAN database. Access ports are configured to assign all incoming untagged frames to a specific VLAN, ensuring hosts connected to these ports communicate within that VLAN's broadcast domain. When a switchport is configured as an access port for VLAN 20, the switch expects VLAN 20 to exist in its VLAN database. If VLAN 20 has not been created, the switch cannot associate the port's traffic with a valid VLAN. Although the physical interface may show as up/up, indicating the link is operational, the Layer 2 forwarding process fails because the VLAN context is missing. This results in hosts connected to that port being unable to reach devices outside their local segment, such as the default gateway. This scenario is a common exam trap because the interface status can mislead candidates into thinking the port is fully operational. However, VLAN configuration is critical for Layer 2 forwarding. The practical impact is that traffic is dropped silently, causing connectivity issues. Network engineers must verify VLAN existence and proper assignment to access ports to ensure correct Layer 2 communication and avoid such silent failures.
Key takeaway
A switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly.
Real-world example
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.
What to study next
Review a switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Switching and Network Access — This question tests Switching and Network Access — A switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly..
The correct answer is: VLAN 20 has not been created on the switch — If the access port is assigned to VLAN 20 but VLAN 20 does not exist in the VLAN database, traffic is not placed into a usable VLAN and hosts lose connectivity. The port can still appear physically up while forwarding fails at Layer 2.
Review a switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly., then practise related 200-301 questions on the same topic to reinforce the concept.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
A switchport configured as an access port assigns all incoming traffic to a single VLAN, which must exist in the VLAN database to forward traffic correctly.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A PC connected to SW1 cannot reach the default gateway. The access port is assigned to VLAN 20, and the switch output shows that VLAN 20 is inactive. What is the most likely cause?
hardWhy B: The port is operationally up, but VLAN 20 is listed as inactive because that VLAN does not exist in the VLAN database. An access port assigned to a missing VLAN will not carry normal user traffic for that VLAN.
Last reviewed: May 17, 2026
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