N10-009 Network Implementation Practice Question
A network administrator adds a new server to VLAN 20. The switch port is configured as an access port in VLAN 20, and the server has a correct static IP address in that subnet. However, the server cannot communicate with other devices in the same VLAN. The VLAN exists on the switch and other devices in VLAN 20 are working. What is the most likely cause of this issue?
⚠ Common exam trap
CompTIA often tests the distinction between access and trunk ports by presenting a scenario where a device has correct IP settings but cannot communicate within its VLAN, tempting candidates to blame routing or gateway issues when the real problem is a layer 2 VLAN mismatch caused by trunk mode on an access port.
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
✓
The switch port is configured as a trunk port instead of an access port
The scenario states the switch port is configured as an access port in VLAN 20, but the server cannot communicate with other devices in the same VLAN. If the port were actually configured as a trunk port, it would expect frames to be tagged with a VLAN ID. An untagged frame from the server would be placed into the native VLAN (typically VLAN 1), not VLAN 20, causing a mismatch. This explains why the server, despite having a correct static IP in VLAN 20's subnet, cannot reach other devices in VLAN 20.
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 switch port is configured as a trunk port instead of an access port
Why this is correct
A server typically sends standard untagged Ethernet frames, as it is generally unaware of VLAN tagging. If the switch port connected to this server is mistakenly configured as a trunk port, it will expect incoming frames to be 802.1Q tagged with a specific VLAN ID. Since the server's frames arrive untagged, the switch will not correctly associate them with VLAN 20, effectively dropping them or placing them in a default native VLAN, thereby preventing communication within VLAN 20. This misconfiguration is a very common cause of connectivity failure for end devices.
- ✗
VLAN 20 is not allowed on the trunk to the router
Why it's wrong here
If VLAN 20 is explicitly disallowed on the trunk link connecting the switch to the router, it would indeed prevent devices in VLAN 20 from communicating with devices in *other* VLANs or external networks. This is because inter-VLAN routing relies on the router receiving tagged frames for all allowed VLANs. However, this specific configuration issue would not impact communication *between* devices that are all members of VLAN 20 and connected to the same switch or switches where VLAN 20 is properly configured, as intra-VLAN communication does not traverse a router.
When this WOULD be correct
This option would be correct if the server needed to communicate with devices in a different VLAN or access the internet, and the trunk port connecting the switch to the router did not have VLAN 20 allowed, preventing inter-VLAN routing.
- ✗
The server does not have a default gateway configured
Why it's wrong here
A default gateway is a crucial IP address that enables a device to send traffic to destinations outside its immediate local IP subnet, typically to other VLANs or the internet. However, communication between devices residing within the *same* VLAN and IP subnet occurs at Layer 2 and does not require a default gateway. Therefore, the absence of a default gateway would not prevent the new server from communicating with other devices that are also members of VLAN 20.
When this WOULD be correct
A server in VLAN 20 cannot communicate with devices in a different VLAN or subnet, and the question specifies that inter-VLAN routing is required. In that case, a missing default gateway would prevent traffic from leaving the local subnet.
- ✗
The port is administratively down
Why it's wrong here
If a switch port is administratively down, it signifies that the port has been manually disabled by a network administrator using a command like "shutdown." In such a state, the port would not establish a link or pass any traffic whatsoever, resulting in a complete lack of physical layer connectivity for the server. The question implies the server is connected but merely unable to communicate within VLAN 20, which suggests the port is physically up but logically misconfigured, not entirely disabled.
When this WOULD be correct
A network administrator reports that a newly connected device has no network connectivity at all, and the switch port shows 'administratively down' in the interface status. The most likely cause is that the port was manually disabled (shutdown) and needs to be enabled with 'no shutdown'.
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 N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓The switch port is configured as a trunk port instead of an access portCorrect answer▾
Why this is correct
A server typically sends standard untagged Ethernet frames, as it is generally unaware of VLAN tagging. If the switch port connected to this server is mistakenly configured as a trunk port, it will expect incoming frames to be 802.1Q tagged with a specific VLAN ID. Since the server's frames arrive untagged, the switch will not correctly associate them with VLAN 20, effectively dropping them or placing them in a default native VLAN, thereby preventing communication within VLAN 20. This misconfiguration is a very common cause of connectivity failure for end devices.
✗VLAN 20 is not allowed on the trunk to the routerWrong answer — click to see why▾
Why this is wrong here
The question states the server cannot communicate with other devices in the same VLAN. A trunk to a router is irrelevant for intra-VLAN communication, which occurs at Layer 2 within the switch. The issue is local to the switch port configuration.
★ When this WOULD be the correct answer
This option would be correct if the server needed to communicate with devices in a different VLAN or access the internet, and the trunk port connecting the switch to the router did not have VLAN 20 allowed, preventing inter-VLAN routing.
Why candidates choose this
Candidates may confuse intra-VLAN communication with inter-VLAN routing, assuming that a missing VLAN on a trunk would affect all communication, including local traffic within the same VLAN.
✗The server does not have a default gateway configuredWrong answer — click to see why▾
Why this is wrong here
The server has a correct static IP address in the same subnet, and other devices in VLAN 20 are working, so communication within the VLAN does not require a default gateway. The issue is at Layer 2, not Layer 3.
★ When this WOULD be the correct answer
A server in VLAN 20 cannot communicate with devices in a different VLAN or subnet, and the question specifies that inter-VLAN routing is required. In that case, a missing default gateway would prevent traffic from leaving the local subnet.
Why candidates choose this
Candidates often associate network connectivity issues with missing default gateways, but they overlook that intra-VLAN communication does not need a gateway.
✗The port is administratively downWrong answer — click to see why▾
Why this is wrong here
The question states the server cannot communicate with other devices in the same VLAN, but other devices in VLAN 20 are working. If the port were administratively down, no devices on that port would work, and the server would not have link. The issue is specific to this server, not a port status problem.
★ When this WOULD be the correct answer
A network administrator reports that a newly connected device has no network connectivity at all, and the switch port shows 'administratively down' in the interface status. The most likely cause is that the port was manually disabled (shutdown) and needs to be enabled with 'no shutdown'.
Why candidates choose this
Candidates may think 'administratively down' is a common misconfiguration, but the question's symptom (server can't communicate with same VLAN) points to a VLAN mismatch, not a disabled port. They overlook that other devices in VLAN 20 work, ruling out a global VLAN issue.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Related to this question
Learn chapter
Physical Network Infrastructure
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
Key term
IP address
An IP address is a unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA 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 N10-009 exam.