Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A network administrator connects a new access switch to the core switch via a trunk port. Both switches have the same VLAN database, and the trunk is configured to allow all VLANs. However, hosts on VLAN 10 connected to the new access switch cannot communicate with hosts on VLAN 10 on the core switch. The administrator verifies that the access ports for VLAN 10 are correctly configured and that the trunk link status is up/up. Which of the following is the most likely cause?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
The trunk port is in an err-disabled state.
The trunk status is up/up, so it is not err-disabled. An err-disabled port would show as down.
B
Best answer
The native VLAN on the trunk port is different on the two switches.
A native VLAN mismatch can cause untagged frames to be placed into different VLANs on each switch. This can prevent communication even if the allowed VLAN list is correct. The administrator should verify that the native VLAN is the same on both ends.
C
Distractor review
The switchport mode is not set to trunk on one side.
If the trunk link is up/up, both sides are likely configured as trunk ports. The question states the trunk is configured, so this is not the issue.
D
Distractor review
The spanning-tree protocol is blocking VLAN 10 on the trunk.
Spanning tree can block specific VLANs if there is a loop, but for a simple two-switch topology this is unlikely. Moreover, the symptom is that hosts on the same VLAN cannot communicate, which is more indicative of a native VLAN issue.
Common exam trap
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.
Technical deep dive
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A network engineer needs to connect two switches located 400 meters apart. The cable run includes high electromagnetic interference from nearby machinery. The engineer decides to use fiber optic cabling. Which transceiver type and fiber combination should be used to ensure the link reaches 400 meters while remaining cost-effective?
Question 2
A network engineer is designing a new switched network and needs to ensure that broadcast traffic from one department does not reach another department's workstations. The engineer plans to use VLANs. Which of the following must be configured on the switches to isolate broadcast domains as intended?
Question 3
A security engineer is configuring a site-to-site VPN between two branch offices. The requirement is to encrypt all traffic between the two networks using IPsec. Which IPsec mode should be used to encrypt the entire IP packet including the original header?
Question 4
A network administrator is connecting two switches to increase bandwidth and provide redundancy. Which technology should be used to combine multiple physical links into a single logical link?
Question 5
A network administrator is experiencing issues where unauthorized devices are offering IP addresses to clients, causing connectivity problems. Which security feature should be enabled on switches to prevent this?
Question 6
A network administrator is troubleshooting a connectivity issue and suspects the problem is related to the physical cabling. At which layer of the OSI model should the administrator begin their investigation?
FAQ
Questions learners often ask
What does this N10-009 question test?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: The native VLAN on the trunk port is different on the two switches. — A common trunking issue is a native VLAN mismatch. If the native VLAN on one end differs from the other, untagged frames (like those sent by many devices) may be placed into different VLANs, causing communication failures. In this scenario, even though the allowed VLAN list includes VLAN 10, if the native VLAN is different, management traffic and possibly other frames could be misclassified, disrupting connectivity.
What should I do if I get this N10-009 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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