Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A network engineer needs to add a new switch to an existing network. The switch must be configured to support VLANs and trunking. The engineer connects the switch to the existing network via a trunk port. After configuration, the VLANs on the new switch are not receiving traffic from the core network. The core switch shows the trunk is up but no VLANs are allowed. What 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 native VLAN mismatch
A native VLAN mismatch can cause traffic issues, but typically the trunk would still forward other VLAN traffic. The trunk being up indicates the native VLAN mismatch is not the primary issue here.
B
Distractor review
The trunk encapsulation is not set to 802.1Q
If the encapsulation is not 802.1Q, the trunk would likely fail to negotiate or be down. Since the trunk is up, encapsulation is likely correct.
C
Best answer
The allowed VLAN list on the trunk does not include the desired VLANs
The allowed VLAN list explicitly controls which VLANs are permitted on the trunk. If the desired VLANs are not in the allowed list, their traffic will be dropped.
D
Distractor review
The switch port mode is set to access
If the port were in access mode, it would not form a trunk. The trunk being up indicates the port is configured as a trunk.
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 allowed VLAN list on the trunk does not include the desired VLANs — When a trunk port is up but no VLAN traffic passes, the allowed VLAN list on the trunk is often the culprit. The core switch trunk likely has a default allow list that excludes the desired VLANs. Native VLAN mismatch or encapsulation issues usually cause the trunk to not come up properly, but the trunk is up here. Access port mode would prevent trunking.
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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