Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A network administrator connects two switches with a trunk link that is configured to allow all VLANs. Workstations in VLAN 10 can communicate across the switches, but workstations in VLAN 20 cannot. Both VLANs are configured on the first switch. What is the most likely cause of the issue?
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 is mismatched on the two switches.
A native VLAN mismatch would cause issues for untagged frames, but would affect all VLANs if configured incorrectly, not just VLAN 20. This is not the most likely cause.
B
Best answer
VLAN 20 is not created on the second switch.
Correct. If VLAN 20 does not exist on the second switch, it will discard frames received on the trunk tagged with VLAN 20. Creating the VLAN on both switches is essential for inter-switch communication.
C
Distractor review
The trunk uses ISL instead of 802.1Q.
Both ISL and 802.1Q work with multiple VLANs. If both switches support ISL and it is configured correctly, this would not cause a selective problem for VLAN 20.
D
Distractor review
The default gateway is missing for VLAN 20.
A default gateway is required for inter-VLAN routing, not for communication within the same VLAN across switches. Since VLAN 20 is a single broadcast domain, a gateway is not needed for intra-VLAN traffic.
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: VLAN 20 is not created on the second switch. — For communication between devices in the same VLAN across switches, the VLAN must be present on both switches. If VLAN 20 is not created (or is deleted/shutdown) on the second switch, frames tagged for VLAN 20 arriving via the trunk will be dropped because the switch does not have the VLAN in its database. Trunk configuration issues like native VLAN mismatch or encapsulation mismatch typically affect all VLANs, not a specific one.
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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