Question 1easymultiple choice
Full question →easymultiple choiceObjective-mapped
A network administrator configures a trunk link between two switches. The link is up, but no traffic from any VLAN is passed between the switches. The administrator verifies that the trunk port is configured correctly on both switches with 'switchport mode trunk' and allowed VLANs. 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 native VLAN is different on each switch
While a native VLAN mismatch can cause problems with untagged traffic, it does not prevent all VLAN traffic from passing; the trunk would still carry tagged frames for other VLANs.
B
Distractor review
VLAN 1 has been deleted on one of the switches
VLAN 1 is the default VLAN and cannot be deleted on most Cisco switches.
C
Distractor review
Spanning Tree Protocol is blocking the trunk link
If the link is up and trunking is configured, STP would typically not block a trunk port unless there is a loop. The scenario states the link is up, so STP blocking is unlikely.
D
Best answer
The trunk encapsulation is mismatched
If one switch is configured for ISL encapsulation and the other for 802.1Q, the trunk will not pass traffic because the encapsulation methods are incompatible.
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 trunk encapsulation is mismatched — When two switches are connected and trunking is configured, both ends must use the same encapsulation protocol. Cisco switches support both ISL and 802.1Q. If one side is configured for ISL and the other for 802.1Q, the trunk will not function properly, even though the link may come up. The native VLAN mismatch would cause issues with untagged traffic but not necessarily prevent all VLAN traffic. VLAN 1 cannot be deleted on Cisco switches. Spanning Tree Protocol may block ports, but the link is up and trunking is configured, so STP is not the immediate cause.
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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