Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A network administrator is configuring a router-on-a-stick to route between two VLANs (VLAN 10 and VLAN 20). The router has two subinterfaces: GigabitEthernet0/1.10 with encapsulation dot1Q 10 and IP 10.10.10.1/24, and GigabitEthernet0/1.20 with encapsulation dot1Q 20 and IP 10.10.20.1/24. The switch port connected to the router is configured as an access port in VLAN 10. Hosts in VLAN 10 can ping the router's VLAN 10 interface, but hosts in VLAN 20 cannot ping the router's VLAN 20 interface. 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 router subinterface for VLAN 20 is not enabled.
If the subinterface were not enabled, pings to the VLAN 10 subinterface would also likely fail. The issue is at the switch port, not the router.
B
Best answer
The switch port connecting to the router should be configured as a trunk.
A trunk port carries traffic for multiple VLANs. Since the router uses subinterfaces with 802.1Q encapsulation, the switch must allow tagged frames for both VLANs.
C
Distractor review
The hosts in VLAN 20 do not have a default gateway configured.
The problem is that traffic from VLAN 20 cannot reach the router's subinterface at all; the default gateway is not reachable.
D
Distractor review
The router's VLAN 20 subinterface has an incorrect IP address.
The subinterface is configured correctly; the hosts cannot ping it because the switch port is blocking VLAN 20 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: The switch port connecting to the router should be configured as a trunk. — In a router-on-a-stick configuration, the switch port connecting to the router must be configured as a trunk port to carry traffic for multiple VLANs. An access port only allows frames from one VLAN, so VLAN 20 traffic is dropped by the switch. The router expects tagged frames for VLAN 20, but the switch sends them untagged (or drops them). Configuring the switch port as a trunk will resolve the issue.
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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