220-1101 Networking Practice Question
A network technician is configuring a small office network with one router and one managed switch. The switch has two VLANs: VLAN 10 for Sales and VLAN 20 for Engineering. Both VLANs need internet access. The technician configures the router's single physical interface (G0/0) with subinterfaces G0/0.10 for VLAN 10 (192.168.10.1/24) and G0/0.20 for VLAN 20 (192.168.20.1/24). The switch port connected to the router is configured as an access port in VLAN 10. Which of the following is the MOST likely result of this configuration?
⚠ Common exam trap
A common mix-up: candidates assume configuring subinterfaces on the router automatically enables all VLANs, but they overlook that the switch port must be a trunk to carry multiple VLANs; an access port restricts traffic to a single VLAN.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Only devices in VLAN 10 can access the internet.
The switch port connected to the router is configured as an access port in VLAN 10. This means it only carries traffic for VLAN 10, stripping any VLAN tags. The router's subinterface G0/0.20 for VLAN 20 never receives or sends traffic because the access port does not allow VLAN 20 frames. Therefore, only devices in VLAN 10 can reach the router's default gateway (192.168.10.1) and access the internet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Only devices in VLAN 10 can access the internet.
Why this is correct
Because the switch port connecting to the router is configured as an access port in VLAN 10, the switch forwards only VLAN 10 frames out that port, and it sends them untagged. The router receives these as ordinary IP traffic on its LAN interface and can route them to the internet. VLAN 20 frames are never carried over an access port assigned to VLAN 10, so devices in VLAN 20 have no Layer 2 path to the router and therefore no internet access.
- ✗
Both VLAN 10 and VLAN 20 can access the internet.
Why it's wrong here
This would only be possible if the switch port were configured as a trunk allowing both VLANs, or if inter-VLAN routing were configured on the switch. The current configuration prevents VLAN 20 traffic from reaching the router.
- ✗
Only devices in VLAN 20 can access the internet.
Why it's wrong here
An access port in VLAN 10 removes VLAN tags and forwards only the single configured VLAN's frames, so VLAN 20 traffic never reaches the router through that port. Without a trunk link to the router or inter-VLAN routing on the switch, VLAN 20 hosts have no routed path to the default gateway or ISP. Consequently, VLAN 20 is isolated from the internet, while VLAN 10 remains fully connected because its frames are the only ones the access port transmits.
- ✗
Neither VLAN can access the internet.
Why it's wrong here
The statement that neither VLAN can access the internet is incorrect because VLAN 10 traffic does reach the router: the access port forwards VLAN 10 frames untagged to the router's LAN interface, allowing those hosts to route out to the ISP. The setup does not block all traffic; it blocks only VLAN 20 traffic, since the access port is not configured for that VLAN and no other routed path exists for it. Therefore, VLAN 10 has internet connectivity while VLAN 20 does not, making a blanket 'neither' claim technically false.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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