The correct answer is subinterfaces with 802.1Q encapsulation configured on the physical router interface. In a router-on-a-stick design, a single physical Ethernet link carries traffic for multiple VLANs, so the router must logically separate these VLANs by creating subinterfaces. Each subinterface is assigned an IP address for its respective VLAN and uses 802.1Q encapsulation to tag frames, allowing the router to identify which VLAN a packet belongs to as it routes between them. On the CCNA 200-301 v2 exam, this concept tests your understanding of inter-VLAN routing fundamentals and the distinction between Layer 2 switching and Layer 3 routing. A common trap is thinking you assign IP addresses directly to the physical interface or that the switch performs the routing—neither is correct. Remember the memory tip: “One wire, many VLANs—subinterfaces with dot1q tags.”
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
In a router-on-a-stick design, what is configured on the physical router interface connected to the switch?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Subinterfaces with 802.1Q encapsulation for each routed VLAN
Router-on-a-stick uses one physical router interface with multiple logical subinterfaces. Each subinterface is associated with a VLAN using 802.1Q encapsulation and gets an IP address for that VLAN. Option A is wrong because IP addresses are configured on subinterfaces, not directly on the physical interface for all VLANs. Option B is wrong because inter-VLAN routing requires a router; the switch alone does not perform inter-VLAN routing in this design. Option D is wrong because serial encapsulation is used for WAN connections, not for VLAN tagging on Ethernet interfaces.
Key principle: Router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
One IP address for every VLAN on the physical interface itself only
Why it's wrong here
Putting every VLAN address directly on the parent interface does not provide the required VLAN separation.
When this WOULD be correct
If the question were about a scenario where a single VLAN is being routed directly on the physical interface without the need for subinterfaces, then this option would be correct. For example, a question might specify a simple network setup with only one VLAN requiring a single IP address.
✗
No subinterfaces; the switch handles all inter-VLAN routing internally
Why it's wrong here
That describes multilayer switching, not router-on-a-stick.
When this WOULD be correct
If the question were about a Layer 3 switch that performs inter-VLAN routing internally without needing a router, then this option would be correct. In that context, the switch would manage all VLAN traffic without requiring subinterfaces on the router.
✓
Subinterfaces with 802.1Q encapsulation for each routed VLAN
Why this is correct
Correct. Subinterfaces with dot1q encapsulation are the key configuration element.
Related concept
Router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs.
✗
A serial encapsulation setting for each VLAN
Why it's wrong here
Serial encapsulation is unrelated to VLAN trunking on Ethernet.
When this WOULD be correct
If the exam question asked about a scenario involving a legacy network design where each VLAN is routed over a serial link, then specifying a serial encapsulation setting for each VLAN would be correct. This could occur in a question focused on older technologies or specific routing protocols that utilize serial connections.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Subinterfaces with 802.1Q encapsulation for each routed VLANCorrect answer▾
Why this is correct
Correct. Subinterfaces with dot1q encapsulation are the key configuration element.
✗One IP address for every VLAN on the physical interface itself onlyWrong answer — click to see why▾
Why this is wrong here
Assigning multiple IP addresses directly to the physical interface does not provide VLAN separation; the router cannot distinguish which VLAN a frame belongs to without subinterfaces and 802.1Q encapsulation.
★ When this WOULD be the correct answer
If the question were about a scenario where a single VLAN is being routed directly on the physical interface without the need for subinterfaces, then this option would be correct. For example, a question might specify a simple network setup with only one VLAN requiring a single IP address.
Why candidates choose this
Students may think that configuring multiple IP addresses on a single interface is sufficient for inter-VLAN routing, confusing it with secondary IP addressing on a router interface.
✗No subinterfaces; the switch handles all inter-VLAN routing internallyWrong answer — click to see why▾
Why this is wrong here
In router-on-a-stick, the router performs inter-VLAN routing, not the switch. The switch only forwards frames to the router over a trunk link; internal switching would require a multilayer switch.
★ When this WOULD be the correct answer
If the question were about a Layer 3 switch that performs inter-VLAN routing internally without needing a router, then this option would be correct. In that context, the switch would manage all VLAN traffic without requiring subinterfaces on the router.
Why candidates choose this
This option describes a multilayer switch configuration, which is a common alternative to router-on-a-stick, leading students to confuse the two designs.
✗A serial encapsulation setting for each VLANWrong answer — click to see why▾
Why this is wrong here
Serial encapsulation (e.g., HDLC, PPP) is used on WAN serial links, not on Ethernet interfaces for VLAN trunking. Router-on-a-stick uses Ethernet interfaces with 802.1Q encapsulation.
★ When this WOULD be the correct answer
If the exam question asked about a scenario involving a legacy network design where each VLAN is routed over a serial link, then specifying a serial encapsulation setting for each VLAN would be correct. This could occur in a question focused on older technologies or specific routing protocols that utilize serial connections.
Why candidates choose this
The term 'encapsulation' is used in both contexts (serial and VLAN), causing confusion. Students may mistakenly think serial encapsulation settings apply to VLAN trunking.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Avoid confusing switch VLAN configurations with router subinterface configurations. Remember that routers require subinterfaces for VLAN handling.
Detailed technical explanation
How to think about this question
Router-on-a-stick is a network design where a single physical router interface is used to route traffic between multiple VLANs on a switch. This is achieved by creating multiple logical subinterfaces on the router's physical interface, each representing a different VLAN. Each subinterface is configured with an IP address and uses 802.1Q encapsulation to tag traffic with the appropriate VLAN ID, enabling the router to distinguish and route traffic between VLANs correctly.
The key configuration rule in router-on-a-stick is that the physical interface itself does not have an IP address assigned directly. Instead, each subinterface is assigned an IP address corresponding to its VLAN. The router uses 802.1Q encapsulation on each subinterface to identify VLAN tags on incoming frames. This encapsulation allows the router to process traffic for multiple VLANs over a single physical link, which is typically connected to a trunk port on the switch.
A common exam trap is to incorrectly assign one IP address directly on the physical interface for all VLANs, which breaks VLAN separation and routing functionality. Another confusion is to assume that the switch handles inter-VLAN routing internally without subinterfaces, which describes multilayer switching, not router-on-a-stick. Practically, router-on-a-stick is useful in smaller networks or lab environments where a single router interface must handle multiple VLANs, but it can become a bottleneck in larger networks due to bandwidth limitations on the single physical link.
KKey Concepts to Remember
Router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs.
Each subinterface on the router is configured with an IP address specific to its VLAN to enable inter-VLAN routing.
802.1Q encapsulation is applied on each subinterface to tag traffic with the VLAN ID for proper VLAN identification.
The physical router interface itself does not have an IP address assigned when using router-on-a-stick.
Switch ports connected to the router interface must be configured as trunk ports to carry multiple VLANs.
Router-on-a-stick design is distinct from multilayer switching, which performs inter-VLAN routing within the switch.
Assigning one IP address directly on the physical interface for all VLANs breaks VLAN separation and routing.
Router-on-a-stick can create a bandwidth bottleneck since all VLAN traffic shares a single physical interface.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs., then practise related 200-301 questions on the same topic to reinforce the concept.
Switching and Network Access — This question tests Switching and Network Access — Router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs..
What is the correct answer to this question?
The correct answer is: Subinterfaces with 802.1Q encapsulation for each routed VLAN — Router-on-a-stick uses one physical router interface with multiple logical subinterfaces. Each subinterface is associated with a VLAN using 802.1Q encapsulation and gets an IP address for that VLAN. Option A is wrong because IP addresses are configured on subinterfaces, not directly on the physical interface for all VLANs. Option B is wrong because inter-VLAN routing requires a router; the switch alone does not perform inter-VLAN routing in this design. Option D is wrong because serial encapsulation is used for WAN connections, not for VLAN tagging on Ethernet interfaces.
What should I do if I get this 200-301 question wrong?
Review router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Router-on-a-stick uses a single physical router interface divided into multiple logical subinterfaces to route between VLANs.
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