CCNA Switching and Network Access Practice Question
In a router-on-a-stick design, what is configured on the physical router interface connected to the switch?
⚠ Common exam trap
Avoid confusing switch VLAN configurations with router subinterface configurations. Remember that routers require subinterfaces for VLAN handling.
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
✓
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.
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
Assigning every VLAN's IP address directly to the physical interface without subinterfaces fails because the router cannot associate incoming frames with specific VLANs. Ethernet frames arriving on a trunk are 802.1Q-tagged, and without logical subinterfaces configured with encapsulation dot1Q, the router treats all traffic as belonging to a single broadcast domain, making inter-VLAN routing impossible.
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
Relying on the switch to perform inter-VLAN routing internally would describe a Layer 3 switch using Switched Virtual Interfaces (SVIs), not a router-on-a-stick. In this design, the router must do the routing, and the switch acts as a Layer 2 trunking device. Without subinterfaces, the router has no VLAN-aware interfaces and therefore cannot route between VLANs, so this option describes an entirely different architecture.
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
In a router-on-a-stick, the physical Ethernet interface is configured as an 802.1Q trunk, and subinterfaces are created for each routed VLAN. Each subinterface is assigned an IP address from that VLAN's subnet and uses encapsulation dot1Q with the matching VLAN ID, allowing the router to receive and forward VLAN-tagged frames. This logical separation enables inter-VLAN routing over a single physical link, which is the core of this design.
- ✗
A serial encapsulation setting for each VLAN
Why it's wrong here
Serial encapsulation settings such as HDLC or PPP are used on WAN serial links, not on the Ethernet trunk used in a router-on-a-stick design. Each routed VLAN requires 802.1Q tagging on a subinterface, not a serial encapsulation. This option confuses the WAN framing protocol with the VLAN tagging method, so it is completely unrelated to the correct configuration.
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
In a router-on-a-stick, the physical Ethernet interface is configured as an 802.1Q trunk, and subinterfaces are created for each routed VLAN. Each subinterface is assigned an IP address from that VLAN's subnet and uses encapsulation dot1Q with the matching VLAN ID, allowing the router to receive and forward VLAN-tagged frames. This logical separation enables inter-VLAN routing over a single physical link, which is the core of this design.
✗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?”
Visual reference
Go deeper
Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
VLAN tagging
VLAN tagging is a method used to identify which VLAN a network frame belongs to as it travels across a trunk link, allowing multiple VLANs to share the same physical connection without mixing their traffic.
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
About these practice questions
Courseiva writes every 200-301 question from scratch — 1,389 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.