200-101 · Question #173
The ROUTE company has a small network. The network consists of one switch and one router. The switch has been configured with two VLANs. The router has been configured as a router-on-a-stick to…
The correct answer is C. two. Router-on-a-stick inter-VLAN routing requires one subinterface per VLAN on the router's physical interface. With two VLANs, exactly two subinterfaces are required.
Question
Options
- Azero
- Bone
- Ctwo
- Dthree
How the community answered
(57 responses)- A2% (1)
- B4% (2)
- C93% (53)
- D2% (1)
Why each option
Router-on-a-stick inter-VLAN routing requires one subinterface per VLAN on the router's physical interface. With two VLANs, exactly two subinterfaces are required.
Zero subinterfaces means only the physical interface is used, which can only belong to one VLAN and cannot bridge traffic between two separate VLANs.
One subinterface can encapsulate traffic for only a single VLAN, leaving the second VLAN without a routed gateway and no path for inter-VLAN communication.
In a router-on-a-stick configuration, each VLAN requires its own dedicated subinterface configured with 802.1Q encapsulation and an IP address acting as the default gateway for that VLAN. With exactly two VLANs on the switch, the router needs exactly two subinterfaces - one per VLAN - to route traffic between them over the single trunk link.
Three subinterfaces exceed the requirement; each VLAN maps to exactly one subinterface, so two VLANs require exactly two, not three.
Concept tested: Router-on-a-stick subinterface count for inter-VLAN routing
Source: https://www.cisco.com/c/en/us/support/docs/lan-switching/inter-vlan-routing/41860-howto-L3-intervlanrouting.html
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