Router-on-a-stick inter-VLAN routing versus a multilayer switch: which statement is true?

Router-on-a-stick inter-VLAN routing versus a multilayer switch: which statement is true?

• A. Router-on-a-stick uses a router subinterface per VLAN, adding routing hops and potential latency; a multilayer switch performs inter-VLAN routing on the switch using SVIs, which is faster but requires capable hardware and careful design
• B. Router-on-a-stick is faster and more scalable than a multilayer switch
• C. A multilayer switch cannot route between VLANs
• D. Both approaches require external routers for inter-VLAN routing

Answer: (A)

Inter-VLAN routing can be implemented either with a router-on-a-stick or with a multilayer switch, and the key difference is where the routing happens and how it affects performance and design. In router-on-a-stick, a router is connected to a trunk, and you create a separate subinterface for each VLAN. Each subinterface has an IP address in its VLAN, and inter-VLAN traffic must travel from the source VLAN to the router, be routed, and then return to the destination VLAN. That means extra hops and more traffic on the link to the router, which can add latency and become a bottleneck as the network grows or traffic increases. With a multilayer switch, routing between VLANs happens inside the switch itself using SVIs (Switched Virtual Interfaces) for each VLAN. The switch can perform the routing in hardware, so inter-VLAN traffic stays within the switch fabric and avoids the external router hop, resulting in lower latency and higher throughput on many platforms. However, this approach requires L3-capable hardware and careful design to ensure the switch has enough performance and features (routing protocols, ACLs, QoS, etc.) to meet the network’s needs. The other statements are less accurate: router-on-a-stick is not inherently faster or more scalable than an MLS; a multilayer switch can route between VLANs, so it does not necessarily require an external router for inter-VLAN routing.

Inter-VLAN routing can be implemented either with a router-on-a-stick or with a multilayer switch, and the key difference is where the routing happens and how it affects performance and design. In router-on-a-stick, a router is connected to a trunk, and you create a separate subinterface for each VLAN. Each subinterface has an IP address in its VLAN, and inter-VLAN traffic must travel from the source VLAN to the router, be routed, and then return to the destination VLAN. That means extra hops and more traffic on the link to the router, which can add latency and become a bottleneck as the network grows or traffic increases.

With a multilayer switch, routing between VLANs happens inside the switch itself using SVIs (Switched Virtual Interfaces) for each VLAN. The switch can perform the routing in hardware, so inter-VLAN traffic stays within the switch fabric and avoids the external router hop, resulting in lower latency and higher throughput on many platforms. However, this approach requires L3-capable hardware and careful design to ensure the switch has enough performance and features (routing protocols, ACLs, QoS, etc.) to meet the network’s needs.

The other statements are less accurate: router-on-a-stick is not inherently faster or more scalable than an MLS; a multilayer switch can route between VLANs, so it does not necessarily require an external router for inter-VLAN routing.