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Routing & Switching · Foundational

Router on a Stick (ROAS)

Inter-VLAN routing using one router interface trunked to a switch with an 802.1Q subinterface per VLAN.

Definition

Each subinterface uses encapsulation dot1Q <vlan> and holds the default gateway for that VLAN. All inter-VLAN traffic shares one physical link, which can become a bottleneck.

Example

interface Gi0/0.20 / encapsulation dot1Q 20 / ip address 10.20.0.1 255.255.255.0

Exam tip

The native VLAN subinterface needs encapsulation dot1Q <vlan> native, or put the IP on the physical interface.

Related terms