Lab: Layer 3 Switching Pt.2 – Inter VLAN Routing with Router on a Stick


With the Layer 3 Switch set up in Pt.1  it is time to look at some basic concepts of Layer 3 Switching. The Router on a Stick concept is technically not Layer 3 Switching since the Packet Forwarding (Routing) requires a Router.

The basic concept of Router on a stick is implemented by creating subinterfaces on a single physical Router port. After the Switchport has been set to trunk mode (802.1q for you non-Cisco networkers), the subinterfaces can be assigned a VLAN by setting the trunk encapsulation to dot1q and a VLAN ID.






This concept should work with any switch that supports VLANs. Another advantage of this concept is the fact that only one Router port is required in order to forward Layer 3 packets between the VLANs. The downsides however are a single point of failure and possible congestion (depending on the amount of VLANs and bandwidth utilization).

Coming up next: Inter-VLAN Routing with Switched Virtual Interfaces (SVI) and Routed Ports which require Layer 3 switches.