Router-on-a-stick is the classic technique for routing between VLANs using a router with only one physical interface to a switch. The interface becomes a trunk; the router has a virtual subinterface for each VLAN, each with its own IP address and its own VLAN ID via 802.1Q encapsulation. The result: the router can route between VLANs even though it has only one cable to the switch. This lab configures it on the base topology with R1 + SW1.
What you will learn
- The router-on-a-stick architecture: trunk to the switch, subinterfaces with dot1Q encapsulation
- How to configure a subinterface and assign it to a VLAN
- How to configure a switchport as a trunk that carries multiple VLANs to a router
- The output of
show vlanson a router (the router-side VLAN table) - The historic vs modern use case (when this is the right design vs when SVI on L3 switch wins)
What this lab does NOT cover
- SVI on L3 switch (the modern alternative) - that is na-13
- Multiple physical interfaces to the same switch (typical of pre-trunk designs)
- Inter-VLAN routing on a multi-area OSPF design
Topology
Download the PingLabz CCNA Base Topology .yaml
The PingLabz CCNA Base Topology - three iol-xe routers + one alpine host + one ioll2-xe managed switch + one unmanaged switch. The reusable foundation.
