ROAS: VLAN Tagging + Trunking in Packet Tracer

Before we begin, a brief note:

While this topology can be simulated on a Layer 3 switch, the Router-on-a-Stick (ROAS) method is an effective teaching exercise that demonstrates VLAN tagging and trunking concepts when a dedicated L3 switch is not available.

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What You’ll Learn

  • How 802.1Q tagging carries multiple VLANs over a single trunk link
  • Subinterfaces on a router (ROAS) and assigning encapsulation + IPs
  • Access ports vs trunk ports in a simple two-VLAN lab
  • Basic inter-VLAN routing flow when you don’t have an L3 switch

Lab Requirements

  • 1x Router supporting subinterfaces
  • 1x Switch configured with one trunk port to the router and access ports to PCs
  • 2+ PCs on different access VLANs

Why ROAS vs L3 Switch SVIs?

  • ROAS is simple and portable, great for Packet Tracer
  • Forces you to understand trunks, tags, and subinterfaces
  • Scales fine for small labs; for bigger networks, SVIs on an L3 switch are cleaner