1. Recap: VLANs isolate by default
As covered in the VLAN definition guide, devices in the same VLAN talk directly; devices in different VLANs are isolated and need a gateway.
2. Method 1 — Layer-3 switch (SVI)
A Layer-3 switch creates a Switch Virtual Interface (SVI) for each VLAN and acts as that VLAN's gateway. Traffic is routed in hardware, so it is fast and cheap in latency. Best when one switch (or a stack) serves the whole site.
3. Method 2 — Router-on-a-stick
One physical link connects the switch to a router; the link is a trunk, and the router has one sub-interface per VLAN, each with its own IP as that VLAN's gateway. Simpler gear, but the single link is a bottleneck and a failure point.
4. Which to choose
| Layer-3 switch | Router-on-a-stick |
Speed | Hardware, very fast | Depends on router |
Link count | Normal | One trunk (bottleneck) |
Cost | Higher switch | Cheaper router |
Best for | Campus / industrial core | Small branch |
With QoS on the Layer-3 switch you also prioritize the routed traffic.
5. Common pitfalls
6. Summary
Inter-VLAN routing is just "give each VLAN a gateway on a Layer-3 device." Pick a Layer-3 switch for performance, router-on-a-stick for simplicity. Either way, the gateway is what makes isolated VLANs talk.
