Inter-VLAN routing, also known as “router on a stick,” involves multiple VLANs connected with switches via trunks, using a single router to allow a degree of communication between the VLANs and access to the Internet. Since the separation of networks is virtual, the router isn’t placed between them; rather, it’s typically off to the side in the network topology, leading to the eponymous “stick” formation.
While inter-VLAN routing is relatively simple to set up compared to other network topologies to support similar needs, it does have a few disadvantages, because the router constitutes a single point of failure and may become a bottleneck. In addition, the switch connecting to the router may introduce additional latency.
Nevertheless, for relatively small networks, inter-VLAN routing can make sense as a cost-effective way to support multiple VLANs. It uses switches that don’t need layer-3 capability, plus a single router. So in a small network, when you need routing with some degree of separation between subdivisions that may not necessarily correspond to where the nodes are physically located, VLANs with inter-VLAN routing can be a sensible option.