This document discusses inter-VLAN routing, including using a router to enable communication between devices on different VLANs, configuring inter-VLAN routing on a router, and troubleshooting common inter-VLAN connectivity issues. It explains that inter-VLAN routing requires a router or layer 3 switch to route traffic between VLANs and that a traditional method uses multiple router interfaces connected to separate VLANs, while router-on-a-stick uses router subinterfaces connected to a layer 2 switch, with each subinterface needing an IP address and associated VLAN number.