This document discusses inter-VLAN routing and different methods for implementing it. It introduces inter-VLAN routing as a process of forwarding traffic between VLANs using a router. There are three main methods discussed: traditional routing using one interface per VLAN, router-on-a-stick using subinterfaces on a single router interface, and switch-based routing using switch virtual interfaces. The document provides detailed explanations and configurations for router-on-a-stick inter-VLAN routing.