Routers select paths for data packets to cross networks and reach their destinations. Routers do this by connecting with different networks and forwarding data from network to network — including LANs, wide area networks (WANs), or autonomous systems, which are the large networks that make up the Internet. In practice, what this means is that routers are necessary for an Internet connection, while switches are only used for interconnecting devices. It’s common for Routers to have built-in Firewalls to provide necessary network security.