These routers generally only provide the most basic routing functions when they leave the factory. Users can select the corresponding module according to the type of network to be connected. Different modules can provide different connection and management functions. For example, most modular routers can allow users to select the type of network interface, some modular routers can provide functional modules such as VPN, and some modular routers also provide firewall functions and so on. Most routers are modular routers.