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11.3 Router Components
Router Components Section 11: Exploring the Functions of Routing Cisco offers a number of different routers, which come in many shapes and sizes. The various models offer a variety of features that are suitable for an array of different environments. However, the core function of a router is to route packets, and for that reason, all routers have a number of common components. These components include: CPU: The CPU, or processor, is the chip that is installed on the motherboard that carries out the instructions of a computer program. For example, it processes all the information that is gathered from other routers or sent to other routers. Motherboard: The motherboard is the central circuit board, which holds critical electronic components of the system. The motherboard provides connections to other peripherals and interfaces. Memory: There are four primary types of memory: RAM: RAM is memory on the motherboard that stores data during CPU processing. It is a volatile type of memory in that its information is lost when power is switched off. RAM provides temporary memory for the running configuration of the router while the router is powered on. NVRAM: NVRAM retains content when the router is powered down. NVRAM stores the startup configuration file for most router platforms. It also contains the software configuration register, which is used to determine which image to use when booting the router. ROM: ROM is readonly memory on the motherboard. The content of ROM is not lost when power is switched off. Data that is stored in ROM cannot be modified, or it can be modified only slowly or with difficulty. ROM sometimes contains ROM monitor, which provides a user interface when the router cannot find a valid image, and bootloader software, which helps the router boot when it cannot find a valid Cisco IOS image in flash memory. Flash: Flash memory is nonvolatile storage that can be electrically erased and reprogrammed. Flash memory stores the Cisco IOS Software image. On some platforms, it can also store configuration files or boot images. Ports: Ports are used to connect routers to other devices in the network. Routers can have these types of ports: Management ports: Management ports are for the connection of a terminal that is used for management. Routers have a console port that can be used to attach to a terminal that is used for management, configuration, and control. Highend routers may also have a dedicated Ethernet port that can be used only for management. An IP address can be assigned to the Ethernet port, and the router can be accessed from a management subnet. The AUX interface on a router is used for remote management of the router. Typically, a modem is connected to the AUX interface for dialin access. From a security standpoint, enabling the option to connect remotely to a network device carries with it the responsibility of vigilant device management. Network ports: The router has a number of network ports, including various LAN or WAN media ports, which may be copper or fiber cable. IP addresses are assigned to network ports. As an example, the following figure shows the ports on a Cisco ASR 1001 Router: Up Next: Routing Table