ccna certification new horizons

ccna certification new horizons.. Chapter Device Discovery, Maintenance, and Management .Chapter 4 Routing ConceptsThe task at the heart of network interconnection is solving the routing problem; the role of a router is to connect individual networks to each other and to be responsible for the transmission of packets between different networks. At the heart of the router's work is the routing table, which the router uses to determine the best path for forwarding packets. This chapter describes the router components, the router startup process, and the routing decision process.4.1 Router Overview4.1.1 Router Components A router is a special-purpose computer whose primary function is to determine the best path for sending packets and forwarding them to their destination. Like a common PC, a router has components such as a CPU, memory, and ROM. A router does not have components such as a keyboard, mouse, and monitor; however, compared to a computer, a router has more NVRAM, Flash, and a richer type of interface. The various components of a router and their roles are described below.1 CPU: The central processing unit, like a computer, the CPU performs operating system instructions such as system initialization, routing functions, and switching functions.2 Memory: The memory stores the instructions and data that the CPU needs to execute. For example, router configuration files, IP routing tables, ARP tables, etc. are stored in the memory, and the contents of the memory will be lost when the router restarts or loses power.3 Flash: Flash memory, non-volatile memory that can be stored and erased electronically. Flash memory is used to store IOS image files. In most models of Cisco routers, the IOS is stored in flash memory and is copied to RAM for execution only during the boot process. The contents of the flash memory are not lost when the router is rebooted or powered off.4 NVRAM: Non-volatile RAM, used to store the startup-config o Changes to the router configuration are stored in a running-config file in RAM and are executed immediately by the IOS. To save this change information in case the router reboots or loses the file during a power failure, the running-config file must be saved to NVRAM with the storage file name startup-configigo the router reboots or loses power, NVRAM will not lose the contents stored in it.5 ROM: is a type of permanent memory. Cisco devices use ROM to store the bootstrap, basic diagnostic software, and limited function IOS. ROM uses firmware, which is software embedded in the integrated circuit. Firmware contains software that generally does not need to be modified or upgraded, such as boot instructions. The contents of the ROM are not lost when the router is powered down or restarted. Upgrading generally requires replacing the chip.