ccnav7 introduction to networks pdf

ccnav7 introduction to networks pdf.All I0S devices have two components: hardware and software. Almost all I0S-based routers use the same hardware and firmware components to help with the boot process: R0M (read-only memory), RAM (random access memory), flash memory, NVRAM (non-volatile RAM), configuration registers, and physical lines and interfaces. Each of these components can affect how the router boots and how the operating system and configuration files are loaded. The next few subsections describe these components in more depth.15.1.1 Read-Only Memory (ROM)The software in ROM cannot be modified unless the router's ROM chip is replaced. ROM is non-volatile - the contents of ROM do not disappear when the device is turned off. ROM contains the firmware needed to boot the router and typically contains the following three components.. POST (Power-On Self Test): checks the router's hardware components. . Bootloader: boots the router and determines how to find and load 1OS images and configuration files.. ROM Monitor (ROMMON mode): a small operating system that allows you to perform low-level checks and troubleshooting. For example, ROMMONo is required during password recovery To interrupt the normal boot process of the router (without loading the IOS), enter ROMMON mode by pressing Ctrl. In ROMMON mode, the prompt is or rommon>, depending on the router model.Exam Essentials POST performs a hardware self-test; the bootloader boots the router and looks for an IOS image; ROMMON contains a mini-OS for low-level checking and debugging. These components are stored in ROM.15.1.2 Other ComponentsThe router also contains other components to be used during the boot process, which include RAM, flash memory, NVRAM, configuration registers, and physical lines and interfaces. These components are described below.RAM is similar to PC memory. On a router, RAM (in most cases) contains the running IOS image, active configuration files, various tables (routing tables, ARP tables, etc.), and internal buffers for temporary storage of information (interface input and output buffers and log message buffers). The memory is managed by the IOS, and anything in RAM disappears when the router is shut down.Chapter 15 Router Initial Configuration 357