Computers and networks

External router configuration sources

In this section, you will learn about the router components that play a key role in the configuration process. Knowing which components are involved in the configuration process gives you a better understanding of how the router stores and uses your configuration commands. Being aware of the steps that take place during router initialization will help

you determine what and where problems may occur when you start up your router.

You can configure a router from many external locations, including the following:

- from the console terminal (a computer connected to the router through a console port) during its installation

-via modem by using the auxiliary port

-from Virtual Terminals 0-4, after it has been installed on the network

-from a TFTP server on the network

Internal router's configuration components

The internal architecture of the Cisco router supports components that play an important role in the startup process. Internal router configuration components are as follows:

RAM/DRAM -- stores routing tables,ARP cache, fast-switching cache,packet buffering (shared RAM), and packet hold queues; RAM also provides temporary and/or running

memory for a router's configuration file while the router is powered; RAM content is lost during a power down or restart

NVRAM -- non-volatile RAM stores the router's backup/startup configuration file; NVRAM content is retained during power down or restart

Flash -- erasable, reprogrammable ROM that holds the operating system image and microcode; Flash memory enables software updates without removing and replacing processor chips; Flash content is retained during power down o restart; Flash memory can store multiple versions of IOS software

ROM -- contains power-on diagnostics, a bootstrap program, and operating system software; software upgrades in ROM require removing and replacing pluggable chips on the CPU interfaces -- network connections on the motherboard or on separate interface modules, through which packets enter and exit a router.

RAM for working storage in the router

RAM is the working storage area for a router. When you turn a router on, the ROM executes a bootstrap program. This program performs some tests, and then loads the Cisco IOS software into memory. The command executive, or EXEC, is one part of the Cisco IOS software. EXEC receives and executes commands you enter for the router.

A router also uses RAM to store an active configuration file and tables of network maps and routing address lists. You can display the configuration file

on a remote or console terminal. A saved version of this file is stored in NVRAM. It is

accessed and loaded into main memory each time a router initializes. The configuration file contains global, process, and interface information that directly affects the operation of a router and its interface ports.

An operating system image cannot be displayed on a terminal screen. An image is

usually executed from the main RAM and loaded from one of several input sources.

The operating software is organized into routines that handle the tasks associated with different protocols, such as data movement, table and buffer management, routing updates, and user command execution.

Router modes

Whether accessed from the console or by a Telnet session through a TTY port, a router can be placed in several modes. Each mode provides different functions:

-user EXEC mode -- This is look-only mode in which the user can view some information about the router, but can change nothing.

-privileged EXEC mode -- This mode supports the debugging and testing commands, detailed examination o the router, manipulation of configuration