Cisco Systems CCNA 2 manual Router Boot Sequence and Verification

5.1 Router Boot Sequence and Verification

Essential Labs:	5.1.3 and 5.1.5
Optional Labs:	None
Core TIs:	All
Optional TIs:	none

Course-Level Claim: Students can Identify the stages of the router boot-up sequence and show how the configuration-registerand boot system commands modify that sequence.

Certification-Level Claim: Students can describe the components of network devices.

Hands-on skills: none

5.1.1 Stages of the router power-on boot sequence

The purpose of the router boot-up sequence is to verify the operation of hardware and load the correct IOS and configuration file. The router must follow a predefined set of steps while it boots up:

•When the router is first powered-on, it executes the power-on self test (POST). These diagnostics are located in ROM and verify the proper operation of the router hardware.

•If the router passes the POST, the bootstrap loader in ROM executes. The bootstrap basically indicates a starting point in memory that will load other instructions.

•Now the router is ready to load the operating system, which is Cisco IOS. The IOS can be found in flash, TFTP, or ROM. The boot field of the configuration register will indicate the location of the IOS image.

•After the operating system is loaded and operational, the configuration file from NVRAM is loaded and executed. If no configuration file exists in NVRAM, the router will prompt the user to use a question-driven setup menu.

Review the figure in this TI with the students. This is an excellent visual representation of the different aspects of the boot process. Each student should be able to reproduce this figure from memory. Remove the configuration from NVRAM to demonstrate the process used to check for a TFTP server and then enter the setup menu. Demonstrate the use of Ctrl-Cto exit from the setup menu.

5.1.2 How a Cisco device locates and loads the Cisco IOS

The router can load the Cisco IOS from several different locations that can be specified by the operator. The boot system commands can be used to identify a fallback sequence of locations to look for the IOS.

52 - 238 CCNA 2: Routers and Routing Basics v3.1 Instructor Guide – Module 5 Copyright ♥ 2004, Cisco Systems, Inc.