Using the boot system command

Using the boot system command

5.1.3

This page will explain how boot system commands are used to specify the fallback boot-up sequence for Cisco IOS software.
The three figures show boot system entries. These entries specify that a Cisco IOS software image will load first from flash memory, then from a network server, and finally from ROM:

• Flash memory - A system image can be loaded from flash memory. Information stored in flash memory is not vulnerable to network failures that can occur when system images are loaded from TFTP servers. 
• Network server - If flash memory is corrupted, a system image can be loaded from a TFTP server. 
• ROM - The final bootstrap option is to boot from ROM. However, a system image in ROM is usually a subset of the Cisco IOS that lacks the protocols, features, and configurations of the full Cisco IOS. Also, if the software has been updated, a router may have an older version stored in ROM.  

The command copy running-config startup-config saves the commands in NVRAM. The router will execute the boot system commands as needed in the order in which they were originally entered into configuration mode.
In the Lab Activities, students will use boot system commands to display information about the Cisco IOS image and boot procedure of a router.
The next page will describe the router configuration register.

How a Cisco device locates and loads IOS

 How a Cisco device locates and loads IOS

5.1.2

The default source for Cisco IOS software depends on the hardware platform. Most routers use the boot system commands saved in NVRAM. Cisco IOS software allows several alternatives to be used. Other sources can be specified for the software, or the router can use its own fallback sequence to load the software.
The settings in the configuration register enable the following alternatives:

• Global configuration mode boot system commands can be specified to enter fallback sources for a router to use in sequence. The router will use these commands as needed when it restarts.
• If NVRAM lacks boot system commands that a router can use, the system will use the Cisco IOS software in flash memory by default.
• If flash memory is empty, a router will try to use TFTP to load an IOS image from the network. The router will use the configuration register value to form a filename from which to boot a default system image that is stored on a network server.
• If a TFTP server is unavailable, the router will load the limited version Cisco IOS software image stored in ROM.

The Interactive Media Activity will help students become familiar with the process a Cisco device uses to find and load IOS.
The next page will explain how boot system commands are used.

Router Boot Sequence and Verification

Router Boot Sequence and Verification


5.1.1 Stages of the router power-on boot sequence

This page will describe the router startup sequence.

The goal of the startup routines for Cisco IOS software is to start the router operations. A router must reliably connect any configured networks. To do this, the startup routines must do the following:

• Test the router hardware
• Find and load the Cisco IOS software
• Find and apply configuration statements such as protocol functions and interface addresses

Figure illustrates the sequence and services that are used to initialize a router.

Students can use the Interactive Media Activity to test their familiarity with the router boot sequence.

The next page will describe how a Cisco device finds and loads Cisco IOS.

Chapter 5 : Managing Cisco IOS Software / Overview

Router Boot Sequence and Verification

Overview

This page summarizes the topics discussed in this module.

A Cisco router cannot operate without the Cisco IOS. Each Cisco router has a predetermined boot-up sequence that is used to locate and load the Cisco IOS. This module will describe the stages and importance of this bootup procedure.

Cisco internetworking devices use several different files to operate, such as Cisco IOS images and configuration files. A network administrator must manage these files to ensure that the proper versions are used and that necessary backups are performed. This module also describes the Cisco file system and provides the tools to manage it effectively.

This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams. -

Students who complete this module should be able to perform the following tasks:

• Identify the stages of the router boot sequence
• Determine how a Cisco device locates and loads the Cisco IOS
• Use the boot system command
• Identify the configuration register values
• Briefly describe the files used by the Cisco IOS and their functions
• List the locations of the different file types on a router
• Briefly describe the parts of the IOS name
• Use TFTP and copy-and-paste to save and restore configuration files
• Use TFTP to load an IOS image
• Use XModem to load an IOS image

Use show commands to verify the file system 

Summary

Summary

This page summarizes the topics discussed in this module.

CDP is used to obtain information about directly connected Cisco devices. This includes the router interfaces the devices are connected to, the interfaces used to make the connections, and the model numbers of the devices. CDP is media and protocol independent, and runs on all Cisco equipment over SNAP. It is a Layer 2 protocol that connects lower physical media and upper network layer protocols.

When a Cisco device boots up, CDP starts up automatically and allows the device to detect directly connected Cisco devices that also use CDP. It operates at the data link layer and allows two systems to learn about each other, even if they use different network layer protocols. The show cdp neighbors command is used to display information about the networks that are directly connected to a router.

The cdp run command is used to enable CDP globally on a router. The cdp enable command is used to enable CDP on a particular interface. To disable CDP at the global level, use the no cdp run command in global configuration mode.

The telnet command may be run from the user or privileged EXEC mode. It allows a user to remotely access another device. It is not necessary to enter the command connect or telnet to establish a Telnet connection. To end a Telnet session, use the exit or logout commands. Once the Telnet session is completed, log off the host. The Telnet connection will terminate after ten minutes of inactivity by default or when the exit command is entered at the user or privileged EXEC prompt.

Other connectivity tests include ping and traceroute. The ping command sends a packet to the destination host and then waits for a reply packet from that host. Results from this echo protocol can help determine the path-to-host reliability, delays over the path, and if the host can be reached or is functional. The traceroute command is similar to the ping command, except that instead of testing end-to-end connectivity, traceroute tests each step along the way. This operation can be performed at either the user or privileged EXEC levels.

Troubleshooting IP addressing issues

Troubleshooting IP addressing issues


4.2.6 IP address-related problems are the most common problems that occur on IP networks. This page will describe three commands that are used to perform address-related troubleshooting:

• ping uses the ICMP protocol to verify the hardware connection and the IP address of the network layer. This is a basic test mechanism.
• telnet verifies the application layer software between a source and a destination. This is the most complete test mechanism available.
• traceroute locates failures in a path from a source to a destination. This command uses Time to Live values to generate messages from each router along a path.

The Lab Activity will require students to configure devices in a WAN and then troubleshoot IP address issues.

This page concludes this lesson. The next page will summarize the main points from this module.