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. 

Alternative connectivity tests

Alternative connectivity tests
4.2.5 This page will introduce some tools that are used to verify basic network connectivity.

Many network protocols support an echo protocol. Echo protocols are used to test if protocol packets are routed. 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 evaluate the path-to-host reliability, delays over the path, and whether the host can be reached or is functional. This is a basic test mechanism. This operation can be performed at either the user or privileged EXEC modes.

In Figure , the ping target 172.16.1.5 responded to all five datagrams that were sent. Each exclamation point (!) indicates a successful echo. Each period (.) on the display indicates that the application on the router timed out while it waited for a packet echo from a target. The ping user EXEC command can be used to diagnose basic network connectivity. The ping command uses Internet Control Message Protocol (ICMP).

The traceroute command, which is often referred to as the trace command in reference materials, can be used to find where data is sent in a network. The traceroute command is similar to the ping command. The main difference is that ping tests end-to-end connectivity and traceroute tests each step along the way. This operation can be performed at either the user or privileged EXEC levels.

In Figure , the path from York to Rome is traced. Along the way the path must go through London and Paris. If one of these routers is unreachable, three asterisks (*) will be returned instead of the name of the router. The traceroute command will attempt to reach the next step until the Ctrl-Shift-6 escape sequence is used.

A basic verification test also focuses on the network layer. Use the show ip route command to see if a routing table entry exists for the target network. This command will be discussed in more detail in a later module of this course.

The procedure to use the ping command is as follows:

• Enter the ping [IP address or name of destination ] command.
• Press the Enter key.

The procedure to use the traceroute command is as follows:

• Enter the traceroute [IP address or name of destination ] command.
• Press the Enter key.

The Lab Activities on this page will allow students to practice three network connectivity tests.

The next page will introduce some tools that are used to troubleshoot IP address-related problems.

Advanced Telnet operation

Advanced Telnet operation
4.2.4 This page will describe some features that can be used when several Telnet sessions are open at the same time. A user may switch back and forth between these sessions. The number of open sessions that are allowed at one time is defined by the session limit command.

Use the commands shown in Figure to escape from one session and resume a previously opened session.

A new connection can be made from the EXEC prompt.

Multiple Telnet sessions can be used and suspended with the Ctrl-Shift-6, then x sequence. The session can be resumed with the Enter key. When the Enter key is used, the Cisco IOS will resume the connection to the most recently suspended Telnet connection. If the resume command is used it requires a connection ID. Use the show sessions command to view the connection ID, as shown in Figure .

The Lab Activity on this page will show students how to use Telnet to remotely access routers.

The next page will describe some tests that can be used to verify connectivity.