Troubleshooting Methodologies

CCNA Course

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Table of Contents

Describe common network troubleshooting methodologies.

Step	Description
Step 1. Identify the Problem	This is the first step in the troubleshooting process. Although tools can be used in this step, a conversation with the user is often very helpful.
Step 2. Establish a Theory of Probable Causes	After the problem is identified, try to establish a theory of probable causes. This step often yields more than a few probable causes to the problem.
Step 3. Test the Theory to Determine Cause	Based on the probable causes, test your theories to determine which one is the cause of the problem. A technician may apply a quick fix to test and see if it solves the problem. If a quick fix does not correct the problem, you might need to research the problem further to establish the exact cause.
Step 4. Establish a Plan of Action and Implement the Solution	After you have determined the exact cause of the problem, establish a plan of action to resolve the problem and implement the solution.
Step 5. Verify Solution and Implement Preventive Measures	After you have corrected the problem, verify full functionality. If applicable, implement preventive measures.
Step 6. Document Findings, Actions, and Outcomes	In the final step of the troubleshooting process, document your findings, actions, and outcomes. This is very important for future reference.

In some situations, it may not be possible to resolve the problem immediately. A problem should be escalated when it requires a manager decision, some specific expertise, or network access level unavailable to the troubleshooting technician.
A company policy should clearly state when and how a technician should escalate a problem.

The IOS debug command allows the administrator to display OS process, protocol, mechanism and event messages in real-time for analysis.
All debug commands are entered in privileged EXEC mode.
The Cisco IOS allows for narrowing the output of debug to include only the relevant feature or subfeature.
Use debug commands only to troubleshoot specific problems.
- To list a brief description of all the debugging command options, use the debug ? command in privileged EXEC mode at the command line.
- To turn off a specific debugging feature, add the no keyword in front of the debug command
- Alternatively, you can enter the undebug form of the command in privileged EXEC mode.
- To turn off all active debug commands at once, use the undebug all command.
Be cautious using some debug commands, as they may generate a substantial amount of output and use a large portion of system resources.
The router could get so busy displaying debug messages that it would not have enough processing power to perform its network functions, or even listen to commands to turn off debugging.

debug and certain other IOS message output is not automatically displayed on remote connections. This is because log messages are prevented from being displayed on vty lines.

To display log messages on a terminal (virtual console), use the terminal monitor privileged EXEC command.
To stop logging messages on a terminal, use the terminal no monitor privileged EXEC command.

Topic Title	Topic Objective
Devices in a Small Network	Identify the devices used in a small network.
Small Network Applications and Protocols	Identify the protocols and applications used in a small network.
Scale to Larger Networks	Explain how a small network serves as the basis of larger networks.
Verify Connectivity	Use the output of the ping and tracert commands to verify connectivity and establish relative network performance.
Host and IOS Commands	Use host and IOS commands to acquire information about the devices in a network.
Troubleshooting Methodologies	Describe common network troubleshooting methodologies.
Troubleshooting Scenarios	Troubleshoot issues with devices in the network.

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