Troubleshooting Methodologies and Tools Chapter Summary

The following section is a summary of the major points you should be aware of in this chapter.

Troubleshooting and the Troubleshooting Flow

1. Troubleshooting can be thought of as the process of identifying or diagnosing a problem
2. There is no single troubleshooting method that can be applied to all situations
3. The high-level three-step troubleshooting flow is comprised of the following phases:

1. The Problem Report
2. Problem Diagnosis
3. Problem Resolution

1. The problem report is what typically initiates the troubleshooting process
2. The problem report is used to define the problem
3. The very first step of the troubleshooting process itself is problem diagnosis
4. The problem diagnosis phase is the most time consuming phase
5. The five steps included in the problem diagnosis phase are:

6. Collecting information about the problem
7. Analyzing or examining the collected information
8. Eliminating possible causes
9. Hypothesizing or theorizing potential causes
10. Verifying the hypothesis or theory

1. The problem resolution phase entails notifying and confirming that the problem is resolved

Communication and Troubleshooting

1. Effective communication is an integral component of the troubleshooting process
2. Effective communication includes the end user, team management, and management
3. Effective communication is essential in all steps of the troubleshooting process

Integrating Maintenance and Troubleshooting

1. A well documented and well maintained network is a lot easier to support and troubleshoot
2. A structured maintenance approach facilitates the troubleshooting and support functions
3. Baselining is a network maintenance function that facilitates troubleshooting
4. Baselining is a process for studying the network and network devices regular intervals
5. Baselining can help you obtain the following information from the network:

1. Information on the health of the hardware and software
2. Predict future problems
3. Determine the current utilization of network resources
4. Identify current network problems
5. Make accurate decisions about network alarm thresholds

1. The baselining process can be used to determine the network break point
2. Baselining tools include Cisco IP SLA operations, SNMP, NetFlow, and CiscoWorks
3. Documentation is integral to the troubleshooting process
4. The network should be well documented and documentation well maintained
5. Tools that facilitate documentation include EEM, Configuration Archive, and KRON
6. Change management also facilitates the troubleshooting process
7. A change management process can help minimize network and service downtime
8. Some examples of changes include the following:

1. Environmental changes
2. Network changes
3. Application changes
4. Hardware changes
5. Documentation changes
6. Software changes

1. Troubleshooting is simplified when changes are implemented in a controlled environment

Troubleshooting Methodologies

1. A structured troubleshooting approach reduces the amount of time spent troubleshooting
2. A structured troubleshooting approach results in greater efficiency
3. Experienced troubleshooters commonly use a shoot from the hip troubleshooting method
4. A shoot from the hip approach leverages the troubleshooters experience and knowledge
5. A shoot from the hip approach will not usually work well for inexperienced troubleshooters
6. Commonly used structured troubleshooting approaches include the following:

1. The Top-Down Troubleshooting Method
2. The Bottom-Up Troubleshooting Method
3. The Follow the Traffic Path Method
4. The Compare Configurations Method
5. The Divide and Conquer Method
6. The Component Swapping Method

1. The top-down approach begins troubleshooting at Layer 7 and works down to Layer 1
2. The bottom-up approach begins troubleshooting at Layer 1 and works up to Layer 7
3. The follow the traffic method requires intimate network and traffic flow knowledge
4. The follow the traffic method is based on the path that traffic takes through the network
5. The compare configurations method compares configurations with working ones
6. The divide and conquer method begins at the middle of the OSI model
7. The divide and conquer method then works up or down depending on the test results
8. The component swapping method physically replaces components

The Cisco IOS Generic Troubleshooting Toolkit

1. Cisco IOS software provides a plethora of tools that can be used to support troubleshooting
2. The Ping and Traceroute utilities are commonly used to verify network connectivity
3. The Ping utility is primarily used to verify connectivity between endpoints
4. The Traceroute utility is primarily used to discover the path taken between endpoints
5. Cisco IOS software supports standard and extended Ping and Traceroute functions
6. Cisco IOS software supports GOLD and IOS Service Diagnostics utilities
7. Cisco GOLD can be used to troubleshoot hardware problems
8. Cisco IOS Service Diagnostics is a programmable diagnostics service
9. Cisco IOS Service Diagnostics can be used for BGP,OSPF, and QoS diagnostics
10. Cisco IOS Service Diagnostics can be used to monitor and detect abnormal utilization
11. Cisco IOS Service Diagnostics leverages EEM and Tcl
12. Cisco commands are filtered using the begin, exclude, include, and section keywords
13. Regular expressions can also be used when performing command filtering
14. Cisco IOS command output can also be redirected to external locations, e.g. Flash and TFTP
15. Cisco IOS command output redirection uses the append, redirect or tee keywords
16. The append keyword appends output to an existing file
17. The redirect keyword redirects the command output to the specified location
18. The tee keyword redirects output and allows you to see it at the same time
19. Analyzing traffic packet captures is one of the most common troubleshooting tasks
20. Cisco IOS software-based routers support RITE for packet captures
21. RITE can be used to send captures to a specified device or store them in memory
22. Cisco Catalyst switches and high-end routers support SPAN for packet captures
23. Cisco provides three variants of SPAN: local SPAN, RSPAN and ERSPAN
24. Local SPAN is configured on a single physical device
25. Remote SPAN can be configured between multiple Layer 2 switches across trunk links
26. ERSPAN can be configured between remote switches separated by IP networks
27. The show processes command can be used for health monitoring and verification
28. The show processes command provides CPU and memory statistics
29. The show environment command is used to verify device environmental variables
30. Cisco provides additional troubleshooting online, e.g. Error Message Decoder