Chapter 12: Troubleshooting Networking Problems Network+ Guide to Networks Third Edition

Network +2 Objectives: Describe the elements of an effective troubleshooting methodology Follow a systematic troubleshooting process to solve networking problems Use a variety of software and hardware tools to diagnose problems Discuss practical issues related to troubleshooting

Network +3 Troubleshooting Methodology Identify the Symptoms Identify the Scope of the Problem Establish What Has Changed Determine the Most Probable Cause Verify user competency Re-create the problem Verify physical connectivity Verify logical connectivity

Network +4 Troubleshooting Methodology (continued) Recognize the potential effects of a solution Implement a solution Test the solution Document the solution

Network +5 Troubleshooting Methodology (continued)

Network +6 Troubleshooting Methodology (continued) Identify the Symptoms Access to the network affected Network performance affected Data or programs affected Only certain network services affected

Network +7 Troubleshooting Methodology (continued) Identify the Symptoms (continued) If programs are affected, does the problem include one local application, one networked application, or multiple networked applications What specific error messages do users report One user or are multiple users affected Do symptoms manifest themselves consistently

Network +8 Troubleshooting Methodology (continued) Identify the Scope of the Problem How many users or network segments are affected? One user or workstation? A workgroup? A department? One location within an organization? An entire organization?

Network +9 Troubleshooting Methodology (continued) Identify the Scope of the Problem (continued) When did the problem begin? Has the network, server, or workstation ever worked properly? Did the symptoms appear in the last hour or day? Have the symptoms appeared intermittently for a long time? Do the symptoms appear only at certain times?

Network +10 Troubleshooting Methodology (continued)

Network +11 Troubleshooting Methodology (continued)

Network +12 Troubleshooting Methodology (continued) Establish What Has Changed Did the operating system or configuration on a server, workstation, or connectivity device change? Were new components added to a server, workstation, or connectivity device? Were old components removed from a server, workstation, or connectivity device? Were new users or segments added to the network?

Network +13 Troubleshooting Methodology (continued) Establish What Has Changed (continued) Was a server, workstation, or connectivity device moved from its previous location to a new location? Was a server, workstation, or connectivity device replaced? Was new software installed on a server, workstation, or connectivity device? Was old software removed from a server, workstation, or connectivity device?

Network +14 Troubleshooting Methodology (continued) Select the Most Probable Cause Verify User Competency Re-create the Problem Can you make the symptoms recur every time? If symptoms recur, are they consistent? Can you make the symptoms recur some of the time? Do the symptoms happen only under certain circumstances?

Network +15 Troubleshooting Methodology (continued) Select the Most Probable Cause Re-create the Problem (continued) In the case of software malfunctions, are the symptoms consistent no matter how many and which programs or files the user has open? Do the symptoms ever happen when you try to repeat them?

Network +16 Troubleshooting Methodology (continued) Select the Most Probable Cause Verify Physical Connectivity Symptoms of Physical Layer Problems Lengths exceed standards Noise affecting a signal Improper connections Damaged cables Faulty NICs

Network +17 Troubleshooting Methodology (continued) Select the Most Probable Cause Verify Physical Connectivity Diagnosing Physical Layer Problems Device turned on NIC properly inserted Device’s network cable properly connected Patch cables properly connect

Network +18 Troubleshooting Methodology (continued) Select the Most Probable Cause Verify Physical Connectivity Diagnosing Physical Layer Problems (continued) Hub, router, or switch properly connected to the backbone Cables in good condition Connectors in good condition and properly seated Network lengths conform to specifications? Devices configured properly

Network +19 Troubleshooting Methodology (continued) Select the Most Probable Cause Verify Physical Connectivity Swapping Equipment If you suspect a problem lies with a network component

Network +20 Troubleshooting Methodology (continued)

Network +21 Troubleshooting Methodology (continued) Select the Most Probable Cause Verify Logical Connectivity Do error messages reference damaged or missing files or device drivers? Do error messages reference malfunctioning or insufficient resources (such as memory)? Has an operating system, configuration, or application been recently changed, introduced, or deleted? Does the problem occur with only one application or a few, similar applications?

Network +22 Troubleshooting Methodology (continued) Select the Most Probable Cause Verify Logical Connectivity Does the problem happen consistently? Does the problem affect a single user or one group of users?

Network +23 Troubleshooting Methodology (continued) Recognize the Potential Effects of a Solution Scope Tradeoffs Security Scalability Cost Using Vendor Information

Network +24 Troubleshooting Methodology (continued) Implement a Solution Implement a safe and reliable solution: 1. Collect documentation about a problem’s symptoms 2. Backup existing software and keep the old parts handy 3. Perform the change and record your actions 4. Test your solution

Network +25 Troubleshooting Methodology (continued) Implement a Solution Implement a safe and reliable solution: 5. Before leaving the area clean it up 6. Record the details you have collected about the symptoms, the problem, and the solution 7. If solution involved a significant change or problem, revisit the solution a day or two later to verify that the problem has been solved

Network +26 Troubleshooting Methodology (continued) Test the Solution Document Problems and Solutions Staff Involved in Troubleshooting Recording Problems and Resolutions

Network +27 Troubleshooting Methodology (continued) A typical problem record form should include The name, department, and phone number of the problem originator Information regarding whether the problem is software- or hardware-related If the problem is software-related, the package to which it pertains; if the problem is hardware- related, the device or component to which it pertains

Network +28 Troubleshooting Methodology (continued) A typical problem record form should include (continued) Symptoms of the problem, including when it was first noticed The name and telephone number of the network support contact The amount of time spent troubleshooting the problem The resolution of the problem

Network +29 Troubleshooting Methodology (continued) Notifying Others of Changes A change management system Adding or upgrading software Adding or upgrading hardware or other devices Adding new hardware Changing the properties of a network device

Network +30 Troubleshooting Methodology (continued) A change management system (continued) Increasing or decreasing rights Physically moving networked devices Moving user accounts and their files/directories Making changes in processes Making changes in vendor policies or relationships

Network +31 Troubleshooting Methodology (continued) Preventing Future Problems Review the troubleshooting questions and examples Predict network problems by network maintenance, documentation, security, or upgrades

Network +32 Troubleshooting Tools Crossover Cable Use to directly interconnect two nodes Tone Generator and Tone Locator Tone generator is a small electronic device that issues a signal on a wire pair Tone locator is a device that emits a tone when it detects electrical activity on a wire pair

Network +33 Troubleshooting Tools (continued)

Network +34 Troubleshooting Tools (continued) Multimeter Can measure many characteristics of an electric circuit, including its resistance and voltage

Network +35 Troubleshooting Tools (continued)

Network +36 Troubleshooting Tools (continued) Use a multimeter to: Verify that a cable is properly conducting electricity Check for the presence of noise on a wire Verify that the amount of resistance on coaxial cable Test for short or open circuits in the wire

Network +37 Troubleshooting Tools (continued) Cable Continuity Testers In troubleshooting a Physical layer problem, you may find the cause of a problem by simply testing whether your cable is carrying a signal to its destination

Network +38 Troubleshooting Tools (continued)

Network +39 Troubleshooting Tools (continued) Cable Performance Testers Measure the distance to a connectivity device, termination point, or cable fault Measure attenuation along a cable Measure near-end crosstalk between wires Measure termination resistance and impedance

Network +40 Troubleshooting Tools (continued) Cable Performance Testers (continued) Issue pass/fail ratings for CAT 3, CAT 5, CAT 5e, CAT 6, or CAT 7 standards Store and print cable testing results or directly save data to a computer database Graphically depict a cable’s attenuation and crosstalk characteristics over the length of the cable

Network +41 Troubleshooting Tools (continued)

Network +42 Troubleshooting Tools (continued) Network Monitors Continuously monitor network traffic on a segment Capture network data transmitted on a segment Capture frames sent to or from a specific node Reproduce network conditions Generate statistics about network activity

Network +43 Troubleshooting Tools (continued) Network Monitors (continued) Discover all network nodes on a segment Establish a baseline that reflects network traffic Store traffic data and generate reports Trigger alarms when traffic conditions meet preconfigured conditions

Network +44 Troubleshooting Tools (continued) Abnormal data patterns and packets Local collisions Late collisions Runts Giants

Network +45 Troubleshooting Tools (continued) Abnormal data patterns and packets (continued) Jabber Negative frame sequence checks Ghosts Protocol Analyzers Can capture traffic Can also analyze frames To Layer 7 of the OSI Model

Network +46 Troubleshooting Tools (continued)

Network +47 Troubleshooting Tools (continued) Wireless Network Testers Learn about a wireless environment by viewing the wireless network connection properties on your workstation

Network +48 Troubleshooting Tools (continued)

Network +49 Troubleshooting Tools (continued) Wireless network testing tools Identify transmitting APs, stations and channels Measure signal strength and range Indicate the effects of attenuation, signal loss, and noise Interpret signal strength information

Network +50 Troubleshooting Tools (continued) Wireless network testing tools (continued) Ensure proper association and reassociation Capture and interpret traffic Measure throughput and assess data Analyze the characteristics of each channel

Network +51 Troubleshooting Tools (continued)

Network +52 Chapter Summary Before you can resolve a network problem, you need to determine its cause Act like a doctor diagnosing a patient Identify the scope of the problem At each point, stop to consider Ensure that the user is performing all functions correctly

Network +53 Chapter Summary (continued) Attempt to reproduce the problem’s symptoms Check for sound connections Exchange component for a functional one Determine properly configured software Consult vendor information

Network +54 Chapter Summary (continued) Test your solution Operate a help desk Use a software program for documenting Record details about a problem Follow up

Network +55 Chapter Summary (continued) Change management system Tone generator and tone locator Multimeter Cable continuity testers Cable performance tester

Network +56 Chapter Summary (continued) Network monitor Protocol analyzers Wireless network testing tools