CCNP TSHOOT Learning Guide/Chapter 2

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Trobleshooting Processes for Complex Enterprise Networks

Introduction to Troubleshooting Processes

Troubleshooting Methods

Defining Troubleshooting

  • Step 1: Problem Report
  • Step 2: Problem Diagnosis
  • Step 3: Problem resolution

Diagnosing a Problem

Diagnosing a Problem
Step Description
Collect Information A problem report often lacks sufficient information. Collect additional information from. fx. Network Management tolls or interviewing the user.
Examine Collected Information Examine collected information. Fx. comparing to baseline information.
Eliminate Potential causes Based on knowledge of network and collected information - start to eliminate causes.
Hypothesize Underlying Cause After eliminating causes hypothesize the most likely cause of the problem.
Verify Hypothesis Test if the hypothesize resolve the problem

The Value of a Structured Troubleshooting Approach

Structured Troubleshooting Approach
Shoot from the hip Troubleshooting Approach

Popular Troubleshooting Methods

Top-down, Bottom-up or Divide and conquer approaches
Follow the Path of Traffic
Component Swapping

Structured Troubleshooting Procedure

By combining the previously mentioned Three-step troubleshooting procedure and the subprocesses of Problem Diagnosis steps you get

  1. Problem Report
  2. Collect Information
  3. Examine Collected Information
  4. Eliminate Potential Causes
  5. Hypothesize Underlying Cause
  6. Verify Hypothesize
  7. Problem resolution

Problem Report

  • Often lacks information
  • Are you authorized to resolve the problem or need to forward it.
  • Interview the user who reported the problem.

Collect Information

  • Collect information from routers and switches... (show debug commands, log, NMS etc)

Examine Collected information

  • Identify indicators pointing to the underlying cause of the problem
  • Find evidence that can be used to eliminate potential causes

Fin a balance between

  • What is occurring on the network?
  • What should be occurring on the network?

Eliminate Potential Causes

  • Is OSPF running etc.

Hypothesize Underlying Cause

  • If problem can't be resolved (Lack of authority, devices) a temporary fix could resolve the problem here and now.

Verify Hypothesis

  • Implementing the fix. (Make a plan)

Problem resolution

  • Document the resolved problem.

Including Troubleshooting in Routine Network Maintenance

  • Keep documentation up to date and reliable

Maintaining Network Documentation

  • Require documentation - Make documentation a component in the troubleshooting flow. (get used to documenting)
  • Schedule documentation checks - Routinely verify documentation.
  • Automate documentation - Any configuration change on a device should be reflected in the documentation. (Compare)

Establish a baseline

R1#<input>show processes cpu sorted 5min</input>
CPU utilization for five seconds: 5%/0%; one minute: 5%; five minutes: 5%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
 112     3719202   1028129       3617  0.15%  0.13%  0.15%   0 HRPC qos request
   4     2111767    304796       6928  0.00%  0.09%  0.06%   0 Check heaps
 139         232       304        763  0.15%  0.11%  0.05%   2 Virtual Exec
 142      554927   2283402        243  0.15%  0.10%  0.05%   0 IP Input
  34       57731  47158926          1  0.00%  0.02%  0.00%   0 RedEarth Tx Mana
   7      637306   3220477        197  0.15%  0.03%  0.00%   0 ARP Input
   6           0         2          0  0.00%  0.00%  0.00%   0 Timers
<notice> Output omitted... </notice>

Communicating throughout the Troubleshooting Process

Communicating throughout the Troubleshooting Process
Step Description
Problem Report When a user report a problem. Communicate with the user to clarify the problem.
Collect Information Collect information from for example a Service Provider. require communication.
Examine Collected Information Communicate with other IT-staff
Eliminate Potential causes Perhaps the troubleshooter communicate with a consultant.
Hypothesize Underlying Cause The communication with other IT-staff helps to clarify the underlying problem.
Verify Hypothesis Before making online network changes causing outlets. Notify users about the interruption.
Problem Resolution The user reporting the problem should be informed and the user confirm that the problem is resolved.

Change Management

The process of Change Management includes using policies that dictate rules regarding how and when a change can be made and how that change is documented.