Troubleshooting

Network Troubleshooting Methodology

Identify the problem

Gather information

• Get as many details as possible
• Duplicate the issue, if possible

Question users

• Your best source of details

Identify symptoms

• May be more than a single symptom

Determine if anything has changed

• Who’s in the wiring closet?

Duplicate the problem, if possible

• The issue is much easier to troubleshoot if you can see it happening

Approach multiple problems individually

• Break problems into smaller pieces

Establish a theory of probable cause

Start with the obvious

• Occam’s razor applies

Consider everything

• Even the not-so-obvious
• Examine the problem from the top of the OSI model to the bottom
• And then from the bottom to the top

Divide and conquer

• Break the problem into smaller pieces
• Remove the pieces that don’t apply

Test the theory

Confirm the theory

• Determine next steps to resolve problem

Theory didn’t work?

• Re-establish new theory or escalate
• Call an expert

Create a plan of action

Build the plan

• Correct the issue with a minimum of impact
• Some issues can’t be resolved during production hours

Identify potential effects

• Every plan can go bad
• Have a plan B
• And a plan C

Implement the solution

Try to fix

• Implement during the change control window

Escalate as necessary

• You may need help from a 3rd party

Verify full system functionality

It’s not fixed until it’s really fixed

• The test should be part of your plan
• Have your customer confirm the fix

Implement preventive measures

• Let’s avoid this issue in the future

Document findings

It’s not over until you update the knowledge base

• Important lessons were learned
• Don’t lose valuable knowledge!

Consider a formal database

• Help desk case notes
• Searchable database

Troubleshooting a network

Let’s recap:

Identify the problem:

• Information gathering, identify symptoms, question users, determine if anything has changes

Establish a theory of probable cause

• Question the obvious

Test the theory to determine cause

• Once the theory is confirmed, determine next steps to resolve the problem.
• If theory is not confirmed, re-establish new theory or escalate.

Establish a plan of action to resolve the problem and identify the potential effects

Implement the solution or escalate as necessary

Verify full system functionality and, if applicable, implement preventative measures

Document finding, actions and outcomes