🛠️ Network Troubleshooting Methodology (Section 1.4)

1. Identify the Problem

Gather Information (scope/location), Question Users (open/closed questions), identify symptoms, and determine what has changed (or if it never worked).

Scope of the Problem

The area or number of systems affected. Helps determine priority and identify the source.

OSI Model Troubleshooting Approach

Start from Layer 1 (Bottom-to-Top) or Layer 7 (Top-to-Bottom), ruling out each layer before moving to the next.

Divide and Conquer Approach

Start with the layer most likely to be causing the problem, then work up or down based on test results.

2. Establish a Theory of Probable Cause

Question the obvious (e.g., is the cable plugged in?). Use methodical approaches like the OSI model or Divide and Conquer.

3. Test the Theory to Determine Cause

Use diagnostic tools to prove or disprove the theory. If unconfirmed, establish a new theory or escalate the problem.

Escalation (When is it required?)

Problem is beyond your knowledge, falls under a warranty, requires major reconfiguration, or the customer becomes difficult.

4. Establish a Plan of Action

Determine the best solution: Repair, Replace (often using a known good substitute), or Accept (find a workaround). Must assess potential effects.

5. Implement the Solution

Follow the change management plan. Back up data and configuration before starting, and test after each change.

Key Implementation Safety Procedure

If a change fails, reverse the change immediately before trying something else, to avoid compounding the problem.

6. Verify Full System Functionality

Validate the fix resolves the reported problem, ensure the entire system functions normally, and gain customer acceptance.

Preventive Measures

Actions taken during verification to eliminate factors that may cause recurrence (e.g., clear labeling, implementing failover/redundancy).

7. Document Findings

The final step: Record the symptoms, actions taken, outcomes, and lessons learned for future reference.