M7: Troubleshoot Network Problems

Cisco Network Addressing and Basic Troubleshooting: Troubleshoot basic network connectivity issues.

3 Major Troubleshooting Approaches

1. Bottom-Up Approach

2. Top-Down Approach

3. Divide-and-Conquer Approach

Bottom-Up Approach

The most common troubleshooting method for beginners and technicians. Steps are 1. check cables, 2. check ports, 3. check link lights, 4. check duplex/speed, 5. check IP addressing, 6. check routing. It is best for physical issues and connectivity failures. Start at Layer 1.

Top-Down Approach

This troubleshooting method is used when the application is failing. Steps are 1. check the application, 2. check the OS, 3. check the network stack. This is best for when web apps not loading, DNS issues, and authentication failures. Start at Layer 7

Divide-and-Conquer Approach

This troubleshooting method is the fastest method for experienced techs. They start in the middle (Layer 3), test connectivity, if ping works → problem is above Layer 3, if ping fails → problem is below Layer 3. It is best for large networks, time-sensitive troubleshooting.

Troubleshooting Mindset

• Don’t assume - verify

• Change one thing at a time

• Document everything

• Reproduce the issue

• Stay calm and systematic

Network Troubleshooting

It is the process of: 1. Identifying the problem, 2. Isolating the cause, 3. Fixing the issue, 4. Verifying the solution, 5. Documenting what happened.

List of Information to Gather for Troubleshooting

• Nature of the Problem

• Equipment Information

• Configuration and Topology

• Previous Troubleshooting Attempts

Nature of Problem

Troubleshooting information about end-user reports, symptoms observed, error messages, when the issue started, whether the issue is intermittent or constant, and whether multiple users are affected.

Equipment Information

Troubleshooting information about what devices are involved. Collect details such as manufacturer, model number, firmware version, OS version, serial number, warranty status, and ownership (internal, vendor-managed, ISP-owned)

Configuration and Topology

Troubleshooting information that tells you how the network is supposed to work before you can fix how it is currently working. This includes physical and logical structure, configuration files, log files, and change history.

Previous Troubleshooting Attempts

Troubleshooting information about if someone already tried to fix the issue, you need to know: what steps were taken, what results were observed, what was ruled out, and whether any temporary fixes were applied.