 Now that we have seen what tools and commands can be used at different layers of computer network, it is time to see heuristics related to troubleshooting a computer network. The first important thing to do is document the current state, let us take a note of what parts of the system are working, which parts are not working, how are the connections made, what access is given to different systems etc. After you do that try to recollect when was the system working correctly as desired and then try to see or recollect if any changes were made after which the system is showing an undesired behavior. Now try to compare this current undesired behavior of the system with the desired behavior of the system and try to narrow down which subsystem might be reason for this undesired behavior.