Have an up-to-date inventory of network devices and connections
Keeping a detailed map of your IT infrastructure allows you to evaluate its robustness, performance and stability. At the same time, you check your maintenance contracts and identify the components that are no longer used but still connected.
Keep this inventory up to date. If there is an incident, it can help you to detect where the problem comes from and potentially which supplier you need to contact. Do you entrust this task to external staff? Don't forget that you need to keep control of the situation.