In order to properly and rapidly identify the affected areas of the network, you should make use of good mapping tools, including:
- Packet sniffers (like Wireshark)
- Detailed topology diagrams (both physical and logical)
- Other schematics of the network
You need to understand the physical and logical network topology in order to identify the affected areas and trace the problem throughout the network. In addition, you should also be able to use tools like ping, event viewer, and other monitoring tools.
| Note: If the organization uses some kind of security policy, you should also understand this policy as part of the troubleshooting process.
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Solid network documentation helps in this phase, including documentation about IP addressing within the network. Using VLSM and address aggregation will be useful, as they can prevent problems within a network area from affecting the entire routing domain. Using IP addressing aggregation to represent many networks can create problem domains, which will help in the troubleshooting process.
Another part of this phase is understanding which applications, services, and protocols are used by every group of users within the network. Knowing which areas of the organization are using a certain type of application can help to quickly isolate the problem domain and continue the troubleshooting process.
An important thing that helps in this troubleshooting step is designing a modular network that contains multiple layers, such as the following:
- Core Layer
- Distribution Layer
- Access Layer
- Management module
- Remote Access module
- VPN module
If you have WAN connectivity to remote and branch offices, it would help to train remote network operators in the troubleshooting process so they will be able to remotely help from their respective offices. In addition, if the problem includes other technology areas, you should consult with the colleagues responsible for those areas and maybe even form a troubleshooting team in order to fix the problem as soon as possible.
Depending on the situation, to minimize the effect of the problem and shorten the troubleshooting process, you should make sure you have:
- Backups of the system
- Roll-back techniques, especially in situations in which modifying device configurations does not solve the problem
- Spare parts
- Failover between devices and modules.