Lesson 5.7: Troubleshooting a network, layer by layer
A method instead of guessing: start from the bottom of the stack and test one layer at a time (link and address, gateway, the wider network, names, the service), so each answer narrows the problem. The same method helps in incidents, because attacks often look like faults. In the lab you work a real-looking ticket ('the intranet doesn't open') from interface to application, prove where it breaks, and find the forgotten change behind it.
18 min
You will learn to
- Apply a bottom-up troubleshooting method
- Test the interface, gateway and internet separately
- Separate name resolution problems from connectivity problems
- Use evidence (change logs) to find the cause
- Explain why troubleshooting skills matter in security
Key terms
- Bottom-up troubleshooting
- Testing the layers in order, from the physical link to the application, so each working layer is ruled out.
- Connectivity
- Whether packets can travel between two hosts at all, usually tested with ping.
- Name resolution
- Turning a name into an address (hosts file, DNS). A common cause of 'it doesn't work' even when connectivity is fine.
- Change management
- Recording, approving and tracking changes to systems, so problems can be traced to their cause.
- Root cause
- The underlying reason for a problem, as opposed to its symptoms.
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