- Methodology
- Identify the problem
- Gather information
- Identify symptoms
- Question users
- Change management logs
- Duplicate the problem
- Multiple problems?
- Establish a theory of cause
- Refer to the OSI model. Start at the bottom, top or middle. Whichever makes the most sense based on the symptoms.
- 7 Application Layer
- 6 Presentation Layer
- 5 Session Layer
- 4 Transport Layer
- 3 Network Layer
- 2 Data Link Layer
- 1 Physical Layer
- Test the theory
- Avoid breaking network
- Escalate, if your theory does not work.
- Establish a plan of action
- Assuming you’ve identified the problem, the theory of cause appears accurate and the test of the theory went well, create a plan of action.
- Examine the required changes. Consider effects across the network.
- Use the formal change management process for implementing the change.
- Create a rollback plan.
- Implement a solution
- Verify solution
- Ask the user if they’re now able to perform the task.
- Document solution
- If, after iterating through this methodology, the problem hasn’t been solved, start over.
- CLI Utilities: Packet Internet Groper (Ping), ARP, and Route.
- Test if a device is online and able to respond to ICMP
ping <ip-address>- Show the routing table:
ip r- Display the kernel’s IPv4 network neighbour cache:
arp -a- Traceroute: show the routers the traffic passes through on the way to destination.
traceroute <ip-address-or-domain-name>- Investigate sockets:
ss