DCNSA Level III
Network Troubleshooting cheat sheet
Every chapter's key points, formulas and definitions on one page, for the last week before the exam. Each heading links to the chapter that explains it.
Common network issues
- Diagnose in order from the quickest, most local check to the most involved: hardware, ipconfig, ping and tracert, a DNS check, the ISP, malware, then the system logs.
- A large share of reported faults are a loose or unplugged cable, which is why the hardware is checked before any software or configuration theory.
- When a ping to an external IP address succeeds but the same destination fails by name, the fault is isolated to DNS, and nslookup confirms it.
- A fault passes through four stages before it can be fixed: reporting, detection, classification and location.
- Isolate the problem by ruling out what works rather than replacing parts speculatively, and close a fault only once testing shows the original symptom is gone and nothing new has broken.
Key terms
- Fault reporting
- Recording the fault, when it started, its symptoms and who is affected, the starting point for any investigation and the record a technician returns to if the first theory turns out wrong.
- Fault detection
- Identifying that a fault exists at all, sometimes before a user even reports it, through monitoring (the maintenance schedule in Network Operating Systems) that catches a problem developing before it becomes a full outage.
- Fault classification
- Categorising the fault by type (hardware, software, configuration, external) and severity, to prioritise it correctly against other work and route it to the right person or team.
- Fault location
- Narrowing down exactly where in the network the fault originates, the specific device, link or configuration setting responsible, which is what the diagnostic procedure above is actually for.
The rest of the sheet covers
- Resolving network issues
- Documenting a network
- Exam technique and revision
- Glossary