Network troubleshooting can be overwhelming without a systematic approach. Here’s the methodology I use, learned through my Network+ certification and hands-on experience at the Microsoft Innovation Hub.
The OSI Model Approach
I always work from Layer 1 up:
Layer 1 - Physical
- Cable connections secure?
- Link lights on NIC and switch?
- Correct cable type (straight-through vs crossover)?
- Power to network devices?
Layer 2 - Data Link
- MAC address showing in ARP table?
- VLAN assignment correct?
- Switchport configuration matching (speed/duplex)?
- STP blocking any ports?
Layer 3 - Network
- IP address and subnet mask correct?
- Default gateway reachable?
- Routing table has correct paths?
- No ACLs blocking traffic?
My Troubleshooting Toolkit
Command Line Tools:
ping- Basic connectivitytracert/traceroute- Path analysisipconfig/ifconfig- Interface statusnetstat- Connection statusnslookup/dig- DNS resolution
Physical Tools:
- Cable tester
- Tone generator and probe
- Network analyzer (Wireshark)
Common Issues I’ve Encountered
VLAN Mismatches
Symptom: Device gets IP but can’t reach other subnets Solution: Verify native VLAN matches on both ends of trunk
Duplex Mismatches
Symptom: Slow performance, CRC errors Solution: Set both sides to auto-negotiate or hard-code both
DNS Resolution Failures
Symptom: Can ping IP but not hostname Solution: Check DNS server config, flush DNS cache
Documentation
Always document:
- Symptoms reported
- Tests performed and results
- Changes made
- Final resolution
This systematic approach has helped me resolve issues faster and prevent future occurrences.