FREE TROUBLESHOOTING GUIDE
Network troubleshooting: evidence before guessing
Use a repeatable workflow from the physical layer upward.
1 · Define scope
One user, one VLAN, one site or everyone? Identify what changed and when.
2 · Physical & link
Power, cable, optics, link LEDs, interface state, errors and negotiated speed.
3 · Addressing
Verify IP address, prefix, default gateway and DHCP lease. Watch for APIPA or duplicate addressing.
4 · Local reachability
Test loopback, local interface and default gateway before remote destinations.
5 · Routing
Inspect the route table and path. Determine where forwarding stops.
6 · DNS
If IP connectivity works but names fail, inspect resolver configuration and DNS responses.
7 · Service & ports
Confirm the application is listening and ACL/firewall policy allows the required traffic.
8 · Document
Record symptoms, evidence, root cause, fix and verification so the solution becomes reusable knowledge.
Useful commands: ipconfig /all · ping · tracert/traceroute · nslookup/dig · ip addr · ip route · ss · arp/ip neigh