Network Troubleshooting Checklist

Define the symptom first

• Is the server completely unreachable or is only one application failing?
• Does the problem affect IPv4, IPv6 or both?
• Is the problem continuous or intermittent?
• Does it affect every remote destination or only one network?

Collect endpoint evidence

• Record the affected source and destination IPs.
• Record the exact timestamp and timezone.
• Record the protocol and port for application-specific failures.
• Repeat the test from another source when possible.

Run basic path tests

ping -c 20 destination-ip
traceroute destination-ip
# If mtr is installed:
mtr -rwzc 100 destination-ip

Test the application port separately

A reachable IP does not prove that the application port is open, and an unreachable application does not prove the network path is down. Test the port independently where appropriate.

nc -vz destination-ip 443

Avoid misleading conclusions

A single speed-test server or a single traceroute is not enough to prove a provider-wide fault. Routing can be asymmetric and remote systems can be congested or rate-limited.

Escalate with a reproducible case

Open a WHMCS support ticket with the evidence above. Clear timestamps, endpoints and repeated tests make provider-side flow, routing and host checks substantially faster.