26. Network troubleshooting ‐ Step by Step how to troubleshoot user complaining Application is down. - SanjeevOCI/Ocidocs GitHub Wiki

Network troubleshooting - Step by Step how to troubleshoot user complaining Application is down.

  1. Get the Source IP and port from the user. Also the destination IP

  2. Give the user Telnet command and ask for the Telnet command output.

  3. Validate if the instance is up or not.

  4. Validate instance belongs to which subnet

  5. Validate if the Network Ingress rule is allowed for the Source CIDR and port combination

  6. Validate Egress rule to ensure that destination is set to all or not, OR the particular IP range is there or not

  7. Check if Server Firewall is ACTIVE in Destination Instance.

systemctl status firewalld

  1. If it is active, check the firewall configuration to ensure that the necessary port/protocol are open.

firewall-cmd --list-all

  1. If the Port is not not, allow it using:

firewall-cmd --zone=public --add-port=<port_number>/tcp firewall-cmd --permanent --zone=public --add-port=<port_number>/tcp

  1. If the firewall configuration is correct, check whether the application is listening on the required port.

netstat -plan| grep -i <port_number>

If the application is NOT listening on the required port, report the issue to the application team.

If the application is listening on the required port, There is no network issue. It is an application issue.

  1. Ask the original user to validate the application and show to us if the application is not running.

  2. If the user shows that application is not running, ask some other user to check if they can access the application. If they are able to access, check in user's system for firewall which is not allowing access to the specific port.