"An existing connection was forcibly closed by the remote host" errors for Oracle within 0ms of authentication (4310073)

The Oracle agent raises connection availability alarms immediately (within 0ms) after attempting to connect to the Oracle host. The error message indicates a failure to establish an Oracle JDBC connection due to the remote host forcibly closing the connection:

The connection to the instance XXX failed. Failed to establish a Oracle JDBC connection protocol to Host [HOSTNAME], user account [sys]. Reason: [IO Error: An existing connection was forcibly closed by the remote host, Authentication lapse 0 ms.- Profile:OracleProfile{host='HOSTNAME', service='service_name', username='sys', asSysDBA=true, ports='1521', useSSL=false, properties={oracle.jdbc.ReadTimeout=900000}}]. . [Oracle Error Code = 17002. SQL state : 08006]

This issue typically results from network access restrictions, incorrect listener or Oracle network configuration, or issues with SSL/TLS settings on the Oracle database side.

1. Verify Oracle Security Group Configuration
   Ensure the security group (firewall rules, network ACLs) correctly permits access to the Oracle instance and database.

2. Check sqlnet.ora for Valid Node Checking
   Locate the sqlnet.ora file and verify if tcp.validnode_checking is set to yes. This feature restricts connections to specific IP addresses. To allow connections, set:

    

   tcp.validnode_checking = no

   Then restart the Oracle listener.

3. Use SID Instead of Service Name
   Modify the connection settings to use the SID instead of the service name to establish the connection.

4. Review Oracle Listener Logs
   Examine the listener log for any errors and resolve the issues identified.

5. Verify SQLNET Encryption Settings
   Check if the parameter SQLNET.IGNORE_ANO_ENCRYPTION_FOR_TCPS is set to TRUE in the database configuration. JDBC connections do not support double encryption. Disable this setting or avoid combining TLS encryption with Oracle native encryption.

6. Forced SSL and Data Guard Issues
   Workaround
   When Oracle databases are configured to force SSL, Data Guard connections using SSL may fail. Contact Quest Support for a hotfix if this applies to your environment.
   Status
   This issue is tracked under Defect ID FOG-5260 and has been addressed in Oracle cartridge versions 6.3 and later.