2461656 - R3trans shows DB connection error even DB is up and running

If a SAP system fails to startup, the administrators will usually run command R3trans -d at the application host firstly to test whether the connection to database works well. If the connection works well, R3trans will show the following inforamtion in the console.

>R3trans -d
This is R3trans version 6.25 (release 745 - 20.12.16 - 20:16:08).
unicode enabled version
R3trans finished (0000).

But sometimes R3trans could show the following network connection error in its log trans.log even the database is up and running. This KBA will show the troubleshooting guide for this situation

SQLERRTEXT : Connection failed (RTE:[89006] System call 'connect' failed, rc=111:Connection refused)
***LOG BY0=>Connection failed (RTE:[89006] System call 'connect' failed, rc=111:Connection refused)

NOTICE: the error for the connect system call is returned by OS, and the error number and text could be different. For example, "113  No route to host". For Linux/Unix system, please see man connect for more inforamtion.

network; unable to start , KBA , BC-NET , Obsolete - Formerly used for network tests , HAN-DB , SAP HANA Database , BC-CST , Client/Server Technology , BC-DB , Database Interface, Database Platforms , How To