Oracle监听日志频繁报unknown connect data 12537错误诊断

数据库巡检，发现监听日志中频繁报出如下错误

Mon Mar 13 14:52:11 201713-MAR-2017 14:52:11 * <unknown connect data> * 12537TNS-12537: TNS:connection closed TNS-12560: TNS:protocol adapter error  TNS-00507: Connection closed

在此期间，数据库及应用都没有任何异常。

在MOS中找到一篇文档解释这个现象：
Listener Log Intermittently Reports: and either * 12537 or * 12569 errors (文档 ID 1664901.1)

节选重要信息如下：

结论：

These errors are not caused by an Oracle product, but are most likely caused by a 3rd party tool.  

原因：

What is happening is something, such as a 3rd party probe, is trying to connect to the listener, but the listener does not understand this connection because it is NOT a sqlnet connection.  It knows this because sqlnet uses a unique header to identify itself.  

复现方法

After 60 seconds, the listener will give up trying to identify this connection and report a TNS-12525 error.However, if the unknown connection attempt is terminated BEFORE the 60 seconds, then you get the error in the listener log: * <unknown connect data> * 12537TNS-12537: TNS:connection closedTNS-12560: TNS:protocol adapter errorTNS-00507: Connection closed <possible OS error here>Reproducing the error is easy:On the server, simply ssh to yourself on the listener port.For example: ssh -p 1521 oracle@listener_hostnameIf you kill this command after a few seconds with CTRL-C, check the appropriate listener log to see the error.

根据文档上提供的复现该问题的方法，测试了一下，成功复现出了相同的错误信息。