Q: Oracle connections problem We are currently seeing the following error in our Oracle listener log. There are thousands of these errors in there
TNS-12502: TNS:listener received no CONNECT_DATA from client
We connect to this oracle 10g database from an app running on Websphere 6.1
Any ideas what could be causing this error or any suggestions in order to fix it?
Thanks
Damien

A: You can get this if a process is quickly opening and closing the network port the listener is using (e.g. 1521). It could be a runaway process or a port sniffer.

A: Which driver are you using. This exception generally means that the connect request did not specify a service.
if you are using the native driver (type2) or JDBC-ODBC Bridge (type 1) then look in your tnsnames.ora file and insure that the SERVICE_NAME property is set.
LOCALNAME =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = servername)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = servicename)
    )
  )

If you are using the thin driver (type 4) then make sure that the connection string has the service name.
jdbc:oracle:thin:@servername:1521:servicename


A: that's mean your TNSlistener is not running.
you can check whether the listener is on or not using Tnsping 
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