Starting Oracle Listener Tracing    March 25 2008

The classical way is to set the following listener.ora parameters and reload:

TRACE_FILE_LISTENER=listener.trc (listener.trc is the default)


What i was missing is that you can initiate tracing by issuing the following command   

lsnrctl trace 16 (to turn the trace on)
lsnrctl trace off (to turn the trace off)


the trace information is generated in the default trace directory that can be found at $ORACLE_HOME/network/trace