Most Common Reason for ORA-3136 WARNING : Inbound Connection Timed Out

The most common reason for warning message in alert log is when an user gets error at connect time, ORA-01017 invalid username /password , and on the same prompt, if no update is made for 1 minute(default) then the alert loggets WARNING: inbound connection timed out (ORA-3136)

To reproduce the issue try the following steps:

Place the below parameter in the sqlnet.ora of the server (this is the default value of the parameter)

=======================================================
SQLNET.INBOUND_CONNECT_TIMEOUT=60
=======================================================


Make the tnsnames entry on the server with dedicated as server like
=======================================================
orcl10203=
(DESCRIPTION=
(ADDRESS=(HOST=testnet.idc.oracle.com)(PORT=1521)(PROTOCOL=TCP))
(CONNECT_DATA=
(SERVER=DEDICATED)
(SERVICE_NAME=orcl10203)
)
)
=======================================================


Now open a sqlplus session and enter wrong username or password:
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[oracle@testnet admin]$ sqlplus system/jkkdsf@orcl10203

SQL*Plus: Release 10.2.0.3.0 - Production on Thu Mar 19 17:51:35 2009

Copyright (c) 1982, 2006, Oracle. All Rights Reserved.

ERROR:
ORA-01017: invalid username/password; logon denied
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Keep the sqlplus session open for 60 seconds and in the alert log after 60th second , you will notice ORA-3136
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$tail -f alert_orcl10203.log
Thu Mar 19 17:52:36 2009
WARNING: inbound connection timed out (ORA-3136)
=======================================================


In the server sqlnet tracing you would see following :
=======================================================
[19-MAR-2009 17:52:36:865] ntt2err: entry
[19-MAR-2009 17:52:36:865] ntt2err: soc 1660 error - operation=5, ntresnt[0]=522, ntresnt[1]=4, ntresnt[2]=0
[19-MAR-2009 17:52:36:865] ntt2err: exit
[19-MAR-2009 17:52:36:865] ntt2err: entry
[19-MAR-2009 17:52:36:865] ntt2err: soc 1660 error - operation=5, ntresnt[0]=530, ntresnt[1]=38, ntresnt[2]=0
[19-MAR-2009 17:52:36:865] ntt2err: exit
=======================================================