在查看alert日志的时候发现：
1 ***********************************************************************
2
3 Fatal NI connect error 12170.
4
5 VERSION INFORMATION:
6 TNS for Linux: Version 11.2.0.1.0 - Production
7 Oracle Bequeath NT Protocol Adapter for Linux: Version 11.2.0.1.0 - Production
8 TCP/IP NT Protocol Adapter for Linux: Version 11.2.0.1.0 - Production
9 Time: 27-DEC-2012 16:17:46
10 Tracing not turned on.
11 Tns error struct:
12 ns main err code: 12535
13
14 TNS-12535: TNS:operation timed out
15 ns secondary err code: 12560
16 nt main err code: 505
17
18 TNS-00505: Operation timed out
19 nt secondary err code: 110
20 nt OS err code: 0
21 Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=xxx.xxx.xxx.xxx)(PORT=xxxx))
22 Thu Dec 27 16:46:44 2012
23
24
25 ***********************************************************************
参考官方说明关于该警告的说明：
Note:465043.1
The "WARING:inbound connection timed out (ORA-3136)" in the
alert log indicates that the client was not able to complete it‘s authentication
within the period of time specified by parameter
SQLNET.INBOUND_CONNECT_TIMEOUT.
You may also witness ORA-12170 without timeout error on the
database sqlnet.log file.This entry would also have the client address which
failed to get authenticated.Some applications or JDBC thin driver applications
may not have these details.
可能的原因：
1、网络攻击，例如：半开连接攻击
Server gets a connection request from a malcious
client which is not supposed to connect to the database,in which case the error
thrown is the correct behavior.You can get the client address for which the
error was thrown via sqlnet log file.
2、Client在default 60秒内没有完成认证
The server receives a valid client connection request but
the client tabkes a long time to authenticate more than the default 60
seconds.
3、DB负载太高
The DB server is heavily loaded due to which it cannot
finish the client logon within the timeout specified.
WANGING:inbound connection timed out (ORA-3136)
解决问题：
其实这个参数跟监听的一个参数有关：SQLNET.INBOUND_CONNECT_TIMEOUT
这个参数从9i开始引入，指定了客户端连接服务器并且提供认证信息的超时时间，如果超过这个时间客户端没有提供正确的认证信息，服务器会自动中止连接请求，同时会记录试图连接的IP地址和ORA-12170：TNS:Connect
timeout occurred错误。
这个参数的引入，主要是防止DoS攻击，恶意攻击者可以通过不停的开启大量连接请求，占用服务器的连接资源，使得服务器无法提供有效服务。在10.2.0.1起，该参数默认设置为60秒。
但是，这个参数的引入也导致了一些相关的Bug。比如：
Bug 5594769 - REMOTE SESSION DROPPED WHEN LOCAL SESSION
SHARED AND INBOUND_CONNECT_TIMEOUT SET
Bug 5249163 - CONNECTS REFUSED BY TNSLSNR EVERY 49 DAYS
FOR INBOUND_CONNEC_TIMEOUT SECONDS
该参数可以通过设置为0来禁用，在服务端：
1)、设置sqlnet.ora文件：SQLNET.INBOUND_CONNECT_TIMEOUT=0；
2)、设置listener.ora文件：INBOUND_CONNECT_TIMEOUT_listenername=0；
3)、然后reload或者重启监听。
说明：这是由于连接超时所产生的问题，在10.2.0.1.0版本中sqlnet.inbound_connect_timeout参数默认为60秒，即如果连接时间超过60秒则提示超时，而在其他版本中这两个参数默认为0，即无限制。
具体操作例子:
----因为之前修改了很多次参数，一直没成功，这次就索性把监听给停掉了----------------
1 [[email protected] admin]$ lsnrctl stop
2
3 LSNRCTL for Linux: Version 11.2.0.1.0 - Production on 27-DEC-2012 22:40:24
4
5 Copyright (c) 1991, 2009, Oracle. All rights reserved.
6
7 Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=xxxx)(PORT=xxxx)))
8 The command completed successfully
----在sqlnet.ora文件中添加SQLNET.INBOUND_CONNECT_TIMEOUT = 0----------
9 [[email protected] admin]$ vi sqlnet.ora
10 # sqlnet.ora Network Configuration File: /u01/app/oracle/product/11.2.0/db_1/network/admin/sqlnet.ora
11 # Generated by Oracle configuration tools.
12
13 NAMES.DIRECTORY_PATH= (TNSNAMES)
14 SQLNET.INBOUND_CONNECT_TIMEOUT = 0
15----在listener.ora文件添加INBOUND_CONNECT_TIMEOUT_listener=0------------
16 [[email protected] admin]$ vi listener.ora
17
18 # listener.ora Network Configuration File: /u01/app/oracle/product/11.2.0/db_1/network/admin/listener.ora
19 # Generated by Oracle configuration tools.
20
21 LISTENER =
22 (DESCRIPTION_LIST =
23 (DESCRIPTION =
24 (ADDRESS = (PROTOCOL = TCP)(HOST = cnbpi)(PORT = xxxx))
25 # (CONNECT_TIMEOUT_LISTENER = 3600) -------该参数在测试中不起作用
26 )
27 )
28 INBOUND_CONNECT_TIMEOUT_listener=0
29
30 [[email protected] admin]$ lsnrctl
31
32 LSNRCTL for Linux: Version 11.2.0.1.0 - Production on 27-DEC-2012 22:42:14
33
34 Copyright (c) 1991, 2009, Oracle. All rights reserved.
35
36 Welcome to LSNRCTL, type "help" for information.
37
-----因为监听已经停止，所以查不出inbound_connect_timeout参数是否修改成功----------------
38 LSNRCTL> show inbound_connect_timeout
39 Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=cnbpi)(PORT=1521)))
40 TNS-12541: TNS:no listener
41 TNS-12560: TNS:protocol adapter error
42 TNS-00511: No listener
43 Linux Error: 111: Connection refused
44 LSNRCTL> set inbound_connect_timeout 0
45 Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=cnbpi)(PORT=1521)))
46 TNS-12541: TNS:no listener
47 TNS-12560: TNS:protocol adapter error
48 TNS-00511: No listener
49 Linux Error: 111: Connection refused
----启动监听-----------------------------------
50 LSNRCTL> start
51 Starting /u01/app/oracle/product/11.2.0/db_1/bin/tnslsnr: please wait...
52
53 TNSLSNR for Linux: Version 11.2.0.1.0 - Production
54 System parameter file is /u01/app/oracle/product/11.2.0/db_1/network/admin/listener.ora
55 Log messages written to /u01/app/oracle/diag/tnslsnr/cnbpi/listener/alert/log.xml
56 Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=cnbpi)(PORT=xxxx)))
57
58 Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=cnbpi)(PORT=xxxx)))
59 STATUS of the LISTENER
60 ------------------------
61 Alias LISTENER
62 Version TNSLSNR for Linux: Version 11.2.0.1.0 - Production
63 Start Date 27-DEC-2012 22:42:37
64 Uptime 0 days 0 hr. 0 min. 0 sec
65 Trace Level off
66 Security ON: Local OS Authentication
67 SNMP OFF
68 Listener Parameter File /u01/app/oracle/product/11.2.0/db_1/network/admin/listener.ora
69 Listener Log File /u01/app/oracle/diag/tnslsnr/cnbpi/listener/alert/log.xml
70 Listening Endpoints Summary...
71 (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=cnbpi)(PORT=xxxx)))
72 The listener supports no services
73 The command completed successfully
----查看inbound_connect_timeout参数已经修改成功，值为0-------------------
74 LSNRCTL> show inbound_connect_timeout
75 Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=xxxx)(PORT=xxxx)))
76 LISTENER parameter "inbound_connect_timeout" set to 0
77 The command completed successfully
-----因为之前在修改中可能是参数设置不对，所以一直没成功，所以用了这种最笨的方法使监听停掉以后再修改，其实只需修改了参数以后再reload一下就可以了。
参考文档：
http://www.cnblogs.com/diyunpeng/archive/2010/11/12.html
http://wenku.baidu.com/view/190df4aad1f34693daef3ee6.html
TNS-12535: TNS:operation timed out、TNS-00505: Operation timed
out