为什么会出现这样的情况呢？网上搜索后得知，在Oracle11G中，有这样两个参数SQLNET.INBOUND_CONNECT_TIMEOUT 和INBOUND_CONNECT_TIMEOUT_listenername；他们的默认值为60s，这两个参数负责登陆用户与服务器验证的超时时间，在10GR2以前的版本默认是0s，为了防止Denial of Service (DOS)攻击，在以后的版本中才设置为60s。如果在登录过程中，服务器没有给出及时的响应，那么将会在60后给出错误提示，这个超时时间显然有点过长，导致用户重复登陆的频率加大，频繁的登录引起数据库负载过大。解决问题：减少着两个参数的超时时间，把它们分别设为3和2s。Metalink上给出的解决方案如下: 1. set INBOUND_CONNECT_TIMEOUT_=0 in listener.ora 2. set SQLNET.INBOUND_CONNECT_TIMEOUT = 0 in sqlnet.ora of server. 3. stop and start both listener and database. 4. Now try to connect to DB and observe the behaviour以下是Oracle官方文档的一段： SQLNET.INBOUND_CONNECT_TIMEOUT Use the SQLNET.INBOUND_CONNECT_TIMEOUT parameter to specify the time, in seconds, for a client to connect with the database server and provide the necessary authentication information.If the client fails to establish a connection and complete authentication in the time specified, then the database server terminates the connection. In addition, the database server logs the IP address of the client and an ORA-12170: TNS:Connect timeout occurred error message to the sqlnet.log file. The client receives either an ORA-12547: TNS:lost contact or an ORA-12637: Packet receive failed error message.Without this parameter, a client connection to the database server can stay open indefinitely without authentication.Connections without authentication can introduce possible denial-of-service attacks, whereby malicious clients attempt to flood database servers with connect requests that consume resources.To protect both the database server and the listener, Oracle Corporation recommends setting this parameter in combination with the INBOUND_CONNECT_TIMEOUT_listener_name parameter in the listener.ora file. When specifying values for these parameters, consider the following recommendations:Set both parameters to an initial low value. Set the value of the INBOUND_CONNECT_TIMEOUT_listener_name parameter to a lower value than theSQLNET.INBOUND_CONNECT_TIMEOUT parameter. For example, you can set INBOUND_CONNECT_TIMEOUT_listener_name to 2 seconds and INBOUND_CONNECT_TIMEOUT parameter to 3 seconds. If clients are unable to complete connections within the specified time due to system or network delays that are normal for the particular environment, then increment the time as needed.修改listener的inbound_connect_timeout参数的方法SET INBOUND_CONNECT_TIMEOUT PurposeUse thede>SETde>de>INBUND_CONNECT_TIMEOUTde>command to specify the time, in seconds, for the client to complete its connect request to the listener after the network connection had been established.If the listener does not receive the client request in the time specified, then it terminates the connection. In addition, the listener logs the IP address of the client and ande>ORA-12525:TNS: listener has not received client's request in time allowedde>error message to thede>listener.logde>file.See Also:Oracle Database Net Services Administrator's Guidefor information about specifying the time-out for client connections SyntaxFrom the Listener Control utility:LSNRCTL> SET INCOUND_CONNECT_TIMEOUTArgumentsde>{de>de>timede>de>}de>: Specify the time, in seconds. Default setting is 60 seconds.ExampleLSNRCTL> SET INBOUND_CONNECT_TIMEOUT 2Connecting to (ADDRESS=(PROTOCOL=TCP)(HOST=sales-server)(PORT=1521))LISTENER parameter "inbound_connect_timeout" set to 2The command completed successfully.方法一: $ lsnrctlLSNRCTL for IBM/AIX RISC System/6000: Version 10.2.0.3.0 - Production on 29-OCT-2007 10:00:57Copyright (c) 1991, 2006, Oracle. All rights reserved.Welcome to LSNRCTL, type "help" for information.LSNRCTL> help The following operations are available An asterisk (*) denotes a modifier or extended command:start stop status services version reload save_config trace spawn change_password quit exit set* show* LSNRCTL> show The following operations are available after show An asterisk (*) denotes a modifier or extended command:rawmode displaymode rules trc_file trc_directory trc_level log_file log_directory log_status current_listener inbound_connect_timeout startup_waittime snmp_visible save_config_on_stop dynamic_registration LSNRCTL> show inbound_connect_timeout Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521)) LISTENER parameter "inbound_connect_timeout" set to 60 The command completed successfullyLSNRCTL> set inbound_connect_timeout 0 Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521)) LISTENER parameter "inbound_connect_timeout" set to 0 The command completed successfullyLSNRCTL> show inbound_connect_timeout Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521)) LISTENER parameter "inbound_connect_timeout" set to 0 The command completed successfullyLSNRCTL> set save_config_on_stop on #表示修改参数永久生效，否则只是临时生效，下次重启监听又还原为原来的值了LSNRCTL> exit 方法二： 修改listener.ora文件，加入: INBOUND_CONNECT_TIMEOUT_LISTENER_NAME=0参考文档：inbound connection timed out (ORA-3136)错误诊断：http://blog.chinaunix.net/u1/50863/showart_410003.htmlORACLE 帮助文件
不会的，1521是oracle服务器上的，不会关闭，我觉得有可能是访问的客户端的防护软件（比如杀毒软件，卡巴斯基等）禁止你访问吧！
1. set INBOUND_CONNECT_TIMEOUT_=0 in listener.ora
2. set SQLNET.INBOUND_CONNECT_TIMEOUT = 0 in sqlnet.ora of server.
3. stop and start both listener and database.
4. Now try to connect to DB and observe the behaviour以下是Oracle官方文档的一段：
SQLNET.INBOUND_CONNECT_TIMEOUT
Use the SQLNET.INBOUND_CONNECT_TIMEOUT parameter to specify the time, in seconds, for a client to connect with the database server and provide the necessary authentication information.If the client fails to establish a connection and complete authentication in the time specified, then the database server terminates the connection. In addition, the database server logs the IP address of the client and an ORA-12170: TNS:Connect timeout occurred error message to the sqlnet.log file. The client receives either an ORA-12547: TNS:lost contact or an ORA-12637: Packet receive failed error message.Without this parameter, a client connection to the database server can stay open indefinitely without authentication.Connections without authentication can introduce possible denial-of-service attacks, whereby malicious clients attempt to flood database servers with connect requests that consume resources.To protect both the database server and the listener, Oracle Corporation recommends setting this parameter in combination with the INBOUND_CONNECT_TIMEOUT_listener_name parameter in the listener.ora file. When specifying values for these parameters, consider the following recommendations:Set both parameters to an initial low value.
Set the value of the INBOUND_CONNECT_TIMEOUT_listener_name parameter to a lower value than theSQLNET.INBOUND_CONNECT_TIMEOUT parameter.
For example, you can set INBOUND_CONNECT_TIMEOUT_listener_name to 2 seconds and INBOUND_CONNECT_TIMEOUT parameter to 3 seconds. If clients are unable to complete connections within the specified time due to system or network delays that are normal for the particular environment, then increment the time as needed.修改listener的inbound_connect_timeout参数的方法SET INBOUND_CONNECT_TIMEOUT
PurposeUse thede>SETde>de>INBUND_CONNECT_TIMEOUTde>command to specify the time, in seconds, for the client to complete its connect request to the listener after the network connection had been established.If the listener does not receive the client request in the time specified, then it terminates the connection. In addition, the listener logs the IP address of the client and ande>ORA-12525:TNS: listener has not received client's request in time allowedde>error message to thede>listener.logde>file.See Also:Oracle Database Net Services Administrator's Guidefor information about specifying the time-out for client connections
SyntaxFrom the Listener Control utility:LSNRCTL> SET INCOUND_CONNECT_TIMEOUTArgumentsde>{de>de>timede>de>}de>: Specify the time, in seconds. Default setting is 60 seconds.ExampleLSNRCTL> SET INBOUND_CONNECT_TIMEOUT 2Connecting to (ADDRESS=(PROTOCOL=TCP)(HOST=sales-server)(PORT=1521))LISTENER parameter "inbound_connect_timeout" set to 2The command completed successfully.方法一:
$ lsnrctlLSNRCTL for IBM/AIX RISC System/6000: Version 10.2.0.3.0 - Production on 29-OCT-2007 10:00:57Copyright (c) 1991, 2006, Oracle. All rights reserved.Welcome to LSNRCTL, type "help" for information.LSNRCTL> help
The following operations are available
An asterisk (*) denotes a modifier or extended command:start stop status
services version reload
save_config trace spawn
change_password quit exit
set* show* LSNRCTL> show
The following operations are available after show
An asterisk (*) denotes a modifier or extended command:rawmode displaymode
rules trc_file
trc_directory trc_level
log_file log_directory
log_status current_listener
inbound_connect_timeout startup_waittime
snmp_visible save_config_on_stop
dynamic_registration LSNRCTL> show inbound_connect_timeout
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
LISTENER parameter "inbound_connect_timeout" set to 60
The command completed successfullyLSNRCTL> set inbound_connect_timeout 0
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
LISTENER parameter "inbound_connect_timeout" set to 0
The command completed successfullyLSNRCTL> show inbound_connect_timeout
Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=1521))
LISTENER parameter "inbound_connect_timeout" set to 0
The command completed successfullyLSNRCTL> set save_config_on_stop on #表示修改参数永久生效，否则只是临时生效，下次重启监听又还原为原来的值了LSNRCTL> exit
方法二：
修改listener.ora文件，加入: INBOUND_CONNECT_TIMEOUT_LISTENER_NAME=0参考文档：inbound connection timed out (ORA-3136)错误诊断：http://blog.chinaunix.net/u1/50863/showart_410003.htmlORACLE 帮助文件