本文转自 http://www.cnblogs.com/kerrycode/archive/2012/12/14/2818421.html
1：首先检查网络是否能ping通
2：检查TNS配置（TNS配置也没有问题）
GSP =
(DESCRIPTION =
(ADDRESS =(PROTOCOL = TCP)(HOST = 172.20.36.79)(PORT = 1521))
(CONNECT_DATA=
(SERVER = DEDICATED)
(SERVICE_NAME = gsp)
)
)
3：查看服务器监听服务是否启动
[oracle@wgods ~]$ lsnrctl status
LSNRCTL for Linux: Version 10.2.0.1.0 - Production on 14-DEC-2012 15:51:13
Copyright (c) 1991, 2005, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1)))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for Linux: Version 10.2.0.1.0 - Production
Start Date 14-DEC-2012 13:15:28
Uptime 0 days 2 hr. 35 min. 45 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /database/oracle/product/dbhome/network/admin/listener.ora
Listener Log File /database/oracle/product/dbhome/network/log/listener.log
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=wgods)(PORT=1521)))
Services Summary...
Service "PLSExtProc" has 1 instance(s).
Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...
Service "gsp" has 2 instance(s).
Instance "gsp", status UNKNOWN, has 1 handler(s) for this service...
Instance "gsp", status READY, has 1 handler(s) for this service...
Service "gspXDB" has 1 instance(s).
Instance "gsp", status READY, has 1 handler(s) for this service...
Service "gsp_XPT" has 1 instance(s).
Instance "gsp", status READY, has 1 handler(s) for this service...
The command completed successfully
4：使用tnsping命令检查，报TNS-12535: TNS: 操作超时，这时我们可以肯定是防火墙的问题了。
C:Userskerry>tnsping 172.20.32.79
TNS Ping Utility for 32-bit Windows: Version 11.2.0.1.0 - Production on 14-12月-2012 15:47:15
Copyright (c) 1997, 2010, Oracle. All rights reserved.
已使用的参数文件:
E:appkerryproduct11.2.0dbhome_1
etworkadminsqlnet.ora
已使用 EZCONNECT 适配器来解析别名
尝试连接 (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=))(ADDRESS=(PROTOCOL=TCP)(HOST=172.20.32.79)(PORT=1521)))
TNS-12535: TNS: 操作超时
对于防火墙问题，我们可以有两种解决方案：
1：关闭防火墙（这种方案不怎么好，关闭防火墙，会带来许多安全隐患）
[root@wgods ~]# service iptables stop
Flushing firewall rules: [ OK ]
Setting chains to policy ACCEPT: filter [ OK ]
Unloading iptables modules: [ OK ]
2：修改iptables，开放1521端口，允许1521端口被连接
2.1 编辑iptables文件，添加-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 1521 -j ACCEPT记录。
[root@wgods sysconfig]# vi iptables
# Generated by iptables-save v1.3.5 on Fri Dec 14 17:03:58 2012
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [1749:243629]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p esp -j ACCEPT
-A RH-Firewall-1-INPUT -p ah -j ACCEPT
-A RH-Firewall-1-INPUT -d 224.0.0.251 -p udp -m udp --dport 5353 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 21 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 25 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 23 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 1521 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
# Completed on Fri Dec 14 17:03:58 2012
~
~
~
~
~
"iptables" 24L, 1212C written
2.2 重启iptables服务
[root@wgods sysconfig]# service iptables restart
Flushing firewall rules: [ OK ]
Setting chains to policy ACCEPT: filter [ OK ]
Unloading iptables modules: [ OK ]
Applying iptables firewall rules: [ OK ]
Loading additional iptables modules: ip_conntrack_netbios_ns ip_conntrack_ftp [ OK ]
2.3 保存新增的规则，以免下次重启机器后，配置规则失效
[root@wgods sysconfig]# service iptables save
Saving firewall rules to /etc/sysconfig/iptables: [ OK ]
2.4 查看1521端口是否开放，允许连接（见红色部分）
[root@wgods sysconfig]# iptables -L -n
Chain INPUT (policy ACCEPT)
target prot opt source destination
RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy ACCEPT)
target prot opt source destination
RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain RH-Firewall-1-INPUT (2 references)
target prot opt source destination
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 255
ACCEPT esp -- 0.0.0.0/0 0.0.0.0/0
ACCEPT ah -- 0.0.0.0/0 0.0.0.0/0
ACCEPT udp -- 0.0.0.0/0 224.0.0.251 udp dpt:5353
ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:631
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:631
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:21
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:23
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:1521
REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
[root@wgods sysconfig]#
从客户端用PL/SQL Developer连接数据库，问题解决。