新裝的centos6.3+db29.7，數據庫導入完了的之后用Toad連接訪問之的時候出錯了。
DB2 Database Error: ERROR [08001] [IBM] SQL30081N A communication error has been detected. Communication protocol being used: "TCP/IP". Communication API being used: "SOCKETS". Location where the error was detected: "10.20.51.155". Communication function detecting the error: "selectForConnectTimeout". Protocol specific error code(s): "0", "*", "*". SQLSTATE=08001 (Remembered answer: "OK". Enable)
查了好久，網上給了各種解釋，其中有個人提到了可能與防火牆有關。
一開始我的做法很黃，就是把防火牆關了，連接下就能連上了。
$ service iptables stop
現在覺得需要添加規則，研究了下iptables相關命令。得出
[root@localhost ~]# iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 50000 -j ACCEPT
[root@localhost ~]# /etc/rc.d/init.d/iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables:[ OK ]
[root@localhost ~]# service iptables restart
iptables: Flushing firewall rules: [ OK ]
iptables: Setting chains to policy ACCEPT: filter [ OK ]
iptables: Unloading modules: [ OK ]
iptables: Applying firewall rules: [ OK ]
再次嘗試用客戶端連接，依然報錯。查看下：
[root@localhost ~]# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
2 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0
3 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
4 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
5 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
6 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:50000
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
1 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
原因猜測是優先順序問題，在我們新規則之前有一個reject all，他禁止了對地發包的訪問。
查詢了下對應方法，發現我參數 iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 50000 -j ACCEPT
改成 iptables -I INPUT -m state --state NEW -m tcp -p tcp --dport 50000 -j ACCEPT，應該可以實現
*-A是插入規則到末尾，-I是插入到頂部
把剛剛的規則刪除：
[root@localhost ~]# iptables -D INPUT 6
[root@localhost ~]# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
2 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0
3 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
4 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
5 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
1 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
刪除成功，從新追加：
[root@localhost ~]# iptables -I INPUT -m state --state NEW -m tcp -p tcp --dport 50000 -j ACCEPT
[root@localhost ~]# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:50000
2 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0
4 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
5 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
6 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
1 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
再次嘗試連接，OK連上了。
這個時候要記得保存剛剛的更改。不然下次service iptables restart事件發生的話，那么此次設置無效，連接失敗。
[root@localhost ~]# /etc/rc.d/init.d/iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables:[ OK ]
[root@localhost ~]# service iptables restart
iptables: Flushing firewall rules: [ OK ]
iptables: Setting chains to policy ACCEPT: filter [ OK ]
iptables: Unloading modules: [ OK ]
iptables: Applying firewall rules: [ OK ]
[root@localhost ~]# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:50000
2 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0
4 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
5 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
6 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
1 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
到此結束。