1、清空存在的策略

当你开始创建新的策略，你可能想清除所有的默认策略，和存在的策略，可以这么做：

iptables -F  或者iptables –flush

2、设置默认策略

默认链策略是ACCEPT，改变所有的链策略为DROP:

iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP

3、阻止一个指定的ip

BLOCK_THIS_IP=“x.x.x.x"
iptables -A INPUT -s ”$BLOCK_THIS_IP“ -j DROP
iptables -A INPUT -i eth0 -s "$BLOCK_THIS_IP" -j DROP
iptables -A INPUT -i eth0 -p tcp -s "$BLOCK_THIS_IP" -j DROP

4、允许SSH

允许所有通过eth0接口使用ssh协议连接本机：

iptables -A INPUT -i eth0 -p tcp –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

5、允许某个网段通过ssh连接

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

6、允许http和https

允许所有进来的web流量：http协议80端口，https协议是443端口

iptables -A INPUT -i eth0 -p tcp –dport 80 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 80 -m state –state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp –dport 443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 443 -m state –state ESTABLISHED -j ACCEPT

7、多个策略联合一起

允许ssh，http，https：

iptables -A INPUT -i eth0 -p tcp -m multiport –dports 22,80,443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport –sports 22,80,443 -m state –state ESTABLISHED -j ACCEPT

8、允许SSH连接其他主机

iptables -A OUTPUT -o eth0 -p tcp –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

9、允许SSH连接指定的网段

iptables -A OUTPUT -o eth0 -p tcp -d 192.168.100.0/24 –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

10、允许https出去

iptables -A OUTPUT -o eth0 -p tcp –dport 443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 443 -m state –state ESTABLISHED -j ACCEPT

11、对web请求做负载均衡(每三个包，均衡到指定服务器，需要扩展iptables)

iptables -A PREROUTING -i eth0 -p tcp –dport 443 -m state –state NEW -m nth –counter 0 –every 3 –packet 0 -j DNAT –to-destination 192.168.1.101:443
iptables -A PREROUTING -i eth0 -p tcp –dport 443 -m state –state NEW -m nth –counter 0 –every 3 –packet 1 -j DNAT –to-destination 192.168.1.102:443
iptables -A PREROUTING -i eth0 -p tcp –dport 443 -m state –state NEW -m nth –counter 0 –every 3 –packet 2 -j DNAT –to-destination 192.168.1.103:443

12、允许ping

iptables -A INPUT -p icmp –icmp-type echo-request -j ACCEPT
iptables -A OUTPUT -p icmp –icmp-type echo-reply -j ACCEPT

13、允许ping远程

iptables -A OUTPUT -p icmp –icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp –icmp-type echo-reply -j ACCEPT

14、允许本地回环

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

15、允许内网访问外部网络

这个例子eth1 连接外部网络，eth0连接内部网络

iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT

16、允许DNS出去

iptables -A OUTPUT -p udp -o eth0 –dport 53 -j ACCEPT
iptables -A INPUT -p udp -i eth0 –sport 53 -j ACCEPT

17、允许NIS连接

NIS端口是动态的，当ypbind启动时它分配端口。

首先运行 rpcinfo -p 显示得到端口号，这个例子使用端口850,853。

iptables -A INPUT -p tcp –dport 111 -j ACCEPT
iptables -A INPUT -p udp –dport 111 -j ACCEPT
iptables -A INPUT -p tcp –dport 853 -j ACCEPT
iptables -A INPUT -p udp –dport 853 -j ACCEPT
iptables -A INPUT -p tcp –dport 850 -j ACCEPT
iptables -A INPUT -p udp –dport 850 -j ACCEPT

上面的例子当ypbind重新启动时将失效，有2种解决方案：

(1) 分配nis服务静态ip

(2) 使用精妙的脚本

18、允许指定网段连接Rsync

iptables -A INPUT -i eth0 -p tcp -s 192.168.101.0/24 –dport 873 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 873 -m state –state ESTABLISHED -j ACCEPT

19、允许mysql从指定的网段连接

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 –dport 3306 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 3306 -m state –state ESTABLISHED -j ACCEPT

20、允许sendmail或者postfix

iptables -A INPUT -i eth0 -p tcp –dport 25 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 25 -m state –state ESTABLISHED -j ACCEPT

21、允许IMAP和IMAPS

iptables -A INPUT -i eth0 -p tcp –dport 143 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 143 -m state –state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp –dport 993 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 993 -m state –state ESTABLISHED -j ACCEPT

22、允许POP3和POP3S

iptables -A INPUT -i eth0 -p tcp –dport 110 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 110 -m state –state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp –dport 995 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 995 -m state –state ESTABLISHED -j ACCEPT

23、预防DDOS攻击

iptables -A INPUT -p tcp –dport 80 -m limit –limit 25/minute –limit-burst 100 -j ACCEPT
-m ：使用iptables扩展
–limit 25/minute : 限制分钟连接请求数
–limit-burst：触发阀值，一次涌入数据包数量

24、端口转发

来自442的都转到22端口

iptables -t nat -A PREROUTING -p tcp -d 192.168.102.37 –dport 422 -j DNAT –to 192.168.102.37:22

你还必须明确允许442端口

iptables -A INPUT -i eth0 -p tcp –dport 422 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 422 -m state –state ESTABLISHED -j ACCEPT

25、包丢弃日志

你也许想查看所有丢弃包的日志。首先创建一个新链叫 LOGGING

iptables -N LOGGING

确保所有的连接跳到LOGGING

iptables -A INPUT -j LOGGING

记录这些包通过自定义名字 "log-prefix"

iptables -A LOGGING -m limit –limit 2/min -j LOG –log-prefix "IPTables Packet Dropped:" –log-level 7

最后丢弃这些数据包

iptables -A LOGGING -j DROP