花了一下午和一晚上通过http://www.frozentux.net/iptables-tutorial/cn/iptables-tutorial-cn-1.1.19.html这篇文档深入学习了iptables这一有力的包过滤系统，文档最后作者提供了一个脚本来配置iptables，我觉得这个脚本的结构设计的相当棒，这里转载过来并附上自己的理解共以后参考。
#!/bin/sh # # rc.firewall - Initial SIMPLE IP Firewall script for Linux 2.4.x and iptables # # Copyright (C) 2001 Oskar Andreasson <bluefluxATkoffeinDOTnet> # # This program is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; version 2 of the License. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # # You should have received a copy of the GNU General Public License # along with this program or from the site that you downloaded it # from; if not, write to the Free Software Foundation, Inc., 59 Temple # Place, Suite 330, Boston, MA 02111-1307 USA # ########################################################################### # # 1. Configuration options. # # # 1.1 Internet Configuration. #定义网络参数变量 # INET_IP="194.236.50.155" INET_IFACE="eth0" INET_BROADCAST="194.236.50.255" # # 1.1.1 DHCP # # # 1.1.2 PPPoE # # # 1.2 Local Area Network configuration. # # your LAN's IP range and localhost IP. /24 means to only use the first 24 # bits of the 32 bit IP address. the same as netmask 255.255.255.0 # LAN_IP="192.168.0.2" LAN_IP_RANGE="192.168.0.0/16" LAN_IFACE="eth1" # # 1.3 DMZ Configuration. # # # 1.4 Localhost Configuration. # LO_IFACE="lo" LO_IP="127.0.0.1" # # 1.5 IPTables Configuration. # IPTABLES="/usr/sbin/iptables" # # 1.6 Other Configuration. # ########################################################################### # # 2. Module loading. #加载模块 # # # Needed to initially load modules # /sbin/depmod -a # # 2.1 Required modules # /sbin/modprobe ip_tables /sbin/modprobe ip_conntrack /sbin/modprobe iptable_filter /sbin/modprobe iptable_mangle /sbin/modprobe iptable_nat /sbin/modprobe ipt_LOG /sbin/modprobe ipt_limit /sbin/modprobe ipt_state # # 2.2 Non-Required modules # #/sbin/modprobe ipt_owner #/sbin/modprobe ipt_REJECT #/sbin/modprobe ipt_MASQUERADE #/sbin/modprobe ip_conntrack_ftp #/sbin/modprobe ip_conntrack_irc #/sbin/modprobe ip_nat_ftp #/sbin/modprobe ip_nat_irc ########################################################################### # # 3. /proc set up. #设置/proc参数开启转发功能，主要用于nat # # # 3.1 Required proc configuration # echo "1" > /proc/sys/net/ipv4/ip_forward # # 3.2 Non-Required proc configuration # #echo "1" > /proc/sys/net/ipv4/conf/all/rp_filter #echo "1" > /proc/sys/net/ipv4/conf/all/proxy_arp #echo "1" > /proc/sys/net/ipv4/ip_dynaddr ########################################################################### # # 4. rules set up #开始配置具体的规则. # ###### # 4.1 Filter table # # # 4.1.1 Set policies # $IPTABLES -P INPUT DROP $IPTABLES -P OUTPUT DROP $IPTABLES -P FORWARD DROP # # 4.1.2 Create userspecified chains #作者的总体思路是先写好自定义的链，然后再后续的系统预定义链中调用，类似函数的概 #念 # # Create chain for bad tcp packets # $IPTABLES -N bad_tcp_packets # # Create separate chains for ICMP, TCP and UDP to traverse # $IPTABLES -N allowed $IPTABLES -N tcp_packets $IPTABLES -N udp_packets $IPTABLES -N icmp_packets # # 4.1.3 Create content in userspecified chains # # # bad_tcp_packets chain #拒绝或者记录不正常的数据包 # $IPTABLES -A bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK \ -m state --state NEW -j REJECT --reject-with tcp-reset #拒绝带有SYN和ACK标记的状态为NEW的包并返回错误信息 $IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG \ --log-prefix "New not syn:" #不是SYN标记但是状态时NEW的数据包并记录日志 $IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP #拒绝不是SYN标记但是状态时NEW的数据包并记录日志 # # allowed chain #允许特定的数据包 # $IPTABLES -A allowed -p TCP --syn -j ACCEPT #允许带有SYN标记的数据包 $IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT #允许状态为ESTABLISH和RELATED的数据包 $IPTABLES -A allowed -p TCP -j DROP #拒绝其他所有的数据包 # # TCP rules # $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed #允许访问ftp服务 $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed #允许访问ssh服务 $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed #允许访问www服务 $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed #允许访问IRC服务 # # UDP ports # #$IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 53 -j ACCEPT #允许DNS服务 #$IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 123 -j ACCEPT #允许ntp服务 $IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 2074 -j ACCEPT #允许多媒体服务 $IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 4000 -j ACCEPT #允许ICQ服务 # # In Microsoft Networks you will be swamped by broadcasts. These lines # will prevent them from showing up in the logs. # #$IPTABLES -A udp_packets -p UDP -i $INET_IFACE -d $INET_BROADCAST \ #--destination-port 135:139 -j DROP #拒绝微软的netbios的广播服务 # # If we get DHCP requests from the Outside of our network, our logs will # be swamped as well. This rule will block them from getting logged. # #$IPTABLES -A udp_packets -p UDP -i $INET_IFACE -d 255.255.255.255 \ #--destination-port 67:68 -j DROP #拒绝DHCP服务 # # ICMP rules # $IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT #允许8类ICMP服务 $IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT #允许11类ICMP服务 # # 4.1.4 INPUT chain # # # Bad TCP packets we don't want. # $IPTABLES -A INPUT -p tcp -j bad_tcp_packets #检查是否是坏包 # # Rules for special networks not part of the Internet # $IPTABLES -A INPUT -p ALL -i $LAN_IFACE -s $LAN_IP_RANGE -j ACCEPT #来自内部网络的包一律允许通过 $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LO_IP -j ACCEPT #来自本地的包一律通过 $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LAN_IP -j ACCEPT $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $INET_IP -j ACCEPT # # Special rule for DHCP requests from LAN, which are not caught properly # otherwise. # $IPTABLES -A INPUT -p UDP -i $LAN_IFACE --dport 67 --sport 68 -j ACCEPT #允许DHCP服务 # # Rules for incoming packets from the internet. # $IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED \ -j ACCEPT #允许外部过来的响应本地请求或者和本地已有连接有关系的包 $IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets #TCP包由对应链处理 $IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udp_packets #UDP包由对应链处理 $IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets #ICMP包由对应链处理 # # If you have a Microsoft Network on the outside of your firewall, you may # also get flooded by Multicasts. We drop them so we do not get flooded by # logs # #$IPTABLES -A INPUT -i $INET_IFACE -d 224.0.0.0/8 -j DROP #拒绝组播包 # # Log weird packets that don't match the above. # $IPTABLES -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \ --log-level DEBUG --log-prefix "IPT INPUT packet died: " #如果包与上述规则均不匹配则写入日志 # # 4.1.5 FORWARD chain # # # Bad TCP packets we don't want # $IPTABLES -A FORWARD -p tcp -j bad_tcp_packets #先检查是否是坏包 # # Accept the packets we actually want to forward # $IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT #允许由本地发来的包被转发 $IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT #允许ESTABLISHED,RELATED状态的包转发 # # Log weird packets that don't match the above. # $IPTABLES -A FORWARD -m limit --limit 3/minute --limit-burst 3 -j LOG \ --log-level DEBUG --log-prefix "IPT FORWARD packet died: " #如果包与上述规则均不匹配则写入日志 # # 4.1.6 OUTPUT chain # # # Bad TCP packets we don't want. # $IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets #先检查是否是坏包 # # Special OUTPUT rules to decide which IP's to allow. # $IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT #允许所有包通过 $IPTABLES -A OUTPUT -p ALL -s $LAN_IP -j ACCEPT $IPTABLES -A OUTPUT -p ALL -s $INET_IP -j ACCEPT # # Log weird packets that don't match the above. # $IPTABLES -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \ --log-level DEBUG --log-prefix "IPT OUTPUT packet died: " #如果包与上述规则均不匹配则写入日志 ###### # 4.2 nat table # # # 4.2.1 Set policies # # # 4.2.2 Create user specified chains # # # 4.2.3 Create content in user specified chains # # # 4.2.4 PREROUTING chain # # # 4.2.5 POSTROUTING chain # # # Enable simple IP Forwarding and Network Address Translation # $IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j SNAT --to-source $INET_IP #对所有沿外网口出去的包执行SNAT # # 4.2.6 OUTPUT chain # ###### # 4.3 mangle table # # # 4.3.1 Set policies # # # 4.3.2 Create user specified chains # # # 4.3.3 Create content in user specified chains # # # 4.3.4 PREROUTING chain # # # 4.3.5 INPUT chain # # # 4.3.6 FORWARD chain # # # 4.3.7 OUTPUT chain # # # 4.3.8 POSTROUTING chain # ##本脚本来自http: #www.faqs.org/docs/iptables/index.html