A.1. 查看当前规则集的命令

查看当前正在使用的规则集是一个十分常用的操作，使用iptables的什么命令还 记得吗？我们可是在规则是如何练成的这一章里介绍过啊，虽然 到时说得简单了点。再复习一下吧，命令语法如下：

iptables -L

这个命令会尽可能地以易读的形式显示当前正在使用的规则集。比如，它会尽量用文件/etc/services里相应的名字表示端口号，用相应的DNS记录表示IP地址。但后者可能 会导致一些问题，例如，它想尽力把LAN的IP地址（如192.168.1.1）解析 成相应的名字。但192.168.0.0/16这个网段是私有的，也就是说，它只能 用在局域网里，而不能在Internet里使用，所以它不会被Internet上的DNS服务器解析。因此，当解析这个地 址时，命令就好像停在那儿了。为了避免这种情况的发生，我们就要使用选项：

iptables -L -n

如果你想看看每个策略或每条规则、每条链的简单流量统计，可以在上面的命令后再加一个verbose标 志，如下：

iptables -L -n -v

不要忘了，iptables -L命令还可以查看nat表和mangle表的内容哦（更不要忘 了，默认的表是filter），只需要使用-t选项,比如我们只想看nat表的规则，就用下面的命令：

iptables -L -t nat

在/proc里，可能还有一些文件你会感兴趣。比如，你可以在连接跟踪记录表 里看到当前有哪些连接。这个表包含了当前的所有连接，你还可以通过它了解到每个连接处于什么状态。要 注意，这个表是不能编辑的，即使可以，也不应该更改它。可以用下面的命令查看这个表：

cat /proc/net/ip_conntrack | less

此命令会显示当前所有被跟踪的连接，但要读懂那些记录可是有些难度哦。

A.2. 修正和清空iptables的命令

即使你把iptables弄的一塌糊涂，我们也有非常有效的命令来处理，而不必重新启动计算机。我接到过很 多关于这个问题的询问，所以我想最好在这儿回答一下。如果你增加的规则有问题，要想删掉它，只要把命 令中的-A改为-D即可。这样，iptables就会找到那个错误的 规则并删掉它，但如果在你的规则里有好几条同样的规则，它只能删掉找到的第一条。如果你不想这样的事 情发生，那就试试用序号来删除。如，你想删除INPUT链的第10条规则，可以使用 iptables -D INPUT 10。

还有一种情况，就是要清空整个链，这就要使用选项-F。比如，我们要清空整个 INPUT链，使用的命令就是iptables -F INPUT。但是要注意，选项-F并不改变链的缺省策 略。所以，如果被我们清空的那条INPUT链的策略是DROP，它还是会阻塞所有的包。那怎么才能重置策略呢？ 还记得策略DROP是如何设置的吧，还是用那个方法啊。比如，我们把INPUT链的策略改为ACCEPT，就用iptables -P INPUT ACCEPT。

我已经写了一个用来清空并重置iptables的脚本，叫做rc.flush- iptables.txt（附录里有它的代码），在你写自己的防火 墙脚本时，很可能会用到。但如果你在mangle表里乱试乱改而导致问题的话，这个脚本就帮不上忙了。因为 在脚本rc.firewall.txt里，我没有用到mangle表，所以在 rc.flush-iptables.txt里也就没有添加相应的恢复功能。

B.1. 模块装载问题

装载模块时，你可能会遇到几个问题，比如，有错误提示说明没有你指定名字的那种模块：

insmod: iptable_filter: no module by 
that name found

这个提示是无关紧要的，因为那些模块很有可能已经被静态地编译进内核了。当你遇到这个信息时，这是 你应该首先想到的。至于是否真的如我们所想，最简单的测试方就是敲一个用到那个模块功能的命令试试。 对于上面的情况，可能是filter表没有装入，从而就没有相应的功能，当然不能使用filter表了。为了检查 filter表是否装入，可以用下面的命令来试试：

iptables -t filter -L
   

这个命令会输出filter表里所有的链，或者是运行失败，给出错误提示信息。如果一切正常，输出结果类 似下面的情况，当然，这还要看你是否已经在filter表里加入了规则（译者注：在这个例子里，表是空 的）。

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
    

如果你确实没有装载filter表，得到的就是如下信息：

iptables 
v1.2.5: can‘t initialize iptables table `filter‘: Table      does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.
    

这个问题就有些严重了，从此提示中我们能得到两个信息：第一，我们确实没有把相应的功能编译进内核 里；第二，在模块一般应在的目录中没有找到这个模块。这意味着问题是，你或者忘记了装载想用的模块， 或者没有用depmod -a命令更新模块数据库，或者没有把相应的功能编译进内核（不 论是静态的还是作为模块）。当然还可能是其他原因，但这些是主要的，不管怎样，大部分原因是很容易解 决的。比如，第一个问题可以简单地通过在内核源码目录里运行make modules_install 命令来解决，这当然是有前提的，就是源码已经编译（compile）而且模块已经构建（build）。第二个 问题的解决办法也很简单，只要运行一下depmod -a命令，之后再看看能否正常工作即可。第三个问题有点超出我们的范围了，而 且这个问题或多或少会让你感到发晕。更多的信息可以在Linux文档计划里找 到。

在运行iptables时，你还可能得到另外一个错误信息：

iptables: No chain/target/match by that name
   

这说明你要用的链或target、或match不存在，原因有很多，但最普遍的是你拼错了名字。当你想使用一 个不可用的模块时也会产生这种错误。模块之所以不可用，可能是因为你没有装载正确的模块，或者内核里 不包含那个模块，或者是iptables自动装载模块时失败了。通常，你不止应该考虑上面提到的所有解决办 法，还要考虑规则中target的拼写错误，或者其他的原因。

B.2. 未设置SYN的NEW状态包

iptables有个“特点”没有被很好地给以说明，所以很多人（当然，也包括我）都忽视了它。这个“特 点”就是：如果你使用状态NEW，那么未设置SYN的包也会通过防火墙。之所以有这个特点，是因为在某些情况下， 我们想把那样的包看作某个（比如是和另一个防火墙有关的）已处于ESTABLISHED状 态的连接的一部分。这个特点使拥有两个或更多的防火墙协同工作成为可能，而且可使数据在服务器间无丢 失的传输，如辅助防火墙可以接受子网的防火墙的操作。但它也会导致这样的事情：状态 NEW会允许几乎所有的TCP连接进入，而不管是否有3次握手。为了处理这个问题，我们需要在防火墙的 INPUT链、OUTPUT链和FORWARD链加入如下规则（译者注：此规则作者称为“NEW not SYN rules”，下一小节 还会提到）：

$IPTABLES -A 
INPUT -p tcp ! --syn -m state --state NEW -j LOG      --log-prefix "New not syn:"
$IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j DROP
    

 

警告，在Netfilter/iptables项目中，这个特点所 拥有的行为缺少文档说明，更明确的说，在你的防火墙上，它是一个很不安全的因素。

注意，这个规则用于microsoft的TCP/IP（微软实现的TCP/IP就是不行，至少现在不行）产生的包时还是 有些问题。如果包是由microsoft的产品生成的，且被标为状态NEW，那么就会被此规 则记录然后丢弃。看起来规则工作很正常啊，是吧。但问题就出在这儿了，因为连接无法中断了。这个问题 出现在关闭连接时，在最后一个包即FIN/ACK包发出后，Netfilter的状态机制就会关 闭连接、删除连接跟踪表里的相应记录。但就在这时，Microsoft那不完善的程序会发送另外一个包，这个包 就是那种未设置SYN且被认为是NEW状态的包，因此它就会被上面的规则匹配。换句话说，就是对这个规则不 需要过于关注，如果你很在意它，就在规则里加入选项--log-headers吧。这样，你 就可以把包头记录下来，从而可以更好地了解相应的包。

对于这个规则，还有一些已知的问题。比如，某个连接（比如是从LAN发出的）已经连接到防火墙，而且 有个脚本要在启动PPP时激活。当你启动PPP连接时，刚才提到的那个连接可能就会被干掉（be killed）。当 然，这只会在特定的情况下才能发生，就是你把conntrack和nat作为模块运行，并且每次运行那个脚本时这 两个模块都要被装入和卸载。如果你在防火墙之外的机子上运行telnet，而且又通过这个telnet连接运行脚 本rc.firewall.txt，也会导致上面的问题。为了能简单地表达这个问题，你先准 备一个telnet连接，或其他的流连接，再运行连接跟踪模块，然后装入上面的规则，最后，试着用telnet client或daemon发送一些数据。效果应该出来了，连接 跟踪代码会认为这个连接是非法的，因为在此之前，它没有看到任何方向有包发出，更为严重的是现在连接 上有了未设置SYN的包，因为刚才由telnet client或daemon发出的包肯定不是这个连接的第一个包。因此， 上面的规则就起作用了，也就是说，这个包会被记录下来，然后被无情地扔掉，从而连接就会中断。

B.3. NEW状态的SYN/ACK包

某些，TCP欺骗攻击所用的技术叫做序列号预测（Sequence Number Prediction）。在这类攻击中，攻击 者利用另一台机子的IP访问攻击对象（译者注：这就是为什么叫欺骗的原因了，攻击者是想假冒另一台被攻 击对象信任的机子，以达到欺骗攻击对象的目的），然后再试着预测攻击对象使用什么序列号。

我们来看看典型的使用序列号预测技术的欺骗是如何实现的，参与者：攻击者[A]（attacker）试图假装 另一台机子[O]（other host）向受害者[V]（victim）发送数据。

1. [A]以[O]的IP为源地址向[V]发SYN。

2. [V]向[O]回应SYN/ACK。

3. 现在，若[O]以RST回应这个未知的SYN/ACK，攻击就失败了，但如果[O]已经没有这个能力了呢？比如它 早已被另外的攻击（如SYN flood）降服，或者被关闭，或者它的RST包被防火墙拒绝。

4. 如果[O]没能破坏这条连接，而且[A]猜对了序列号，那它就能以[O]的身份和[V]交谈了。

只要我们没能在第三步以RST回应那个未知的SYN/ACK包，[V]就会被攻击，而且我们还会被连累（译者 注：因为我们本身也被攻击了，而且还可能会成为攻击者的替罪羊被起诉，呜呜，好惨）。所以，为安全起 见，我们应该以正确的方式向[V]发送一个RST包。如果我们使用类似“NEW not SYN rules”（译者注：在上 一小节中）的规则，SYN/ACK包就可以被丢弃了。因此，我们在bad_tcp_packets链中加入了如下规则：

iptables -A 
bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK -m state --state NEW -j REJECT --reject-with tcp-reset
   

这样，你想成为上面那个[O]的机会就很少了（译者注：作者好幽默啊，我们可不想成为被别人利用的对 象），而且这条规则在绝大部分情况下是安全的，不会有什么副作用，但多个防火墙要协同工作的情况要除 外。那种情况下，防火墙之间会经常传递、接受包或流，有了这条规则，有些连接可能会被阻塞，即使是合 法的连接。这条规则的存在还产生了另外一问题，就是有几个portscan（端口扫描器）会看到我们的防火 墙，但好在仅此而已。

B.4. 使用私有IP地址的ISP

我的一位朋友告诉我说有些事我完全忘记了，从那时起，我就把这一节加上了。你刚上网时连接的网络是 ISP提供的，但某些愚蠢的ISP在那个网络里使用的是私有地址，而那是IANA专门分 配给局域网使用的。Swedish Internet Service Provider和电话垄断企业Telia就是这样做的，例如在DNS服 务器上，他们使用的IP地址段就是10.x.x.x。我们最容易遇到的问题是，在这个脚本里，为了防止被欺骗， 不允许从10.x.x.x发出的连接来访问我们。不幸的是，对于上面的例子，为了DNS能正常地被访问，我们不得 不把规则的放宽松一些。也就是说，我们或者在刚才提到的那条防止欺骗的规则上面增加一条规则（如 下），或者是把那条规则注释掉：

/usr/local/sbin/iptables -t nat -I PREROUTING -i 
eth1 -s      10.0.0.1/32 -j ACCEPT
   

我愿意对这些ISP再多费些唇舌。这些IP地址不是为了让你象这样愚蠢的使用而分配给你的，至少我知道 不是这样的。对于一个大集团的站点或者是我们自己的家庭网络来说，这样用是很合适的，但你不能只因为 你们的一些原因就强迫我们把自己公示于天下。

B.5. 放行DHCP数据

一旦你了解DHCP是如何工作的，就会知道这其实是一个很简单的任务。但你必须小心处理到底让谁进入、 不让谁进入。首先，我们要明白DHCP是工作在UDP协议之上的，所以，UDP协议是我们期望的第一个条件。其 次，我们应该检查是从那个接口接收和发送请求的。例如，如果我们设置了DHCP使用接口eth0，那就要阻塞 eth1上的DHCP请求。为了让规则再详细些，我们只需打开（allow）DHCP实际使用的UDP端口，一般都是67和 68。这两个端口是标准定义，我们就用它们来匹配被允许的包。现在，规则应该是这个样子的：

$IPTABLES  -I INPUT -i $LAN_IFACE -p udp --dport 67:68 --sport      67:68 -j ACCEPT
   

注意，现在我们能够接受所有来自和发往UDP端口67、68的数据，好像不太安全，但这并不是多大的问 题，因为这条规则只允许从67或68端口连接的主机才能访问。当然，此规则还可以更严谨一些，但也应该足 够接受所有的DHCP请求和更新，而不至于需要在防火墙上开一个大洞。如果你很在意现在的规则是否很宽 松，你当然可以写一个限制条件更紧的。

B.6. 关于mIRC DCC的问题

mIRC使用一个特殊的设定，它可以使mIRC连接穿过防火墙，也可以使DCC连接能在防火墙不了解它的情况 下正常工作。如果此选项和iptables还有ip_conntrack_irc模块与ip_nat_irc模块一起使用，那mIRC就不能 工作了。问题在于mIRC会自动对包进行NAT操作，这样当包到达防火墙后，防火墙就完全不知道该对包做什么 了，也不知道该怎么做。如果是防火墙来处理，它只是简单地用自己的IP去询问IRC服务器，然后用那个地址 发送DCC请求。mIRC不希望防火墙自作聪明地以这种方式代替自己来处理这个包。

打开“I am behind a firewall”（我在防火墙后）这个配置选项并且使用ip_conntrack_irc和 ip_nat_irc模块，会导致Netfilter建立包含“Forged DCC send packet”的记录。

最简单的解决办法是不要选中mIRC的那个选项而让iptables来做这些工作。意思就是要明确地告诉mIRC， 它不是在防火墙后面的。

I.1. rc.firewall脚本代码

#!/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.
#

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.
#

#
# 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.
#

#
# 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.
#

######
# 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
#

#
# 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
#

$IPTABLES -A bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK -m state --state NEW -j REJECT --reject-with tcp-reset 
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "New not syn:"
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP

#
# allowed chain
#

$IPTABLES -A allowed -p TCP --syn -j ACCEPT
$IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A allowed -p TCP -j DROP

#
# TCP rules
#

$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed

#
# UDP ports
#

#$IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 53 -j ACCEPT
#$IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 123 -j ACCEPT
$IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 2074 -j ACCEPT
$IPTABLES -A udp_packets -p UDP -s 0/0 --destination-port 4000 -j ACCEPT

#
# 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

#
# 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

#
# ICMP rules
#

$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

#
# 4.1.4 INPUT chain
#

#
# Bad TCP packets we don‘t want.
#

$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

#
# Rules for special networks not part of the Internet
#

$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -s $LAN_IP_RANGE -j ACCEPT
$IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LO_IP -j ACCEPT
$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

#
# Rules for incoming packets from the internet.
#

$IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets
$IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udp_packets
$IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets

#
# 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

#
# 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: "

#
# 4.1.5 FORWARD chain
#

#
# Bad TCP packets we don‘t want
#

$IPTABLES -A FORWARD -p tcp -j bad_tcp_packets

#
# Accept the packets we actually want to forward
#

$IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

#
# 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: "

#
# 4.1.6 OUTPUT chain
#

#
# Bad TCP packets we don‘t want.
#

$IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets

#
# Special OUTPUT rules to decide which IP‘s to allow.
#

$IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$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: "

######
# 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

#
# 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
#

    

I.2. rc.DMZ.firewall脚本代码

#!/bin/sh
#
# rc.DMZ.firewall - DMZ 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.
#

INET_IP="194.236.50.152"
HTTP_IP="194.236.50.153"
DNS_IP="194.236.50.154"
INET_IFACE="eth0"

#
# 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="192.168.0.1"
LAN_IFACE="eth1"

#
# 1.3 DMZ Configuration.
#

DMZ_HTTP_IP="192.168.1.2"
DMZ_DNS_IP="192.168.1.3"
DMZ_IP="192.168.1.1"
DMZ_IFACE="eth2"

#
# 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.
#

#
# 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.
#

#
# 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.
#

######
# 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
#

#
# 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 icmp_packets

#
# 4.1.3 Create content in userspecified chains
#

#
# bad_tcp_packets chain
#

$IPTABLES -A bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK -m state --state NEW -j REJECT --reject-with tcp-reset
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "New not syn:"
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP

#
# allowed chain
#

$IPTABLES -A allowed -p TCP --syn -j ACCEPT
$IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A allowed -p TCP -j DROP

#
# ICMP rules
#

# Changed rules totally
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

#
# 4.1.4 INPUT chain
#

#
# Bad TCP packets we don‘t want
#

$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

#
# Packets from the Internet to this box
#

$IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets

#
# Packets from LAN, DMZ or LOCALHOST
#

#
# From DMZ Interface to DMZ firewall IP
#

$IPTABLES -A INPUT -p ALL -i $DMZ_IFACE -d $DMZ_IP -j ACCEPT

#
# From LAN Interface to LAN firewall IP
#

$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_IP -j ACCEPT

#
# From Localhost interface to Localhost IP‘s
#

$IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LO_IP -j ACCEPT
$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

#
# All established and related packets incoming from the internet to the
# firewall
#

$IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED -j ACCEPT

#
# In Microsoft Networks you will be swamped by broadcasts. These lines
# will prevent them from showing up in the logs.
#

#$IPTABLES -A INPUT -p UDP -i $INET_IFACE -d $INET_BROADCAST #--destination-port 135:139 -j DROP

#
# 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 INPUT -p UDP -i $INET_IFACE -d 255.255.255.255 #--destination-port 67:68 -j DROP

#
# 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

#
# 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: "

#
# 4.1.5 FORWARD chain
#

#
# Bad TCP packets we don‘t want
#

$IPTABLES -A FORWARD -p tcp -j bad_tcp_packets


#
# DMZ section
#
# General rules
#

$IPTABLES -A FORWARD -i $DMZ_IFACE -o $INET_IFACE -j ACCEPT
$IPTABLES -A FORWARD -i $INET_IFACE -o $DMZ_IFACE -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -i $LAN_IFACE -o $DMZ_IFACE -j ACCEPT
$IPTABLES -A FORWARD -i $DMZ_IFACE -o $LAN_IFACE -m state --state ESTABLISHED,RELATED -j ACCEPT

#
# HTTP server
#

$IPTABLES -A FORWARD -p TCP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_HTTP_IP --dport 80 -j allowed
$IPTABLES -A FORWARD -p ICMP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_HTTP_IP -j icmp_packets

#
# DNS server
#

$IPTABLES -A FORWARD -p TCP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_DNS_IP --dport 53 -j allowed
$IPTABLES -A FORWARD -p UDP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_DNS_IP --dport 53 -j ACCEPT
$IPTABLES -A FORWARD -p ICMP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_DNS_IP -j icmp_packets

#
# LAN section
#

$IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

#
# 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: "

#
# 4.1.6 OUTPUT chain
#

#
# Bad TCP packets we don‘t want.
#

$IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets

#
# Special OUTPUT rules to decide which IP‘s to allow.
#

$IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$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: "

######
# 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
#

$IPTABLES -t nat -A PREROUTING -p TCP -i $INET_IFACE -d $HTTP_IP --dport 80 -j DNAT --to-destination $DMZ_HTTP_IP
$IPTABLES -t nat -A PREROUTING -p TCP -i $INET_IFACE -d $DNS_IP --dport 53 -j DNAT --to-destination $DMZ_DNS_IP
$IPTABLES -t nat -A PREROUTING -p UDP -i $INET_IFACE -d $DNS_IP --dport 53 -j DNAT --to-destination $DMZ_DNS_IP

#
# 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

#
# 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
#

    

I.3. rc.UTIN.firewall脚本代码

#!/bin/sh
#
# rc.firewall - UTIN 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.
#

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.
#

#
# 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.
#

#
# 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.
#

######
# 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
#

#
# 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
#

$IPTABLES -A bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK -m state --state NEW -j REJECT --reject-with tcp-reset
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "New not syn:"
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP

#
# allowed chain
#

$IPTABLES -A allowed -p TCP --syn -j ACCEPT
$IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A allowed -p TCP -j DROP

#
# TCP rules
#

$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed

#
# UDP ports
#

#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT
#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT
$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT
$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT

#
# 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

#
# 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

#
# ICMP rules
#

$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

#
# 4.1.4 INPUT chain
#

#
# Bad TCP packets we don‘t want.
#

$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

#
# Rules for special networks not part of the Internet
#

$IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LO_IP -j ACCEPT
$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

#
# Rules for incoming packets from anywhere.
#

$IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -p TCP -j tcp_packets
$IPTABLES -A INPUT -p UDP -j udp_packets
$IPTABLES -A INPUT -p ICMP -j icmp_packets

#
# 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

#
# 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: "

#
# 4.1.5 FORWARD chain
#

#
# Bad TCP packets we don‘t want
#

$IPTABLES -A FORWARD -p tcp -j bad_tcp_packets

#
# Accept the packets we actually want to forward
#

$IPTABLES -A FORWARD -p tcp --dport 21 -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -p tcp --dport 80 -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -p tcp --dport 110 -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

#
# 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: "

#
# 4.1.6 OUTPUT chain
#

#
# Bad TCP packets we don‘t want.
#

$IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets

#
# Special OUTPUT rules to decide which IP‘s to allow.
#

$IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$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: "

######
# 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

#
# 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
#

    

I.4. rc.DHCP.firewall脚本代码

#!/bin/sh
#
# rc.firewall - DHCP 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.
#

INET_IFACE="eth0"

#
# 1.1.1 DHCP
#

#
# Information pertaining to DHCP over the Internet, if needed.
#
# Set DHCP variable to no if you don‘t get IP from DHCP. If you get DHCP
# over the Internet set this variable to yes, and set up the proper IP
# address for the DHCP server in the DHCP_SERVER variable.
#

DHCP="no"
DHCP_SERVER="195.22.90.65"

#
# 1.1.2 PPPoE
#

# Configuration options pertaining to PPPoE.
#
# If you have problem with your PPPoE connection, such as large mails not
# getting through while small mail get through properly etc, you may set
# this option to "yes" which may fix the problem. This option will set a
# rule in the PREROUTING chain of the mangle table which will clamp
# (resize) all routed packets to PMTU (Path Maximum Transmit Unit).
#
# Note that it is better to set this up in the PPPoE package itself, since
# the PPPoE configuration option will give less overhead.
#

PPPOE_PMTU="no"

#
# 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.
#

#
# Needed to initially load modules
#

/sbin/depmod -a

#
# 2.1 Required modules
#

/sbin/modprobe ip_conntrack
/sbin/modprobe ip_tables
/sbin/modprobe iptable_filter
/sbin/modprobe iptable_mangle
/sbin/modprobe iptable_nat
/sbin/modprobe ipt_LOG
/sbin/modprobe ipt_limit
/sbin/modprobe ipt_MASQUERADE

#
# 2.2 Non-Required modules
#

#/sbin/modprobe ipt_owner
#/sbin/modprobe ipt_REJECT
#/sbin/modprobe ip_conntrack_ftp
#/sbin/modprobe ip_conntrack_irc
#/sbin/modprobe ip_nat_ftp
#/sbin/modprobe ip_nat_irc

###########################################################################
#
# 3. /proc set up.
#

#
# 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.
#

######
# 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
#

#
# 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
#

$IPTABLES -A bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK -m state --state NEW -j REJECT --reject-with tcp-reset
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "New not syn:"
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP

#
# allowed chain
#

$IPTABLES -A allowed -p TCP --syn -j ACCEPT
$IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A allowed -p TCP -j DROP

#
# TCP rules
#

$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed

#
# UDP ports
#

$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT
if [ $DHCP == "yes" ] ; then
 $IPTABLES -A udp_packets -p UDP -s $DHCP_SERVER --sport 67  --dport 68 -j ACCEPT
fi

#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT
#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT
$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT
$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT

#
# 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 #--destination-port 135:139 -j DROP

#
# 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

#
# ICMP rules
#

$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

#
# 4.1.4 INPUT chain
#

#
# Bad TCP packets we don‘t want.
#

$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

#
# Rules for special networks not part of the Internet
#

$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -s $LAN_IP_RANGE -j ACCEPT
$IPTABLES -A INPUT -p ALL -i $LO_IFACE -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

#
# Rules for incoming packets from the internet.
#

$IPTABLES -A INPUT -p ALL -i $INET_IFACE -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets
$IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udp_packets
$IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets

#
# 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

#
# 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: "

#
# 4.1.5 FORWARD chain
#

#
# Bad TCP packets we don‘t want
#

$IPTABLES -A FORWARD -p tcp -j bad_tcp_packets

#
# Accept the packets we actually want to forward
#

$IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

#
# 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: "

#
# 4.1.6 OUTPUT chain
#

#
# Bad TCP packets we don‘t want.
#

$IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets

#
# Special OUTPUT rules to decide which IP‘s to allow.
#

$IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -s $LAN_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -o $INET_IFACE -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: "

######
# 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
#

if [ $PPPOE_PMTU == "yes" ] ; then
 $IPTABLES -t nat -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN  -j TCPMSS --clamp-mss-to-pmtu
fi
$IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j MASQUERADE

#
# 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
#

    

I.5. rc.flush-iptables脚本代码

#!/bin/sh
# 
# rc.flush-iptables - Resets iptables to default values. 
# 
# 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

#
# Configurations
#
IPTABLES="/usr/sbin/iptables"

#
# reset the default policies in the filter table.
#
$IPTABLES -P INPUT ACCEPT
$IPTABLES -P FORWARD ACCEPT
$IPTABLES -P OUTPUT ACCEPT

#
# reset the default policies in the nat table.
#
$IPTABLES -t nat -P PREROUTING ACCEPT
$IPTABLES -t nat -P POSTROUTING ACCEPT
$IPTABLES -t nat -P OUTPUT ACCEPT

#
# reset the default policies in the mangle table.
#
$IPTABLES -t mangle -P PREROUTING ACCEPT
$IPTABLES -t mangle -P OUTPUT ACCEPT

#
# flush all the rules in the filter and nat tables.
#
$IPTABLES -F
$IPTABLES -t nat -F
$IPTABLES -t mangle -F
#
# erase all chains that‘s not default in filter and nat table.
#
$IPTABLES -X
$IPTABLES -t nat -X
$IPTABLES -t mangle -X



    

I.6. rc.test-iptables脚本代码

#!/bin/bash
#
# rc.test-iptables - test script for iptables chains and tables.
#
# 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
#

#
# Filter table, all chains
#
iptables -t filter -A INPUT -p icmp --icmp-type echo-request -j LOG --log-prefix="filter INPUT:"
iptables -t filter -A INPUT -p icmp --icmp-type echo-reply -j LOG --log-prefix="filter INPUT:"
iptables -t filter -A OUTPUT -p icmp --icmp-type echo-request -j LOG --log-prefix="filter OUTPUT:"
iptables -t filter -A OUTPUT -p icmp --icmp-type echo-reply -j LOG --log-prefix="filter OUTPUT:"
iptables -t filter -A FORWARD -p icmp --icmp-type echo-request -j LOG --log-prefix="filter FORWARD:"
iptables -t filter -A FORWARD -p icmp --icmp-type echo-reply -j LOG --log-prefix="filter FORWARD:"

#
# NAT table, all chains except OUTPUT which don‘t work.
#
iptables -t nat -A PREROUTING -p icmp --icmp-type echo-request -j LOG --log-prefix="nat PREROUTING:"
iptables -t nat -A PREROUTING -p icmp --icmp-type echo-reply -j LOG --log-prefix="nat PREROUTING:"
iptables -t nat -A POSTROUTING -p icmp --icmp-type echo-request -j LOG --log-prefix="nat POSTROUTING:"
iptables -t nat -A POSTROUTING -p icmp --icmp-type echo-reply -j LOG --log-prefix="nat POSTROUTING:"
iptables -t nat -A OUTPUT -p icmp --icmp-type echo-request -j LOG --log-prefix="nat OUTPUT:"
iptables -t nat -A OUTPUT -p icmp --icmp-type echo-reply -j LOG --log-prefix="nat OUTPUT:"

#
# Mangle table, all chains
#
iptables -t mangle -A PREROUTING -p icmp --icmp-type echo-request -j LOG --log-prefix="mangle PREROUTING:"
iptables -t mangle -A PREROUTING -p icmp --icmp-type echo-reply -j LOG --log-prefix="mangle PREROUTING:"
iptables -t mangle -I FORWARD 1 -p icmp --icmp-type echo-request -j LOG --log-prefix="mangle FORWARD:"
iptables -t mangle -I FORWARD 1 -p icmp --icmp-type echo-reply -j LOG --log-prefix="mangle FORWARD:"
iptables -t mangle -I INPUT 1 -p icmp --icmp-type echo-request -j LOG --log-prefix="mangle INPUT:"
iptables -t mangle -I INPUT 1 -p icmp --icmp-type echo-reply -j LOG --log-prefix="mangle INPUT:"
iptables -t mangle -A OUTPUT -p icmp --icmp-type echo-request -j LOG --log-prefix="mangle OUTPUT:"
iptables -t mangle -A OUTPUT -p icmp --icmp-type echo-reply -j LOG --log-prefix="mangle OUTPUT:"
iptables -t mangle -I POSTROUTING 1 -p icmp --icmp-type echo-request -j LOG --log-prefix="mangle POSTROUTING:"
iptables -t mangle -I POSTROUTING 1 -p icmp --icmp-type echo-reply -j LOG --log-prefix="mangle POSTROUTING:"