1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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4 | <!ENTITY % general-entities SYSTEM "../../general.ent">
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5 | %general-entities;
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6 |
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7 | <!ENTITY iptables-download-http "https://www.netfilter.org/projects/iptables/files/iptables-&iptables-version;.tar.xz">
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8 | <!--<!ENTITY iptables-download-ftp "ftp://ftp.netfilter.org/pub/iptables/iptables-&iptables-version;.tar.xz">-->
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9 | <!ENTITY iptables-download-ftp " ">
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10 | <!ENTITY iptables-md5sum "ffa00f68d63e723c21b8a091c5c0271b">
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11 | <!ENTITY iptables-size "633 KB">
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12 | <!ENTITY iptables-buildsize "16 MB">
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13 | <!ENTITY iptables-time "0.1 SBU">
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14 | ]>
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15 |
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16 | <sect1 id="iptables" xreflabel="iptables-&iptables-version;">
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17 | <?dbhtml filename="iptables.html"?>
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18 |
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19 |
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20 | <title>iptables-&iptables-version;</title>
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21 |
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22 | <indexterm zone="iptables">
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23 | <primary sortas="a-iptables">iptables</primary>
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24 | </indexterm>
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25 |
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26 | <sect2 role="package">
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27 | <title>Introduction to iptables</title>
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28 |
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29 | <para>
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30 | <application>iptables</application> is a userspace command line program
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31 | used to configure the Linux 2.4 and later kernel packet filtering ruleset.
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32 | </para>
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33 |
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34 | &lfs120_checked;
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35 |
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36 | <bridgehead renderas="sect3">Package Information</bridgehead>
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37 | <itemizedlist spacing="compact">
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38 | <listitem>
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39 | <para>
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40 | Download (HTTP): <ulink url="&iptables-download-http;"/>
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41 | </para>
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42 | </listitem>
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43 | <listitem>
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44 | <para>
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45 | Download (FTP): <ulink url="&iptables-download-ftp;"/>
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46 | </para>
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47 | </listitem>
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48 | <listitem>
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49 | <para>
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50 | Download MD5 sum: &iptables-md5sum;
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51 | </para>
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52 | </listitem>
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53 | <listitem>
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54 | <para>
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55 | Download size: &iptables-size;
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56 | </para>
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57 | </listitem>
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58 | <listitem>
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59 | <para>
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60 | Estimated disk space required: &iptables-buildsize;
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61 | </para>
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62 | </listitem>
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63 | <listitem>
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64 | <para>
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65 | Estimated build time: &iptables-time;
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66 | </para>
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67 | </listitem>
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68 | </itemizedlist>
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69 |
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70 | <bridgehead renderas="sect3">iptables Dependencies</bridgehead>
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71 |
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72 | <bridgehead renderas="sect4">Optional</bridgehead>
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73 | <para role="optional">
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74 | <!-- <xref linkend="nftables"/>, -->
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75 | <xref linkend="libpcap"/> (required for BPF compiler or nfsynproxy support),
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76 | <ulink url="https://github.com/tadamdam/bpf-utils">bpf-utils</ulink>
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77 | (required for Berkeley Packet Filter support),
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78 | <ulink url="https://netfilter.org/projects/libnfnetlink/">libnfnetlink</ulink>
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79 | (required for connlabel support),
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80 | <ulink url="https://netfilter.org/projects/libnetfilter_conntrack/">libnetfilter_conntrack</ulink>
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81 | (required for connlabel support), and
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82 | <ulink url="https://netfilter.org/projects/nftables/">nftables</ulink>
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83 | </para>
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84 |
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85 | </sect2>
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86 |
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87 | <sect2 role="kernel" id="iptables-kernel">
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88 | <title>Kernel Configuration</title>
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89 |
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90 | <para>
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91 | A firewall in Linux is accomplished through the netfilter interface. To
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92 | use <application>iptables</application> to configure netfilter, the
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93 | following kernel configuration parameters are required:
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94 | </para>
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95 |
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96 | <xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
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97 | href="iptables-kernel.xml"/>
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98 |
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99 | <para>
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100 | Include any connection tracking protocols that will be used, as well as
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101 | any protocols that you wish to use for match support under the
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102 | "Core Netfilter Configuration" section. The above options are enough
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103 | for running <xref linkend="fw-persFw-ipt"/> below.
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104 | </para>
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105 |
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106 | <indexterm zone="iptables iptables-kernel">
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107 | <primary sortas="d-iptables">iptables</primary>
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108 | </indexterm>
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109 |
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110 | </sect2>
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111 |
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112 | <sect2 role="installation">
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113 | <title>Installation of iptables</title>
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114 |
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115 | <note>
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116 | <para>
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117 | The installation below does not include building some specialized
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118 | extension libraries which require the raw headers in the
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119 | <application>Linux</application> source code. If you wish to build the
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120 | additional extensions (if you aren't sure, then you probably don't), you
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121 | can look at the <filename>INSTALL</filename> file to see an example of
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122 | how to change the <parameter>KERNEL_DIR=</parameter> parameter to point
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123 | at the <application>Linux</application> source code. Note that if you
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124 | upgrade the kernel version, you may also need to recompile
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125 | <application>iptables</application> and that the BLFS team has not
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126 | tested using the raw kernel headers.
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127 | </para>
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128 | </note>
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129 |
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130 | <para>
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131 | Install <application>iptables</application> by running the following
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132 | commands:
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133 | </para>
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134 |
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135 | <screen><userinput>./configure --prefix=/usr \
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136 | --disable-nftables \
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137 | --enable-libipq &&
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138 | make</userinput></screen>
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139 |
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140 | <para>
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141 | <!-- there is a iptables-test.py script which seems to run a
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142 | lot of tests. Unfortunately, success rate is 50% only. Needs
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143 | to be clarified how to use and which prerequisites are required
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144 | to run to 100%. Contacted Shekhar Sharma for that (Dec'19),
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145 | waiting for answer (thomas). -->
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146 | This package does not come with a test suite.
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147 | </para>
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148 |
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149 | <para>
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150 | Now, as the <systemitem class="username">root</systemitem> user:
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151 | </para>
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152 |
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153 | <screen role="root"><userinput>make install</userinput></screen>
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154 |
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155 | </sect2>
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156 |
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157 | <sect2 role="commands">
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158 | <title>Command Explanations</title>
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159 |
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160 | <para>
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161 | <parameter>--disable-nftables</parameter>: This switch disables building
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162 | nftables compatibility. <!--Omit this switch if you have installed
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163 | <xref linkend="nftables"/>.-->
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164 | </para>
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165 |
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166 | <para>
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167 | <parameter>--enable-libipq</parameter>: This switch enables building
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168 | of <filename class="libraryfile">libipq.so</filename> which
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169 | can be used by some packages outside of BLFS.
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170 | </para>
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171 |
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172 | <para>
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173 | <option>--enable-nfsynproxy</option>: This switch enables installation
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174 | of <application>nfsynproxy</application> SYNPROXY configuration tool.
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175 | </para>
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176 |
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177 | </sect2>
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178 |
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179 | <sect2 role="configuration">
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180 | <title>Configuring iptables</title>
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181 | <!--
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182 | <note>
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183 | <para>
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184 | If you intend to use <xref linkend="firewalld"/> to configure your
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185 | firewall rules, you should not use the example configurations provided
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186 | here, nor should you enable the
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187 | <phrase revision="sysv">bootscript.</phrase>
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188 | <phrase revision="systemd">systemd unit.</phrase>
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189 | </para>
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190 | </note>
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191 | -->
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192 | <note>
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193 | <para>
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194 | In the following example configurations, <emphasis
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195 | role="strong">LAN1</emphasis> is used for the internal LAN interface,
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196 | and <emphasis role="strong">WAN1</emphasis> is used for the external
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197 | interface connected to the Internet. You will need to replace these
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198 | values with appropriate interface names for your system.
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199 | </para>
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200 | </note>
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201 |
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202 | <sect3 id="fw-persFw-ipt"
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203 | xreflabel="Creating a Personal Firewall With iptables">
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204 | <title>Personal Firewall</title>
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205 |
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206 | <para>
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207 | A Personal Firewall is designed to let you access all the
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208 | services offered on the Internet while keeping your computer secure and
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209 | your data private.
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210 | </para>
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211 |
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212 | <para>
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213 | Below is a slightly modified version of Rusty Russell's
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214 | recommendation from the <ulink
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215 | url="https://www.netfilter.org/documentation/HOWTO/packet-filtering-HOWTO.html">
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216 | Linux 2.4 Packet Filtering HOWTO</ulink>. It is still applicable
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217 | to the Linux 5.x kernels.
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218 | </para>
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219 |
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220 | <screen role="root" revision="sysv"><?dbfo keep-together="auto"?><userinput>cat > /etc/rc.d/rc.iptables << "EOF"
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221 | <literal>#!/bin/sh
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222 |
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223 | # Begin rc.iptables
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224 |
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225 | # Insert connection-tracking modules
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226 | # (not needed if built into the kernel)
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227 | modprobe nf_conntrack
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228 | modprobe xt_LOG
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229 |
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230 | # Enable broadcast echo Protection
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231 | echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
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232 |
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233 | # Disable Source Routed Packets
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234 | echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
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235 | echo 0 > /proc/sys/net/ipv4/conf/default/accept_source_route
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236 |
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237 | # Enable TCP SYN Cookie Protection
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238 | echo 1 > /proc/sys/net/ipv4/tcp_syncookies
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239 |
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240 | # Disable ICMP Redirect Acceptance
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241 | echo 0 > /proc/sys/net/ipv4/conf/default/accept_redirects
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242 |
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243 | # Do not send Redirect Messages
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244 | echo 0 > /proc/sys/net/ipv4/conf/all/send_redirects
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245 | echo 0 > /proc/sys/net/ipv4/conf/default/send_redirects
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246 |
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247 | # Drop Spoofed Packets coming in on an interface, where responses
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248 | # would result in the reply going out a different interface.
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249 | echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter
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250 | echo 1 > /proc/sys/net/ipv4/conf/default/rp_filter
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251 |
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252 | # Log packets with impossible addresses.
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253 | echo 1 > /proc/sys/net/ipv4/conf/all/log_martians
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254 | echo 1 > /proc/sys/net/ipv4/conf/default/log_martians
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255 |
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256 | # be verbose on dynamic ip-addresses (not needed in case of static IP)
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257 | echo 2 > /proc/sys/net/ipv4/ip_dynaddr
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258 |
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259 | # disable Explicit Congestion Notification
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260 | # too many routers are still ignorant
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261 | echo 0 > /proc/sys/net/ipv4/tcp_ecn
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262 |
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263 | # Set a known state
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264 | iptables -P INPUT DROP
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265 | iptables -P FORWARD DROP
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266 | iptables -P OUTPUT DROP
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267 |
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268 | # These lines are here in case rules are already in place and the
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269 | # script is ever rerun on the fly. We want to remove all rules and
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270 | # pre-existing user defined chains before we implement new rules.
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271 | iptables -F
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272 | iptables -X
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273 | iptables -Z
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274 |
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275 | iptables -t nat -F
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276 |
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277 | # Allow local-only connections
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278 | iptables -A INPUT -i lo -j ACCEPT
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279 |
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280 | # Free output on any interface to any ip for any service
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281 | # (equal to -P ACCEPT)
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282 | iptables -A OUTPUT -j ACCEPT
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283 |
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284 | # Permit answers on already established connections
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285 | # and permit new connections related to established ones
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286 | # (e.g. port mode ftp)
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287 | iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
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288 |
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289 | # Drop any incoming MULTICAST or BROADCAST packet before logging:
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290 | # The box outputs several of them when using netbios or mDNS, and those
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291 | # appear immediately as incoming, which clutters the log.
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292 | iptables -A INPUT -m addrtype --dst-type BROADCAST,MULTICAST -j DROP
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293 |
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294 | # Log everything else.
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295 | iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
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296 |
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297 | # End $rc_base/rc.iptables</literal>
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298 | EOF
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299 | chmod 700 /etc/rc.d/rc.iptables</userinput></screen>
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300 |
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301 | <screen role="root" revision="systemd"><?dbfo keep-together="auto"?><userinput>install -v -dm755 /etc/systemd/scripts
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302 |
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303 | cat > /etc/systemd/scripts/iptables << "EOF"
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304 | <literal>#!/bin/sh
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305 |
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306 | # Begin /etc/systemd/scripts/iptables
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307 |
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308 | # Insert connection-tracking modules
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309 | # (not needed if built into the kernel)
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310 | modprobe nf_conntrack
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311 | modprobe xt_LOG
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312 |
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313 | # Enable broadcast echo Protection
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314 | echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
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315 |
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316 | # Disable Source Routed Packets
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317 | echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
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318 | echo 0 > /proc/sys/net/ipv4/conf/default/accept_source_route
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319 |
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320 | # Enable TCP SYN Cookie Protection
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321 | echo 1 > /proc/sys/net/ipv4/tcp_syncookies
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322 |
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323 | # Disable ICMP Redirect Acceptance
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324 | echo 0 > /proc/sys/net/ipv4/conf/default/accept_redirects
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325 |
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326 | # Do not send Redirect Messages
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327 | echo 0 > /proc/sys/net/ipv4/conf/all/send_redirects
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328 | echo 0 > /proc/sys/net/ipv4/conf/default/send_redirects
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329 |
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330 | # Drop Spoofed Packets coming in on an interface, where responses
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331 | # would result in the reply going out a different interface.
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332 | echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter
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333 | echo 1 > /proc/sys/net/ipv4/conf/default/rp_filter
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334 |
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335 | # Log packets with impossible addresses.
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336 | echo 1 > /proc/sys/net/ipv4/conf/all/log_martians
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337 | echo 1 > /proc/sys/net/ipv4/conf/default/log_martians
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338 |
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339 | # be verbose on dynamic ip-addresses (not needed in case of static IP)
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340 | echo 2 > /proc/sys/net/ipv4/ip_dynaddr
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341 |
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342 | # disable Explicit Congestion Notification
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343 | # too many routers are still ignorant
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344 | echo 0 > /proc/sys/net/ipv4/tcp_ecn
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345 |
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346 | # Set a known state
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347 | iptables -P INPUT DROP
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348 | iptables -P FORWARD DROP
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349 | iptables -P OUTPUT DROP
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350 |
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351 | # These lines are here in case rules are already in place and the
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352 | # script is ever rerun on the fly. We want to remove all rules and
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353 | # pre-existing user defined chains before we implement new rules.
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354 | iptables -F
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355 | iptables -X
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356 | iptables -Z
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357 |
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358 | iptables -t nat -F
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359 |
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360 | # Allow local-only connections
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361 | iptables -A INPUT -i lo -j ACCEPT
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362 |
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363 | # Free output on any interface to any ip for any service
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364 | # (equal to -P ACCEPT)
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365 | iptables -A OUTPUT -j ACCEPT
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366 |
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367 | # Permit answers on already established connections
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368 | # and permit new connections related to established ones
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369 | # (e.g. port mode ftp)
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370 | iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
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371 |
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372 | # Log everything else.
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373 | iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
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374 |
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375 | # End /etc/systemd/scripts/iptables</literal>
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376 | EOF
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377 | chmod 700 /etc/systemd/scripts/iptables</userinput></screen>
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378 |
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379 | <para>
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380 | This script is quite simple, it drops all traffic coming
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381 | into your computer that wasn't initiated from your computer, but
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382 | as long as you are simply surfing the Internet you are unlikely
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383 | to exceed its limits.
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384 | </para>
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385 |
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386 | <para>
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387 | If you frequently encounter certain delays at accessing
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388 | FTP servers, take a look at <xref linkend="fw-BB-4-ipt"/>.
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389 | </para>
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390 |
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391 | <para>
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392 | Even if you have daemons or services running on your system,
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393 | these will be inaccessible everywhere but from your computer itself.
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394 | If you want to allow access to services on your machine, such as
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395 | <command>ssh</command> or <command>ping</command>, take a look at
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396 | <xref linkend="fw-busybox-ipt"/>.
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397 | </para>
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398 |
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399 | </sect3>
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400 |
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401 | <sect3 id="fw-masqRouter-ipt"
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402 | xreflabel="Creating a Masquerading Router With iptables">
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403 | <title>Masquerading Router</title>
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404 |
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405 | <para>
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406 | A Network Firewall has two interfaces, one connected to an
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407 | intranet, in this example <emphasis role="strong">LAN1</emphasis>,
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408 | and one connected to the Internet, here <emphasis
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409 | role="strong">WAN1</emphasis>. To provide the maximum security
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410 | for the firewall itself, make sure that there are no unnecessary
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411 | servers running on it such as <application>X11</application>.
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412 | As a general principle, the firewall itself should not access
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413 | any untrusted service (think of a remote server giving answers that
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414 | makes a daemon on your system crash, or even worse, that implements
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415 | a worm via a buffer-overflow).
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416 | </para>
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417 |
|
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418 | <screen role="root" revision="sysv"><?dbfo keep-together="auto"?><userinput>cat > /etc/rc.d/rc.iptables << "EOF"
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419 | <literal>#!/bin/sh
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420 |
|
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421 | # Begin rc.iptables
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422 |
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423 | echo
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424 | echo "You're using the example configuration for a setup of a firewall"
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425 | echo "from Beyond Linux From Scratch."
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426 | echo "This example is far from being complete, it is only meant"
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427 | echo "to be a reference."
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428 | echo "Firewall security is a complex issue, that exceeds the scope"
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429 | echo "of the configuration rules below."
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430 | echo "You can find additional information"
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431 | echo "about firewalls in Chapter 4 of the BLFS book."
|
---|
432 | echo "https://www.&lfs-domainname;/blfs"
|
---|
433 | echo
|
---|
434 |
|
---|
435 | # Insert iptables modules (not needed if built into the kernel).
|
---|
436 |
|
---|
437 | modprobe nf_conntrack
|
---|
438 | modprobe nf_conntrack_ftp
|
---|
439 | modprobe xt_conntrack
|
---|
440 | modprobe xt_LOG
|
---|
441 | modprobe xt_state
|
---|
442 |
|
---|
443 | # Enable broadcast echo Protection
|
---|
444 | echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
|
---|
445 |
|
---|
446 | # Disable Source Routed Packets
|
---|
447 | echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
|
---|
448 |
|
---|
449 | # Enable TCP SYN Cookie Protection
|
---|
450 | echo 1 > /proc/sys/net/ipv4/tcp_syncookies
|
---|
451 |
|
---|
452 | # Disable ICMP Redirect Acceptance
|
---|
453 | echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
|
---|
454 |
|
---|
455 | # Don't send Redirect Messages
|
---|
456 | echo 0 > /proc/sys/net/ipv4/conf/default/send_redirects
|
---|
457 |
|
---|
458 | # Drop Spoofed Packets coming in on an interface where responses
|
---|
459 | # would result in the reply going out a different interface.
|
---|
460 | echo 1 > /proc/sys/net/ipv4/conf/default/rp_filter
|
---|
461 |
|
---|
462 | # Log packets with impossible addresses.
|
---|
463 | echo 1 > /proc/sys/net/ipv4/conf/all/log_martians
|
---|
464 |
|
---|
465 | # Be verbose on dynamic ip-addresses (not needed in case of static IP)
|
---|
466 | echo 2 > /proc/sys/net/ipv4/ip_dynaddr
|
---|
467 |
|
---|
468 | # Disable Explicit Congestion Notification
|
---|
469 | # Too many routers are still ignorant
|
---|
470 | echo 0 > /proc/sys/net/ipv4/tcp_ecn
|
---|
471 |
|
---|
472 | # Set a known state
|
---|
473 | iptables -P INPUT DROP
|
---|
474 | iptables -P FORWARD DROP
|
---|
475 | iptables -P OUTPUT DROP
|
---|
476 |
|
---|
477 | # These lines are here in case rules are already in place and the
|
---|
478 | # script is ever rerun on the fly. We want to remove all rules and
|
---|
479 | # pre-existing user defined chains before we implement new rules.
|
---|
480 | iptables -F
|
---|
481 | iptables -X
|
---|
482 | iptables -Z
|
---|
483 |
|
---|
484 | iptables -t nat -F
|
---|
485 |
|
---|
486 | # Allow local connections
|
---|
487 | iptables -A INPUT -i lo -j ACCEPT
|
---|
488 | iptables -A OUTPUT -o lo -j ACCEPT
|
---|
489 |
|
---|
490 | # Allow forwarding if the initiated on the intranet
|
---|
491 | iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
|
---|
492 | iptables -A FORWARD ! -i WAN1 -m conntrack --ctstate NEW -j ACCEPT
|
---|
493 |
|
---|
494 | # Do masquerading
|
---|
495 | # (not needed if intranet is not using private ip-addresses)
|
---|
496 | iptables -t nat -A POSTROUTING -o WAN1 -j MASQUERADE
|
---|
497 |
|
---|
498 | # Log everything for debugging
|
---|
499 | # (last of all rules, but before policy rules)
|
---|
500 | iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
|
---|
501 | iptables -A FORWARD -j LOG --log-prefix "FIREWALL:FORWARD "
|
---|
502 | iptables -A OUTPUT -j LOG --log-prefix "FIREWALL:OUTPUT "
|
---|
503 |
|
---|
504 | # Enable IP Forwarding
|
---|
505 | echo 1 > /proc/sys/net/ipv4/ip_forward</literal>
|
---|
506 | EOF
|
---|
507 | chmod 700 /etc/rc.d/rc.iptables</userinput></screen>
|
---|
508 |
|
---|
509 | <screen role="root" revision="systemd"><?dbfo keep-together="auto"?><userinput>install -v -dm755 /etc/systemd/scripts
|
---|
510 |
|
---|
511 | cat > /etc/systemd/scripts/iptables << "EOF"
|
---|
512 | <literal>#!/bin/sh
|
---|
513 |
|
---|
514 | # Begin /etc/systemd/scripts/iptables
|
---|
515 |
|
---|
516 | echo
|
---|
517 | echo "You're using the example configuration for a setup of a firewall"
|
---|
518 | echo "from Beyond Linux From Scratch."
|
---|
519 | echo "This example is far from being complete, it is only meant"
|
---|
520 | echo "to be a reference."
|
---|
521 | echo "Firewall security is a complex issue, that exceeds the scope"
|
---|
522 | echo "of the configuration rules below."
|
---|
523 |
|
---|
524 | echo "You can find additional information"
|
---|
525 | echo "about firewalls in Chapter 4 of the BLFS book."
|
---|
526 | echo "https://www.&lfs-domainname;/blfs"
|
---|
527 | echo
|
---|
528 |
|
---|
529 | # Insert iptables modules (not needed if built into the kernel).
|
---|
530 |
|
---|
531 | modprobe nf_conntrack
|
---|
532 | modprobe nf_conntrack_ftp
|
---|
533 | modprobe xt_conntrack
|
---|
534 | modprobe xt_LOG
|
---|
535 | modprobe xt_state
|
---|
536 |
|
---|
537 | # Enable broadcast echo Protection
|
---|
538 | echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
|
---|
539 |
|
---|
540 | # Disable Source Routed Packets
|
---|
541 | echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
|
---|
542 |
|
---|
543 | # Enable TCP SYN Cookie Protection
|
---|
544 | echo 1 > /proc/sys/net/ipv4/tcp_syncookies
|
---|
545 |
|
---|
546 | # Disable ICMP Redirect Acceptance
|
---|
547 | echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
|
---|
548 |
|
---|
549 | # Don't send Redirect Messages
|
---|
550 | echo 0 > /proc/sys/net/ipv4/conf/default/send_redirects
|
---|
551 |
|
---|
552 | # Drop Spoofed Packets coming in on an interface where responses
|
---|
553 | # would result in the reply going out a different interface.
|
---|
554 | echo 1 > /proc/sys/net/ipv4/conf/default/rp_filter
|
---|
555 |
|
---|
556 | # Log packets with impossible addresses.
|
---|
557 | echo 1 > /proc/sys/net/ipv4/conf/all/log_martians
|
---|
558 |
|
---|
559 | # Be verbose on dynamic ip-addresses (not needed in case of static IP)
|
---|
560 | echo 2 > /proc/sys/net/ipv4/ip_dynaddr
|
---|
561 |
|
---|
562 | # Disable Explicit Congestion Notification
|
---|
563 | # Too many routers are still ignorant
|
---|
564 | echo 0 > /proc/sys/net/ipv4/tcp_ecn
|
---|
565 |
|
---|
566 | # Set a known state
|
---|
567 | iptables -P INPUT DROP
|
---|
568 | iptables -P FORWARD DROP
|
---|
569 | iptables -P OUTPUT DROP
|
---|
570 |
|
---|
571 | # These lines are here in case rules are already in place and the
|
---|
572 | # script is ever rerun on the fly. We want to remove all rules and
|
---|
573 | # pre-existing user defined chains before we implement new rules.
|
---|
574 | iptables -F
|
---|
575 | iptables -X
|
---|
576 | iptables -Z
|
---|
577 |
|
---|
578 | iptables -t nat -F
|
---|
579 |
|
---|
580 | # Allow local connections
|
---|
581 | iptables -A INPUT -i lo -j ACCEPT
|
---|
582 | iptables -A OUTPUT -o lo -j ACCEPT
|
---|
583 |
|
---|
584 | # Allow forwarding if the initiated on the intranet
|
---|
585 | iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
|
---|
586 | iptables -A FORWARD ! -i WAN1 -m conntrack --ctstate NEW -j ACCEPT
|
---|
587 |
|
---|
588 | # Do masquerading
|
---|
589 | # (not needed if intranet is not using private ip-addresses)
|
---|
590 | iptables -t nat -A POSTROUTING -o WAN1 -j MASQUERADE
|
---|
591 |
|
---|
592 | # Log everything for debugging
|
---|
593 | # (last of all rules, but before policy rules)
|
---|
594 | iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
|
---|
595 | iptables -A FORWARD -j LOG --log-prefix "FIREWALL:FORWARD "
|
---|
596 | iptables -A OUTPUT -j LOG --log-prefix "FIREWALL:OUTPUT "
|
---|
597 |
|
---|
598 | # Enable IP Forwarding
|
---|
599 | echo 1 > /proc/sys/net/ipv4/ip_forward
|
---|
600 |
|
---|
601 | # The following sections allow inbound packets for specific examples
|
---|
602 | # Uncomment the example lines and adjust as necessary
|
---|
603 |
|
---|
604 | # Allow ping on the external interface
|
---|
605 | #iptables -A INPUT -p icmp -m icmp --icmp-type echo-request -j ACCEPT
|
---|
606 | #iptables -A OUTPUT -p icmp -m icmp --icmp-type echo-reply -j ACCEPT
|
---|
607 |
|
---|
608 | # Reject ident packets with TCP reset to avoid delays with FTP or IRC
|
---|
609 | #iptables -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset
|
---|
610 |
|
---|
611 | # Allow HTTP and HTTPS to 192.168.0.2
|
---|
612 | #iptables -A PREROUTING -t nat -i WAN1 -p tcp --dport 80 -j DNAT --to 192.168.0.2
|
---|
613 | #iptables -A PREROUTING -t nat -i WAN1 -p tcp --dport 443 -j DNAT --to 192.168.0.2
|
---|
614 | #iptables -A FORWARD -p tcp -d 192.168.0.2 --dport 80 -j ACCEPT
|
---|
615 | #iptables -A FORWARD -p tcp -d 192.168.0.2 --dport 443 -j ACCEPT
|
---|
616 |
|
---|
617 | # End /etc/systemd/scripts/iptables</literal>
|
---|
618 | EOF
|
---|
619 | chmod 700 /etc/systemd/scripts/iptables</userinput></screen>
|
---|
620 |
|
---|
621 | <para>
|
---|
622 | With this script your intranet should be reasonably secure
|
---|
623 | against external attacks. No one should be able to setup a new
|
---|
624 | connection to any internal service and, if it's masqueraded,
|
---|
625 | makes your intranet invisible to the Internet. Furthermore, your
|
---|
626 | firewall should be relatively safe because there are no services
|
---|
627 | running that a cracker could attack.
|
---|
628 | </para>
|
---|
629 |
|
---|
630 | </sect3>
|
---|
631 |
|
---|
632 | <sect3 id="fw-busybox-ipt" xreflabel="Creating a BusyBox With iptables">
|
---|
633 | <title>BusyBox</title>
|
---|
634 |
|
---|
635 | <para>
|
---|
636 | This scenario isn't too different from the <xref
|
---|
637 | linkend="fw-masqRouter-ipt"/>, but additionally offers some
|
---|
638 | services to your intranet. Examples of this can be when
|
---|
639 | you want to administer your firewall from another host on
|
---|
640 | your intranet or use it as a proxy or a name server.
|
---|
641 | </para>
|
---|
642 |
|
---|
643 | <note>
|
---|
644 | <para>
|
---|
645 | Outlining specifically how to protect a server that
|
---|
646 | offers services on the Internet goes far beyond the scope of
|
---|
647 | this document. See the references in <xref linkend="fw-extra-info"/>
|
---|
648 | for more information.
|
---|
649 | </para>
|
---|
650 | </note>
|
---|
651 |
|
---|
652 | <para>
|
---|
653 | Be cautious. Every service you have enabled makes your
|
---|
654 | setup more complex and your firewall less secure. You are
|
---|
655 | exposed to the risks of misconfigured services or running
|
---|
656 | a service with an exploitable bug. A firewall should generally
|
---|
657 | not run any extra services. See the introduction to the
|
---|
658 | <xref linkend="fw-masqRouter-ipt"/> for some more details.
|
---|
659 | </para>
|
---|
660 |
|
---|
661 | <para>
|
---|
662 | If you want to add services such as internal Samba or
|
---|
663 | name servers that do not need to access the Internet themselves,
|
---|
664 | the additional statements are quite simple and should still be
|
---|
665 | acceptable from a security standpoint. Just add the following lines
|
---|
666 | into the script <emphasis>before</emphasis> the logging rules.
|
---|
667 | </para>
|
---|
668 |
|
---|
669 | <screen><literal>iptables -A INPUT -i ! WAN1 -j ACCEPT
|
---|
670 | iptables -A OUTPUT -o ! WAN1 -j ACCEPT</literal></screen>
|
---|
671 |
|
---|
672 | <para>
|
---|
673 | If daemons, such as squid, have to access the Internet
|
---|
674 | themselves, you could open OUTPUT generally and restrict
|
---|
675 | INPUT.
|
---|
676 | </para>
|
---|
677 |
|
---|
678 | <screen><literal>iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
|
---|
679 | iptables -A OUTPUT -j ACCEPT</literal></screen>
|
---|
680 |
|
---|
681 | <para>
|
---|
682 | However, it is generally not advisable to leave OUTPUT
|
---|
683 | unrestricted. You lose any control over trojans who would like
|
---|
684 | to "call home", and a bit of redundancy in case you've
|
---|
685 | (mis-)configured a service so that it broadcasts its existence
|
---|
686 | to the world.
|
---|
687 | </para>
|
---|
688 |
|
---|
689 | <para>
|
---|
690 | To accomplish this, you should restrict INPUT and OUTPUT
|
---|
691 | on all ports except those that it's absolutely necessary to have
|
---|
692 | open. Which ports you have to open depends on your needs: mostly
|
---|
693 | you will find them by looking for failed accesses in your log
|
---|
694 | files.
|
---|
695 | </para>
|
---|
696 |
|
---|
697 | <itemizedlist spacing="compact" role='iptables'>
|
---|
698 | <title>Have a Look at the Following Examples:</title>
|
---|
699 | <listitem>
|
---|
700 | <para>
|
---|
701 | Squid is caching the web:
|
---|
702 | </para>
|
---|
703 |
|
---|
704 | <screen><literal>iptables -A OUTPUT -p tcp --dport 80 -j ACCEPT
|
---|
705 | iptables -A INPUT -p tcp --sport 80 -m conntrack --ctstate ESTABLISHED \
|
---|
706 | -j ACCEPT</literal></screen>
|
---|
707 |
|
---|
708 | </listitem>
|
---|
709 | <listitem>
|
---|
710 | <para>
|
---|
711 | Your caching name server (e.g., named) does its lookups via UDP:
|
---|
712 | </para>
|
---|
713 |
|
---|
714 | <screen><literal>iptables -A OUTPUT -p udp --dport 53 -j ACCEPT</literal></screen>
|
---|
715 |
|
---|
716 | </listitem>
|
---|
717 | <listitem>
|
---|
718 | <para>
|
---|
719 | You want to be able to ping your computer to ensure it's still
|
---|
720 | alive:
|
---|
721 | </para>
|
---|
722 |
|
---|
723 | <screen><literal>iptables -A INPUT -p icmp -m icmp --icmp-type echo-request -j ACCEPT
|
---|
724 | iptables -A OUTPUT -p icmp -m icmp --icmp-type echo-reply -j ACCEPT</literal></screen>
|
---|
725 |
|
---|
726 | </listitem>
|
---|
727 | <listitem>
|
---|
728 | <para id='fw-BB-4-ipt' xreflabel="BusyBox with iptables example number 4">
|
---|
729 | If you are frequently accessing FTP servers or enjoy chatting, you
|
---|
730 | might notice delays because some implementations of these daemons
|
---|
731 | query an identd daemon on your system to obtain usernames. Although
|
---|
732 | there's really little harm in this, having an identd running is not
|
---|
733 | recommended because many security experts feel the service gives
|
---|
734 | out too much additional information.
|
---|
735 | </para>
|
---|
736 |
|
---|
737 | <para>
|
---|
738 | To avoid these delays you could reject the requests with a
|
---|
739 | 'tcp-reset' response:
|
---|
740 | </para>
|
---|
741 |
|
---|
742 | <screen><literal>iptables -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset</literal></screen>
|
---|
743 |
|
---|
744 | </listitem>
|
---|
745 | <listitem>
|
---|
746 | <para>
|
---|
747 | To log and drop invalid packets (packets
|
---|
748 | that came in after netfilter's timeout or some types of
|
---|
749 | network scans) insert these rules at the top of the chain:
|
---|
750 | </para>
|
---|
751 |
|
---|
752 | <screen><literal>iptables -I INPUT 0 -p tcp -m conntrack --ctstate INVALID \
|
---|
753 | -j LOG --log-prefix "FIREWALL:INVALID "
|
---|
754 | iptables -I INPUT 1 -p tcp -m conntrack --ctstate INVALID -j DROP</literal></screen>
|
---|
755 |
|
---|
756 | </listitem>
|
---|
757 | <listitem>
|
---|
758 | <para>
|
---|
759 | Anything coming from the outside should not have a
|
---|
760 | private address, this is a common attack called IP-spoofing:
|
---|
761 | </para>
|
---|
762 |
|
---|
763 | <screen><literal>iptables -A INPUT -i WAN1 -s 10.0.0.0/8 -j DROP
|
---|
764 | iptables -A INPUT -i WAN1 -s 172.16.0.0/12 -j DROP
|
---|
765 | iptables -A INPUT -i WAN1 -s 192.168.0.0/16 -j DROP</literal></screen>
|
---|
766 |
|
---|
767 | <para>
|
---|
768 | There are other addresses that you may also want to drop:
|
---|
769 | 0.0.0.0/8, 127.0.0.0/8, 224.0.0.0/3 (multicast and
|
---|
770 | experimental), 169.254.0.0/16 (Link Local Networks), and
|
---|
771 | 192.0.2.0/24 (IANA defined test network).
|
---|
772 | </para>
|
---|
773 | </listitem>
|
---|
774 | <listitem>
|
---|
775 | <para>
|
---|
776 | If your firewall is a DHCP client, you need to allow those packets:
|
---|
777 | </para>
|
---|
778 |
|
---|
779 | <screen><literal>iptables -A INPUT -i WAN1 -p udp -s 0.0.0.0 --sport 67 \
|
---|
780 | -d 255.255.255.255 --dport 68 -j ACCEPT</literal></screen>
|
---|
781 |
|
---|
782 | </listitem>
|
---|
783 | <listitem>
|
---|
784 | <para>
|
---|
785 | To simplify debugging and be fair to anyone who'd like
|
---|
786 | to access a service you have disabled, purposely or by mistake,
|
---|
787 | you could REJECT those packets that are dropped.
|
---|
788 | </para>
|
---|
789 |
|
---|
790 | <para>
|
---|
791 | Obviously this must be done directly after logging as the very
|
---|
792 | last lines before the packets are dropped by policy:
|
---|
793 | </para>
|
---|
794 |
|
---|
795 | <screen><literal>iptables -A INPUT -j REJECT</literal></screen>
|
---|
796 |
|
---|
797 | </listitem>
|
---|
798 | </itemizedlist>
|
---|
799 |
|
---|
800 | <para>
|
---|
801 | These are only examples to show you some of the capabilities
|
---|
802 | of the firewall code in Linux. Have a look at the man page of iptables.
|
---|
803 | There you will find much more information. The port numbers needed for
|
---|
804 | this can be found in <filename>/etc/services</filename>, in case you
|
---|
805 | didn't find them by trial and error in your log file.
|
---|
806 | </para>
|
---|
807 |
|
---|
808 | </sect3>
|
---|
809 |
|
---|
810 | <sect3 id="iptables-init">
|
---|
811 | <title><phrase revision="sysv">Boot Script</phrase>
|
---|
812 | <phrase revision="systemd">Systemd Unit</phrase></title>
|
---|
813 |
|
---|
814 | <para revision="sysv">
|
---|
815 | To set up the iptables firewall at boot, install the
|
---|
816 | <filename>/etc/rc.d/init.d/iptables</filename> init script included
|
---|
817 | in the <xref linkend="bootscripts"/> package.
|
---|
818 | </para>
|
---|
819 |
|
---|
820 | <para revision="systemd">
|
---|
821 | To set up the iptables firewall at boot, install the
|
---|
822 | <filename>iptables.service</filename> unit included in the
|
---|
823 | <xref linkend="systemd-units"/> package.
|
---|
824 | </para>
|
---|
825 |
|
---|
826 | <indexterm zone="iptables iptables-init">
|
---|
827 | <primary sortas="f-iptables">iptables</primary>
|
---|
828 | </indexterm>
|
---|
829 |
|
---|
830 | <screen role="root"><userinput>make install-iptables</userinput></screen>
|
---|
831 |
|
---|
832 | </sect3>
|
---|
833 |
|
---|
834 | </sect2>
|
---|
835 |
|
---|
836 | <sect2 role="content">
|
---|
837 | <title>Contents</title>
|
---|
838 |
|
---|
839 | <segmentedlist>
|
---|
840 | <segtitle>Installed Programs</segtitle>
|
---|
841 | <segtitle>Installed Libraries</segtitle>
|
---|
842 | <segtitle>Installed Directories</segtitle>
|
---|
843 |
|
---|
844 | <seglistitem>
|
---|
845 | <seg>
|
---|
846 | ip6tables,
|
---|
847 | ip6tables-apply,
|
---|
848 | ip6tables-legacy,
|
---|
849 | ip6tables-legacy-restore,
|
---|
850 | ip6tables-legacy-save,
|
---|
851 | ip6tables-restore,
|
---|
852 | ip6tables-save,
|
---|
853 | iptables,
|
---|
854 | iptables-apply,
|
---|
855 | iptables-legacy,
|
---|
856 | iptables-legacy-restore,
|
---|
857 | iptables-legacy-apply,
|
---|
858 | iptables-restore,
|
---|
859 | iptables-save,
|
---|
860 | iptables-xml,
|
---|
861 | nfsynproxy (optional),
|
---|
862 | and xtables-multi
|
---|
863 | </seg>
|
---|
864 | <seg>
|
---|
865 | libip4tc.so,
|
---|
866 | libip6tc.so,
|
---|
867 | libipq.so,
|
---|
868 | libiptc.so,
|
---|
869 | and libxtables.so
|
---|
870 | </seg>
|
---|
871 | <seg>
|
---|
872 | /lib/xtables and
|
---|
873 | /usr/include/libiptc
|
---|
874 | </seg>
|
---|
875 | </seglistitem>
|
---|
876 | </segmentedlist>
|
---|
877 |
|
---|
878 | <variablelist>
|
---|
879 | <bridgehead renderas="sect3">Short Descriptions</bridgehead>
|
---|
880 | <?dbfo list-presentation="list"?>
|
---|
881 | <?dbhtml list-presentation="table"?>
|
---|
882 |
|
---|
883 | <varlistentry id="iptables-prog">
|
---|
884 | <term><command>iptables</command></term>
|
---|
885 | <listitem>
|
---|
886 | <para>
|
---|
887 | is used to set up, maintain, and inspect the tables of
|
---|
888 | IP packet filter rules in the Linux kernel
|
---|
889 | </para>
|
---|
890 | <indexterm zone="iptables iptables-prog">
|
---|
891 | <primary sortas="b-iptables">iptables</primary>
|
---|
892 | </indexterm>
|
---|
893 | </listitem>
|
---|
894 | </varlistentry>
|
---|
895 |
|
---|
896 | <varlistentry id="iptables-apply">
|
---|
897 | <term><command>iptables-apply</command></term>
|
---|
898 | <listitem>
|
---|
899 | <para>
|
---|
900 | is a safer way to update iptables remotely
|
---|
901 | </para>
|
---|
902 | <indexterm zone="iptables iptables-apply">
|
---|
903 | <primary sortas="b-iptables-apply">iptables-apply</primary>
|
---|
904 | </indexterm>
|
---|
905 | </listitem>
|
---|
906 | </varlistentry>
|
---|
907 |
|
---|
908 | <varlistentry id="iptables-legacy">
|
---|
909 | <term><command>iptables-legacy</command></term>
|
---|
910 | <listitem>
|
---|
911 | <para>
|
---|
912 | is used to interact with iptables using the legacy command set
|
---|
913 | </para>
|
---|
914 | <indexterm zone="iptables iptables-legacy">
|
---|
915 | <primary sortas="b-iptables-legacy">iptables-legacy</primary>
|
---|
916 | </indexterm>
|
---|
917 | </listitem>
|
---|
918 | </varlistentry>
|
---|
919 |
|
---|
920 | <varlistentry id="iptables-legacy-restore">
|
---|
921 | <term><command>iptables-legacy-restore</command></term>
|
---|
922 | <listitem>
|
---|
923 | <para>
|
---|
924 | is used to restore a set of legacy iptables rules
|
---|
925 | </para>
|
---|
926 | <indexterm zone="iptables iptables-legacy-restore">
|
---|
927 | <primary sortas="b-iptables-legacy-restore">iptables-legacy-restore</primary>
|
---|
928 | </indexterm>
|
---|
929 | </listitem>
|
---|
930 | </varlistentry>
|
---|
931 |
|
---|
932 | <varlistentry id="iptables-legacy-save">
|
---|
933 | <term><command>iptables-legacy-save</command></term>
|
---|
934 | <listitem>
|
---|
935 | <para>
|
---|
936 | is used to save a set of legacy iptables rules
|
---|
937 | </para>
|
---|
938 | <indexterm zone="iptables iptables-legacy-save">
|
---|
939 | <primary sortas="b-iptables-legacy-save">iptables-legacy-save</primary>
|
---|
940 | </indexterm>
|
---|
941 | </listitem>
|
---|
942 | </varlistentry>
|
---|
943 |
|
---|
944 | <varlistentry id="iptables-restore">
|
---|
945 | <term><command>iptables-restore</command></term>
|
---|
946 | <listitem>
|
---|
947 | <para>
|
---|
948 | is used to restore IP Tables from data specified on
|
---|
949 | STDIN. Use I/O redirection provided by your
|
---|
950 | shell to read from a file
|
---|
951 | </para>
|
---|
952 | <indexterm zone="iptables iptables-restore">
|
---|
953 | <primary sortas="b-iptables-restore">iptables-restore</primary>
|
---|
954 | </indexterm>
|
---|
955 | </listitem>
|
---|
956 | </varlistentry>
|
---|
957 |
|
---|
958 | <varlistentry id="iptables-save">
|
---|
959 | <term><command>iptables-save</command></term>
|
---|
960 | <listitem>
|
---|
961 | <para>
|
---|
962 | is used to dump the contents of an IP Table in easily
|
---|
963 | parseable format to STDOUT. Use I/O-redirection
|
---|
964 | provided by your shell to write to a file
|
---|
965 | </para>
|
---|
966 | <indexterm zone="iptables iptables-save">
|
---|
967 | <primary sortas="b-iptables-save">iptables-save</primary>
|
---|
968 | </indexterm>
|
---|
969 | </listitem>
|
---|
970 | </varlistentry>
|
---|
971 |
|
---|
972 | <varlistentry id="iptables-xml">
|
---|
973 | <term><command>iptables-xml</command></term>
|
---|
974 | <listitem>
|
---|
975 | <para>
|
---|
976 | is used to convert the output of
|
---|
977 | <command>iptables-save</command> to an XML format. Using the
|
---|
978 | <filename>iptables.xslt</filename> stylesheet converts the XML
|
---|
979 | back to the format of <command>iptables-restore</command>
|
---|
980 | </para>
|
---|
981 | <indexterm zone="iptables iptables-xml">
|
---|
982 | <primary sortas="b-iptables-xml">iptables-xml</primary>
|
---|
983 | </indexterm>
|
---|
984 | </listitem>
|
---|
985 | </varlistentry>
|
---|
986 |
|
---|
987 | <varlistentry id="ip6tables">
|
---|
988 | <term><command>ip6tables*</command></term>
|
---|
989 | <listitem>
|
---|
990 | <para>
|
---|
991 | are a set of commands for IPV6 that parallel the iptables
|
---|
992 | commands above
|
---|
993 | </para>
|
---|
994 | <indexterm zone="iptables ip6tables">
|
---|
995 | <primary sortas="b-ip6tables">ip6tables</primary>
|
---|
996 | </indexterm>
|
---|
997 | </listitem>
|
---|
998 | </varlistentry>
|
---|
999 |
|
---|
1000 | <varlistentry id="nfsynproxy">
|
---|
1001 | <term><command>nfsynproxy</command></term>
|
---|
1002 | <listitem>
|
---|
1003 | <para>
|
---|
1004 | (optional) configuration tool. SYNPROXY target makes handling of
|
---|
1005 | large SYN floods possible without the large performance penalties
|
---|
1006 | imposed by the connection tracking in such cases
|
---|
1007 | </para>
|
---|
1008 | <indexterm zone="iptables nfsynproxy">
|
---|
1009 | <primary sortas="b-nfsynproxy">nfsynproxy</primary>
|
---|
1010 | </indexterm>
|
---|
1011 | </listitem>
|
---|
1012 | </varlistentry>
|
---|
1013 |
|
---|
1014 | <varlistentry id="xtables-multi">
|
---|
1015 | <term><command>xtables-multi</command></term>
|
---|
1016 | <listitem>
|
---|
1017 | <para>
|
---|
1018 | is a binary that behaves according to the name it is called by
|
---|
1019 | </para>
|
---|
1020 | <indexterm zone="iptables xtables-multi">
|
---|
1021 | <primary sortas="b-xtables-multi">xtables-multi</primary>
|
---|
1022 | </indexterm>
|
---|
1023 | </listitem>
|
---|
1024 | </varlistentry>
|
---|
1025 |
|
---|
1026 | </variablelist>
|
---|
1027 |
|
---|
1028 | </sect2>
|
---|
1029 |
|
---|
1030 | </sect1>
|
---|