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 |
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8 | <sect1 id="ch-scripts-network">
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9 | <?dbhtml filename="network.html"?>
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10 |
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11 | <title>General Network Configuration</title>
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12 |
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13 | <indexterm zone="ch-scripts-network">
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14 | <primary sortas="d-network">network</primary>
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15 | <secondary>configuring</secondary></indexterm>
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16 |
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17 | <para>This section only applies if a network card is to be
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18 | configured.</para>
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19 |
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20 | <para>If a network card will not be used, there is likely no need to
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21 | create any configuration files relating to network cards. If that is
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22 | the case, remove the <filename class="symlink">network</filename>
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23 | symlinks from all run-level directories (<filename
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24 | class="directory">/etc/rc.d/rc*.d</filename>).</para>
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25 |
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26 | <sect2>
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27 | <title>Creating stable names for network interfaces</title>
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28 |
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29 | <para>If there is only one network interface in the system to be
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30 | configured, this section is optional, although it will never be wrong to do
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31 | it. In many cases (e.g. a laptop with a wireless and a wired interface),
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32 | accomplishing the configuration in this section is necessary.</para>
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33 |
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34 | <para>With Udev and modular network drivers, the network interface numbering
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35 | is not persistent across reboots by default, because the drivers are loaded
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36 | in parallel and, thus, in random order. For example, on a computer having
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37 | two network cards made by Intel and Realtek, the network card manufactured
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38 | by Intel may become <filename class="devicefile">eth0</filename> and the
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39 | Realtek card becomes <filename class="devicefile">eth1</filename>. In some
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40 | cases, after a reboot the cards get renumbered the other way around. To
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41 | avoid this, Udev comes with a script and some rules to assign stable names
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42 | to network cards based on their MAC address.</para>
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43 |
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44 | <para>Pre-generate the rules to ensure the same names get assigned to the
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45 | same devices at every boot, including the first:</para>
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46 |
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47 | <screen><userinput>for NIC in /sys/class/net/* ; do
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48 | INTERFACE=${NIC##*/} udevadm test --action=add $NIC
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49 | done</userinput></screen>
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50 |
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51 | <para>Now, inspect the <filename>/etc/udev/rules.d/70-persistent-net.rules</filename>
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52 | file, to find out which name was assigned to which network device:</para>
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53 |
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54 | <screen role="nodump"><userinput>cat /etc/udev/rules.d/70-persistent-net.rules</userinput></screen>
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55 |
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56 | <para>The file begins with a comment block followed by two lines for each
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57 | NIC. The first line for each NIC is a commented description showing its
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58 | hardware IDs (e.g. its PCI vendor and device IDs, if it's a PCI card),
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59 | along with its driver in parentheses, if the driver can be found. Neither
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60 | the hardware ID nor the driver is used to determine which name to give an
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61 | interface; this information is only for reference. The second line is the
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62 | Udev rule that matches this NIC and actually assigns it a name.</para>
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63 |
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64 | <para>All Udev rules are made up of several keys, separated by commas and
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65 | optional whitespace. This rule's keys and an explanation of each of them
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66 | are as follows:</para>
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67 |
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68 | <itemizedlist>
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69 | <listitem>
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70 | <para><literal>SUBSYSTEM=="net"</literal> - This tells Udev to ignore
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71 | devices that are not network cards.</para>
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72 | </listitem>
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73 | <listitem>
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74 | <para><literal>ACTION=="add"</literal> - This tells Udev to ignore this
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75 | rule for a uevent that isn't an add ("remove" and "change" uevents also
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76 | happen, but don't need to rename network interfaces).</para>
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77 | </listitem>
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78 | <listitem>
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79 | <para><literal>DRIVERS=="?*"</literal> - This exists so that Udev will
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80 | ignore VLAN or bridge sub-interfaces (because these sub-interfaces do
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81 | not have drivers). These sub-interfaces are skipped because the name
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82 | that would be assigned would collide with their parent devices.</para>
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83 | </listitem>
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84 | <listitem>
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85 | <para><literal>ATTR{address}</literal> - The value of this key is the
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86 | NIC's MAC address.</para>
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87 | </listitem>
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88 | <listitem>
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89 | <para><literal>ATTR{type}=="1"</literal> - This ensures the rule only
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90 | matches the primary interface in the case of certain wireless drivers,
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91 | which create multiple virtual interfaces. The secondary interfaces are
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92 | skipped for the same reason that VLAN and bridge sub-interfaces are
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93 | skipped: there would be a name collision otherwise.</para>
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94 | </listitem>
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95 | <listitem>
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96 | <para><literal>KERNEL=="eth*"</literal> - This key was added to the
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97 | Udev rule generator to handle machines that have multiple network
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98 | interfaces, all with the same MAC address (the PS3 is one such
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99 | machine). If the independent interfaces have different basenames,
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100 | this key will allow Udev to tell them apart. This is generally not
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101 | necessary for most Linux From Scratch users, but does not hurt.</para>
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102 | </listitem>
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103 | <listitem>
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104 | <para><literal>NAME</literal> - The value of this key is the name that
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105 | Udev will assign to this interface.</para>
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106 | </listitem>
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107 | </itemizedlist>
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108 |
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109 | <para>The value of <literal>NAME</literal> is the important part. Make sure
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110 | you know which name has been assigned to each of your network cards before
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111 | proceeding, and be sure to use that <literal>NAME</literal> value when
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112 | creating your configuration files below.</para>
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113 |
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114 | </sect2>
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115 |
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116 | <sect2>
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117 | <title>Creating Network Interface Configuration Files</title>
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118 |
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119 | <para>Which interfaces are brought up and down by the network script
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120 | depends on the files in <filename
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121 | class="directory">/etc/sysconfig/</filename>. This directory should
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122 | contain a file for each interface to be configured, such as
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123 | <filename>ifconfig.xyz</filename>, where <quote>xyz</quote> is
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124 | meaningful to the administrator such as the device name (e.g. eth0).
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125 | Inside this file are attributes to this interface, such as its IP
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126 | address(es), subnet masks, and so forth. It is necessary that
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127 | the stem of the filename be <emphasis>ifconfig</emphasis>.</para>
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128 |
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129 | <para>The following command creates a sample file for the
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130 | <emphasis>eth0</emphasis> device with a static IP address:</para>
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131 |
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132 | <screen><userinput>cd /etc/sysconfig/
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133 | cat > ifconfig.eth0 << "EOF"
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134 | <literal>ONBOOT=yes
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135 | IFACE=eth0
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136 | SERVICE=ipv4-static
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137 | IP=192.168.1.1
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138 | GATEWAY=192.168.1.2
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139 | PREFIX=24
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140 | BROADCAST=192.168.1.255</literal>
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141 | EOF</userinput></screen>
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142 |
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143 | <para>The values of these variables must be changed in every file to match
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144 | the proper setup.</para>
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145 |
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146 | <para>If the <envar>ONBOOT</envar> variable is set to <quote>yes</quote> the
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147 | network script will bring up the Network Interface Card (NIC) during
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148 | booting of the system. If set to anything but <quote>yes</quote> the NIC
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149 | will be ignored by the network script and not be automatically brought up.
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150 | The interface can be manually started or stopped with the
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151 | <command>ifup</command> and <command>ifdown</command> commands.</para>
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152 |
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153 | <para>The <envar>IFACE</envar> variable defines the interface name,
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154 | for example, eth0. It is required for all network device configuration
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155 | files. </para>
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156 |
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157 | <para>The <envar>SERVICE</envar> variable defines the method used for
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158 | obtaining the IP address. The LFS-Bootscripts package has a modular IP
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159 | assignment format, and creating additional files in the <filename
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160 | class="directory">/lib/services/</filename> directory allows other IP
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161 | assignment methods. This is commonly used for Dynamic Host Configuration
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162 | Protocol (DHCP), which is addressed in the BLFS book.</para>
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163 |
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164 | <para>The <envar>GATEWAY</envar> variable should contain the default
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165 | gateway IP address, if one is present. If not, then comment out the
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166 | variable entirely.</para>
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167 |
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168 | <para>The <envar>PREFIX</envar> variable contains the number of
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169 | bits used in the subnet. Each octet in an IP address is 8 bits. If the
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170 | subnet's netmask is 255.255.255.0, then it is using the first three octets
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171 | (24 bits) to specify the network number. If the netmask is 255.255.255.240,
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172 | it would be using the first 28 bits. Prefixes longer than 24 bits are
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173 | commonly used by DSL and cable-based Internet Service Providers (ISPs).
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174 | In this example (PREFIX=24), the netmask is 255.255.255.0. Adjust the
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175 | <envar>PREFIX</envar> variable according to your specific subnet.i
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176 | If omitted, the PREFIX defaults to 24.</para>
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177 |
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178 | <para>For more information see the <command>ifup</command> man page.</para>
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179 |
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180 | </sect2>
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181 |
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182 | <sect2 id="resolv.conf">
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183 | <title>Creating the /etc/resolv.conf File</title>
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184 |
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185 | <indexterm zone="resolv.conf">
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186 | <primary sortas="e-/etc/resolv.conf">/etc/resolv.conf</primary>
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187 | </indexterm>
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188 |
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189 | <para>If the system is going to be connected to the Internet, it will
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190 | need some means of Domain Name Service (DNS) name resolution to
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191 | resolve Internet domain names to IP addresses, and vice versa. This is
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192 | best achieved by placing the IP address of the DNS server, available
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193 | from the ISP or network administrator, into
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194 | <filename>/etc/resolv.conf</filename>. Create the file by running the
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195 | following:</para>
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196 |
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197 | <screen><userinput>cat > /etc/resolv.conf << "EOF"
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198 | <literal># Begin /etc/resolv.conf
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199 |
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200 | domain <replaceable><Your Domain Name></replaceable>
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201 | nameserver <replaceable><IP address of your primary nameserver></replaceable>
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202 | nameserver <replaceable><IP address of your secondary nameserver></replaceable>
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203 |
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204 | # End /etc/resolv.conf</literal>
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205 | EOF</userinput></screen>
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206 |
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207 | <para>The <varname>domain</varname> statement can be omitted
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208 | or replaced with a <varname>search</varname> statement. See the man page for
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209 | resolv.conf for more details.</para>
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210 |
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211 | <para>Replace <replaceable><IP address of the nameserver></replaceable>
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212 | with the IP address of the DNS most appropriate for the setup. There will
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213 | often be more than one entry (requirements demand secondary servers for
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214 | fallback capability). If you only need or want one DNS server, remove the
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215 | second <emphasis>nameserver</emphasis> line from the file. The IP address
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216 | may also be a router on the local network.</para>
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217 |
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218 | <note><para>The Google Public IPv4 DNS addresses are 8.8.8.8 and 8.8.4.4.</para></note>
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219 |
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220 | </sect2>
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221 |
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222 | </sect1>
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