source: chapter07/network.xml@ 0090db5

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<sect1 id="ch-scripts-network">
  <?dbhtml filename="network.html"?>

  <title>Configuring the network Script</title>

  <indexterm zone="ch-scripts-network">
    <primary sortas="d-network">network</primary>
  <secondary>configuring</secondary></indexterm>

  <para>This section only applies if a network card is to be
  configured.</para>

  <para>If a network card will not be used, there is likely no need to
  create any configuration files relating to network cards. If that is
  the case, remove the <filename class="symlink">network</filename>
  symlinks from all run-level directories (<filename
  class="directory">/etc/rc.d/rc*.d</filename>).</para>

  <sect2>
    <title>Creating stable names for network interfaces</title>

    <para>Instructions in this section are optional if you have only one
    network card.</para>

    <para>With Udev and modular network drivers, the network interface numbering
    is not persistent across reboots by default, because the drivers are loaded
    in parallel and, thus, in random order. For example, on a computer having
    two network cards made by Intel and Realtek, the network card manufactured
    by Intel may become <filename class="devicefile">eth0</filename> and the
    Realtek card becomes  <filename class="devicefile">eth1</filename>. In some
    cases, after a reboot the cards get renumbered the other way around. To
    avoid this, create Udev rules that assign stable names to network cards
    based on their MAC addresses.</para>

    <para>First, find out the MAC addresses of your network cards:</para>

<screen role="nodump"><userinput>grep -H . /sys/class/net/*/address</userinput></screen>

    <para>For each network card (but not for the loopback interface),
    invent a descriptive name, such as <quote>realtek</quote>, and create
    Udev rules similar to the following:</para>

<screen role="nodump"><userinput>cat &gt; /etc/udev/rules.d/26-network.rules &lt;&lt; "EOF"
<literal>ACTION=="add", SUBSYSTEM=="net", SYSFS{address}=="<replaceable>52:54:00:12:34:56</replaceable>", NAME="<replaceable>realtek</replaceable>"
ACTION=="add", SUBSYSTEM=="net", SYSFS{address}=="<replaceable>00:a0:c9:78:9a:bc</replaceable>", NAME="<replaceable>intel</replaceable>"</literal>
EOF</userinput></screen>

    <para>These rules will always rename the network cards to
    <quote>realtek</quote> and <quote>intel</quote>, independently of the
    original numbering provided by the kernel. Use these names instead of
    <quote>eth0</quote> in the network interface configuration files created
    below.</para>

    <note>
      <para>Persistent names must be different from the default network
      interface names assigned by the kernel.</para>
    </note>

  </sect2>

  <sect2>
    <title>Creating Network Interface Configuration Files</title>

    <para>Which interfaces are brought up and down by the network script
    depends on the files and directories in the <filename
    class="directory">/etc/sysconfig/network-devices</filename> hierarchy.
    This directory should contain a sub-directory for each interface to be
    configured, such as <filename>ifconfig.xyz</filename>, where
    <quote>xyz</quote> is a network interface name. Inside this directory
    would be files defining the attributes to this interface, such as its IP
    address(es), subnet masks, and so forth.</para>

    <para>The following command creates a sample <filename>ipv4</filename>
    file for the <emphasis>eth0</emphasis> device:</para>

<screen><userinput>cd /etc/sysconfig/network-devices &amp;&amp;
mkdir -v ifconfig.eth0 &amp;&amp;
cat &gt; ifconfig.eth0/ipv4 &lt;&lt; "EOF"
<literal>ONBOOT=yes
SERVICE=ipv4-static
IP=192.168.1.1
GATEWAY=192.168.1.2
PREFIX=24
BROADCAST=192.168.1.255</literal>
EOF</userinput></screen>

    <para>The values of these variables must be changed in every file to match
    the proper setup. If the <envar>ONBOOT</envar> variable is set to
    <quote>yes</quote> the network script will bring up the Network Interface
    Card (NIC) during booting of the system. If set to anything but
    <quote>yes</quote> the NIC will be ignored by the network script and not
    be brought up.</para>

    <para>The <envar>SERVICE</envar> variable defines the method used for
    obtaining the IP address. The LFS-Bootscripts package has a modular IP
    assignment format, and creating additional files in the <filename
    class="directory">/etc/sysconfig/network-devices/services</filename>
    directory allows other IP assignment methods. This is commonly used for
    Dynamic Host Configuration Protocol (DHCP), which is addressed in the
    BLFS book.</para>

    <para>The <envar>GATEWAY</envar> variable should contain the default
    gateway IP address, if one is present. If not, then comment out the
    variable entirely.</para>

    <para>The <envar>PREFIX</envar> variable needs to contain the number of
    bits used in the subnet. Each octet in an IP address is 8 bits. If the
    subnet's netmask is 255.255.255.0, then it is using the first three octets
    (24 bits) to specify the network number. If the netmask is 255.255.255.240,
    it would be using the first 28 bits.  Prefixes longer than 24 bits are
    commonly used by DSL and cable-based Internet Service Providers (ISPs).
    In this example (PREFIX=24), the netmask is 255.255.255.0. Adjust the
    <envar>PREFIX</envar> variable according to your specific subnet.</para>

  </sect2>

  <sect2 id="resolv.conf">
    <title>Creating the /etc/resolv.conf File</title>

    <indexterm zone="resolv.conf">
      <primary sortas="e-/etc/resolv.conf">/etc/resolv.conf</primary>
    </indexterm>

    <para>If the system is going to be connected to the Internet, it will
    need some means of Domain Name Service (DNS) name resolution to
    resolve Internet domain names to IP addresses, and vice versa. This is
    best achieved by placing the IP address of the DNS server, available
    from the ISP or network administrator, into
    <filename>/etc/resolv.conf</filename>. Create the file by running the
    following:</para>

<screen><userinput>cat &gt; /etc/resolv.conf &lt;&lt; "EOF"
<literal># Begin /etc/resolv.conf

domain {<replaceable>&lt;Your Domain Name&gt;</replaceable>}
nameserver <replaceable>&lt;IP address of your primary nameserver&gt;</replaceable>
nameserver <replaceable>&lt;IP address of your secondary nameserver&gt;</replaceable>

# End /etc/resolv.conf</literal>
EOF</userinput></screen>

    <para>Replace <replaceable>&lt;IP address of the nameserver&gt;</replaceable>
    with the IP address of the DNS most appropriate for the setup. There will
    often be more than one entry (requirements demand secondary servers for
    fallback capability). If you only need or want one DNS server, remove the
    second <emphasis>nameserver</emphasis> line from the file. The IP address
    may also be a router on the local network.</para>

  </sect2>

</sect1>