lfs-book/chapter07/network.xml

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

  <title>General Network Configuration</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>

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

    <para>Which interfaces are brought up and down by the network script
    depends on the files in <filename
    class="directory">/etc/sysconfig/</filename>.  This directory should
    contain a file for each interface to be configured, such as
    <filename>ifconfig.xyz</filename>, where <quote>xyz</quote> is
    meaningful to the administrator such as the device name (e.g. eth0).
    Inside this file are attributes to this interface, such as its IP
    address(es), subnet masks, and so forth.  It is necessary that
    the stem of the filename be <emphasis>ifconfig</emphasis>.</para>

    <para>The following command creates a sample file for the
    <emphasis>eth0</emphasis> device with a static IP address:</para>

<screen><userinput>cd /etc/sysconfig/
cat &gt; ifconfig.eth0 &lt;&lt; "EOF"
<literal>ONBOOT=yes
IFACE=eth0
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.</para>

    <para>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 automatically brought up.
    The interface can be manually started or stopped with the
    <command>ifup</command> and <command>ifdown</command> commands.</para>

    <para>The <envar>IFACE</envar> variable defines the interface name,
    for example, eth0.  It is required for all network device configuration
    files. </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">/lib/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 contains 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.
    If omitted, the PREFIX defaults to 24.</para>

    <para>For more information see the <command>ifup</command> man page.</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>The <varname>domain</varname> statement can be omitted
    or replaced with a <varname>search</varname> statement.  See the man page for
    resolv.conf for more details.</para>

    <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>

    <note><para>The Google Public IPv4 DNS addresses are 8.8.8.8 and 8.8.4.4.</para></note>

  </sect2>

</sect1>