source: chapter07/network.xml@ 966b175

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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 or bus positions.</para>

    <para>If you are going to use MAC addresses to identify your network
    cards, find the addresses with the following command:</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", DRIVER=="?*", SYSFS{address}=="<replaceable>00:e0:4c:12:34:56</replaceable>", NAME="<replaceable>realtek</replaceable>"
ACTION=="add", SUBSYSTEM=="net", DRIVER=="?*", SYSFS{address}=="<replaceable>00:a0:c9:78:9a:bc</replaceable>", NAME="<replaceable>intel</replaceable>"</literal>
EOF</userinput></screen>

    <para>The DRIVER=="?*" key prevents Udev from attempting to rename 8021Q
    VLAN interfaces (not available without the Vlan package from
    <ulink url="http://www.candelatech.com/~greear/vlan/"/>).
    This is necessary since VLANs have the same MAC address as
    the real network card.</para>

<!-- Yes, I know that VLANs are beyond BLFS. This is not the reason to get them
     incorrect by default when every distro does this right. -->
 
    <para>If you are going to use the bus position as a key, 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", BUS=="<replaceable>pci</replaceable>", ID=="<replaceable>0000:00:0c.0</replaceable>", NAME="<replaceable>realtek</replaceable>"
ACTION=="add", SUBSYSTEM=="net", BUS=="<replaceable>pci</replaceable>", ID=="<replaceable>0000:00:0d.0</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 (i.e.: the original
    <quote>eth0</quote> and <quote>eth1</quote> interfaces will no longer
    exist, unless you put such <quote>descriptive</quote> names in the NAME
    key). Use the descriptive names from the Udev rules instead
    of <quote>eth0</quote> in the network interface configuration files
    below.</para>

  </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>