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>Network Interface Configuration Files</title>

    <para>Starting with version 209, systemd ships a network configuration
    daemon called <command>systemd-networkd</command> which can be used for
    basic network configuration. Additionally, since version 213, DNS name
    resolution can be handled by <command>systemd-resolved</command> in place
    of a static <filename>/etc/resolv.conf</filename> file. Both services are
    enabled by defualt, and absolutely should not be disabled.</para>

    <para>Configuration files for <command>systemd-networkd</command> (and
    <command>systemd-resolved</command>) can be placed in
    <filename class="directory">/usr/lib/systemd/network</filename>
    or <filename class="directory">/etc/systemd/network</filename>. Files in
    <filename class="directory">/etc/systemd/network</filename> have a
    higher priority than the ones in
    <filename class="directory">/usr/lib/systemd/network</filename>.
    There are three types of configuration files:
    <filename class="extension">.link</filename>,
    <filename class="extension">.netdev</filename> and
    <filename class="extension">.network</filename> files. For detailed
    descriptions and example contents of these configuration files, consult 
    the <filename>systemd-link(5)</filename>,
    <filename>systemd-netdev(5)</filename> and
    <filename>systemd-network(5)</filename> manual pages.</para>

    <note><para>Udev may assign network card interface names based
    on system physical characteristics such as enp2s1. If you are
    not sure what your interface name is, you can always run
    <command>ip link</command> after you have booted your system.
    </para></note>

    <sect3 id="systemd-networkd-static">
      <title>Static IP Configuration</title>

      <para>The command below creates a basic configuration file for a
      Static IP setup (using both systemd-networkd and
      systemd-resolved):</para>

<screen role="nodump"><userinput>cat &gt; /etc/systemd/network/10-eth0-static.network &lt;&lt; "EOF"
<literal>[Match]
Name=eth0

[Network]
Address=192.168.0.2/24
Gateway=192.168.0.1
DNS=192.168.0.1</literal>
EOF</userinput></screen>

      <para>Multiple DNS entries can be added if you have more than one DNS
      server.</para>

    </sect3>

    <sect3 id="systemd-networkd-dhcp">
      <title>DHCP Configuration</title>

      <para>The command below creates a basic configuration file for an IPv4
      DHCP setup:</para>

<screen role="nodump"><userinput>cat &gt; /etc/systemd/network/10-eth0-dhcp.network &lt;&lt; "EOF"
<literal>[Match]
Name=eth0

[Network]
DHCP=ipv4</literal>
EOF</userinput></screen>

    </sect3>

  </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>.</para>

    <sect3 id="resolv-conf-systemd-resoloved">
      <title>systemd-resolved Configuration</title>

      <note><para>If using another means to configure your network
      interfaces (ex: ppp, network-manager, etc.), or if using any type of
      local resolver (ex: bind, dnsmasq, etc.), or any other software that
      generates an <filename>/etc/resolv.conf</filename> (ex: resolvconf), the
      <command>systemd-resolved</command> service should not be
      used.</para></note>

      <para>When using <command>systemd-resolved</command> for DNS
      configuration, it is responsible for creating the
      <filename>/etc/resolv.conf</filename> file, which is placed in a
      non-standard location that is writable during early boot. In order to be
      used by other components of the system, it is necessary to create a
      symlink with the following command:</para>

<screen><userinput>ln -sfv /run/systemd/resolve/resolv.conf /etc/resolv.conf</userinput></screen>

      <para>This is required if you are specifying DNS entries in <filename
      class="extension">.network</filename> files or using the built in
      DHCP client to obtain DNS addresses.</para>

    </sect3>

    <sect3 id="resolv-conf-static">
      <title>Static resolv.conf Configuration</title>

      <para>If a static <filename>/etc/resolv.conf</filename> is desired,
      create it by running the following command:</para>

<screen role="nodump"><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
      <parameter>8.8.8.8</parameter> and <parameter>8.8.4.4</parameter>
      for IPv4, and <parameter>2001:4860:4860::8888</parameter> and
      <parameter>2001:4860:4860::8844</parameter> for IPv6.</para></note>

    </sect3>

  </sect2>

  <sect2 id="ch-scripts-hostname">
    <title>Configuring the system hostname</title>

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

     <para>During the boot process, the file <filename>/etc/hostname</filename>
     is used for establishing the system's hostname.</para>

     <para>Create the <filename>/etc/hostname</filename> file and enter a
     hostname by running:</para>

<screen><userinput>echo "<replaceable>&lt;lfs&gt;</replaceable>" &gt; /etc/hostname</userinput></screen>

     <para><replaceable>&lt;lfs&gt;</replaceable> needs to be replaced with the
     name given to the computer. Do not enter the Fully Qualified Domain Name
     (FQDN) here. That information is put in the
     <filename>/etc/hosts</filename> file.</para>

  </sect2>

  <sect2 id="ch-scripts-hosts">
     <title>Customizing the /etc/hosts File</title>

     <indexterm zone="ch-scripts-hosts">
       <primary sortas="e-/etc/hosts">/etc/hosts</primary>
     </indexterm>
   
     <indexterm zone="ch-scripts-hosts">
       <primary sortas="d-localnet">localnet</primary>
       <secondary>/etc/hosts</secondary>
     </indexterm>
   
     <indexterm zone="ch-scripts-hosts">
       <primary sortas="d-network">network</primary>
       <secondary>/etc/hosts</secondary>
     </indexterm>
   
     <para>Decide on the IP address, fully-qualified domain name (FQDN), and
     possible aliases for use in the <filename>/etc/hosts</filename> file. The
     syntax is:</para>
   
<screen><literal>IP_address myhost.example.org aliases</literal></screen>

     <para>Unless the computer is to be visible to the Internet (i.e., there is
     a registered domain and a valid block of assigned IP addresses&mdash;most
     users do not have this), make sure that the IP address is in the private
     network IP address range. Valid ranges are:</para>

<screen><literal>Private Network Address Range      Normal Prefix
10.0.0.1 - 10.255.255.254           8
172.x.0.1 - 172.x.255.254           16
192.168.y.1 - 192.168.y.254         24</literal></screen>

     <para>x can be any number in the range 16-31. y can be any number in the
     range 0-255.</para>
   
     <para>A valid private IP address could be 192.168.1.1. A valid FQDN for
     this IP could be lfs.example.org.</para>
   
     <para>Even if not using a network card, a valid FQDN is still required.
     This is necessary for certain programs to operate correctly.</para>
   
     <para>Create the  <filename>/etc/hosts</filename> file by running:</para>

<screen><userinput>cat &gt; /etc/hosts &lt;&lt; "EOF"
<literal># Begin /etc/hosts (network card version)

127.0.0.1 localhost
::1       localhost
<replaceable>&lt;192.168.0.2&gt;</replaceable> <replaceable>&lt;HOSTNAME.example.org&gt;</replaceable> <replaceable>[alias1] [alias2] ...</replaceable>

# End /etc/hosts (network card version)</literal>
EOF</userinput></screen>

     <para>The <replaceable>&lt;192.168.0.2&gt;</replaceable> and
     <replaceable>&lt;HOSTNAME.example.org&gt;</replaceable> values need to be
     changed for specific uses or requirements (if assigned an IP address by a
     network/system administrator and the machine will be connected to an
     existing network). The optional alias name(s) can be omitted.</para>
   
     <para>If a network card is not going to be configured, create the
     <filename>/etc/hosts</filename> file by running:</para>

<screen role="nodump"><userinput>cat &gt; /etc/hosts &lt;&lt; "EOF"
<literal># Begin /etc/hosts (no network card version)

127.0.0.1 <replaceable>&lt;HOSTNAME.example.org&gt;</replaceable> <replaceable>&lt;HOSTNAME&gt;</replaceable> localhost
::1       localhost

# End /etc/hosts (no network card version)</literal>
EOF</userinput></screen>

     <para>The ::1 entry is the IPv6 counterpart of 127.0.0.1 and represents the IPv6 loopback interface.</para>

   </sect2>

</sect1>