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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>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, Udev comes with a script and some rules to assign stable names
to network cards based on their MAC address.</para>
<para>Pre-generate the rules to ensure the same names get assigned to the
same devices at every boot, including the first:</para>
<screen><userinput>/lib/udev/write_net_rules all_interfaces</userinput></screen>
<para>Now, inspect the <filename>/etc/udev/rules.d/70-persistent-net.rules</filename>
file, to find out which name was assigned to which network device:</para>
<screen><userinput>cat /etc/udev/rules.d/70-persistent-net.rules</userinput></screen>
<para>Each NIC takes up two lines in the file. The first line is a
description of the NIC itself, showing its hardware IDs (e.g. its PCI
vendor and device IDs, if it's a PCI card), along with its driver in
parentheses, if the driver can be found. This line is a comment; neither
the hardware ID nor the driver is used to determine which name to give an
interface. The second line is the Udev rule that matches this NIC and
actually assigns it a name.</para>
<para>All Udev rules are made up of several keys, separated by commas and
optional whitespace. This rule's keys and an explanations of each of them
are as follows:</para>
<itemizedlist>
<listitem>
<para><literal>SUBSYSTEM=="net"</literal> - This tells Udev to ignore
devices that are not network cards.</para>
</listitem>
<listitem>
<para><literal>DRIVERS=="?*"</literal> - This exists so that Udev will
ignore VLAN or bridge sub-interfaces (because these sub-interfaces do
not have drivers). These sub-interfaces are skipped because the name
that would be assigned would collide with their parent devices.</para>
</listitem>
<listitem>
<para><literal>ATTRS{type}=="1"</literal> - Optional. This key will
only be added if this NIC is a wireless NIC whose driver creates
multiple virtual interfaces; it ensures the rule only matches the
primary interface. The secondary interfaces are not matched for the
same reason that VLAN and bridge sub-interfaces are not matched: there
would be a name collision.</para>
</listitem>
<listitem>
<para><literal>ATTRS{address}</literal> - The value of this key is the
NIC's MAC address.</para>
</listitem>
<listitem>
<para><literal>NAME</literal> - The value of this key is the name that
Udev will assign to this interface.</para>
</listitem>
</itemizedlist>
<para>The value of <literal>NAME</literal> is the important part. Make sure
you know which name has been assigned to each of your network cards before
proceeding, and be sure to use that <literal>NAME</literal> value when
creating your 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 &&
mkdir -v ifconfig.eth0 &&
cat > ifconfig.eth0/ipv4 << "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 > /etc/resolv.conf << "EOF"
<literal># Begin /etc/resolv.conf
domain <replaceable><Your Domain Name></replaceable>
nameserver <replaceable><IP address of your primary nameserver></replaceable>
nameserver <replaceable><IP address of your secondary nameserver></replaceable>
# End /etc/resolv.conf</literal>
EOF</userinput></screen>
<para>Replace <replaceable><IP address of the nameserver></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>