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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<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>
<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>If there is only one network interface in the system to be
configured, this section is optional, although it will never be wrong to do
it. In many cases (e.g. a laptop with a wireless and a wired interface),
accomplishing the configuration in this section is necessary.</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, 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>for NIC in /sys/class/net/* ; do
INTERFACE=${NIC##*/} udevadm test --action=add $NIC
done</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 role="nodump"><userinput>cat /etc/udev/rules.d/70-persistent-net.rules</userinput></screen>
<para>The file begins with a comment block followed by two lines for each
NIC. The first line for each NIC is a commented description 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. Neither
the hardware ID nor the driver is used to determine which name to give an
interface; this information is only for reference. 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 explanation 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>ACTION=="add"</literal> - This tells Udev to ignore this
rule for a uevent that isn't an add ("remove" and "change" uevents also
happen, but don't need to rename network interfaces).</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>ATTR{address}</literal> - The value of this key is the
NIC's MAC address.</para>
</listitem>
<listitem>
<para><literal>ATTR{type}=="1"</literal> - This ensures the rule only
matches the primary interface in the case of certain wireless drivers,
which create multiple virtual interfaces. The secondary interfaces are
skipped for the same reason that VLAN and bridge sub-interfaces are
skipped: there would be a name collision otherwise.</para>
</listitem>
<listitem>
<para><literal>KERNEL=="eth*"</literal> - This key was added to the
Udev rule generator to handle machines that have multiple network
interfaces, all with the same MAC address (the PS3 is one such
machine). If the independent interfaces have different basenames,
this key will allow Udev to tell them apart. This is generally not
necessary for most Linux From Scratch users, but does not hurt.</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 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 > ifconfig.eth0 << "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 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>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><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>
<note><para>The Google Public IPv4 DNS addresses are 8.8.8.8 and 8.8.4.4.</para></note>
</sect2>
</sect1>
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