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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<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 > /etc/udev/rules.d/26-network.rules << EOF
<literal>ACTION=="add", SUBSYSTEM=="net", SYSFS{address}=="<replaceable>00:e0:4c:12:34:56</replaceable>", \
NAME="<replaceable>realtek</replaceable>"
ACTION=="add", SUBSYSTEM=="net", SYSFS{address}=="<replaceable>00:a0:c9:78:9a:bc</replaceable>", \
NAME="<replaceable>intel</replaceable>"</literal>
EOF</userinput></screen>
<!-- 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. -->
<note>
<para>Although the examples in this book work properly, be aware that
<application>udev</application> does not recognize the backslash for line
continuation. If modifying <application>udev</application> rules with an
editor, be sure to leave each rule on one physical line.</para>
</note>
<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 > /etc/udev/rules.d/26-network.rules << 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>
<para>Note that the rules above don't work for every setup. For example,
MAC-based rules break when bridges or VLANs are used, because bridges and
VLANs have the same MAC address as the network card. One wants to rename
only the network card interface, not the bridge or VLAN interface, but the
example rule matches both. If you use such virtual interfaces, you have two
potential solutions. One is to add the DRIVER=="?*" key after
SUBSYSTEM=="net" in MAC-based rules which will stop matching the virtual
interfaces. This is known to fail with some older Ethernet cards because
they don't have the DRIVER variable in the uevent and thus the rule does
not match with such cards. Another solution is to switch to rules that use
the bus position as a key.</para>
<para>The second known non-working case is with wireless cards using the
MadWifi or HostAP drivers, because they create at least two interfaces with
the same MAC address and bus position. For example, the Madwifi driver
creates both an athX and a wifiX interface where X is a digit. To
differentiate these interfaces, add an appropriate KERNEL parameter such as
KERNEL=="ath*" after SUBSYSTEM=="net".</para>
<para>There may be other cases where the rules above don't work. Currently,
bugs on this topic are still being reported to Linux distributions, and no
solution that covers every case is available.</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>
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