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<?xml version="1.0" encoding="iso-8859-2"?>
<!--
The FreeBSD Documentation Project
$FreeBSD$
-->
<chapter id="network-servers">
<chapterinfo>
<authorgroup>
<author>
<firstname>Murray</firstname>
<surname>Stokely</surname>
<contrib>Reorganized by </contrib>
</author>
</authorgroup>
<!-- 23 July 2004 -->
</chapterinfo>
<title>Network Servers</title>
<sect1 id="network-servers-synopsis">
<title>Synopsis</title>
<para>This chapter will cover some of the more frequently used
network services on &unix; systems. We will cover how to
install, configure, test, and maintain many different types of
network services. Example configuration files are included
throughout this chapter for you to benefit from.</para>
<para>After reading this chapter, you will know:</para>
<itemizedlist>
<listitem>
<para>How to manage the <application>inetd</application>
daemon.</para>
</listitem>
<listitem>
<para>How to set up a network file system.</para>
</listitem>
<listitem>
<para>How to set up a network information server for sharing
user accounts.</para>
</listitem>
<listitem>
<para>How to set up automatic network settings using DHCP.</para>
</listitem>
<listitem>
<para>How to set up a domain name server.</para>
</listitem>
<listitem>
<para>How to set up the <application>Apache</application> HTTP Server.</para>
</listitem>
<listitem>
<para>How to set up a File Transfer Protocol (FTP) Server.</para>
</listitem>
<listitem>
<para>How to set up a file and print server for &windows;
clients using <application>Samba</application>.</para>
</listitem>
<listitem>
<para>How to synchronize the time and date, and set up a
time server, with the NTP protocol.</para>
</listitem>
</itemizedlist>
<para>Before reading this chapter, you should:</para>
<itemizedlist>
<listitem>
<para>Understand the basics of the
<filename>/etc/rc</filename> scripts.</para>
</listitem>
<listitem>
<para>Be familiar with basic network terminology.</para>
</listitem>
<listitem>
<para>Know how to install additional third-party
software (<xref linkend="ports"/>).</para>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="network-inetd">
<sect1info>
<authorgroup>
<author>
<firstname>Chern</firstname>
<surname>Lee</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
<authorgroup>
<author>
<contrib>Updated for &os; 6.1-RELEASE by </contrib>
<othername>The &os; Documentation Project</othername>
</author>
</authorgroup>
</sect1info>
<title>The <application>inetd</application> <quote>Super-Server</quote></title>
<sect2 id="network-inetd-overview">
<title>Overview</title>
<para>&man.inetd.8; is sometimes referred to as the <quote>Internet
Super-Server</quote> because it manages connections for
several services. When a
connection is received by <application>inetd</application>, it
determines which program the connection is destined for, spawns
the particular process and delegates the socket to it (the program
is invoked with the service socket as its standard input, output
and error descriptors). Running
<application>inetd</application> for servers that are not heavily used can reduce the
overall system load, when compared to running each daemon
individually in stand-alone mode.</para>
<para>Primarily, <application>inetd</application> is used to
spawn other daemons, but several trivial protocols are handled
directly, such as <application>chargen</application>,
<application>auth</application>, and
<application>daytime</application>.</para>
<para>This section will cover the basics in configuring
<application>inetd</application> through its command-line
options and its configuration file,
<filename>/etc/inetd.conf</filename>.</para>
</sect2>
<sect2 id="network-inetd-settings">
<title>Settings</title>
<para><application>inetd</application> is initialized through
the &man.rc.8; system. The
<literal>inetd_enable</literal> option is set to
<literal>NO</literal> by default, but may be turned on
by <application>sysinstall</application> during installation,
depending on the configuration chosen by the user.
Placing:
<programlisting>inetd_enable="YES"</programlisting> or
<programlisting>inetd_enable="NO"</programlisting> into
<filename>/etc/rc.conf</filename> will enable or disable
<application>inetd</application> starting at boot time.
The command:
<programlisting>/etc/rc.d/inetd rcvar</programlisting>
can be run to display the current effective setting.</para>
<para>Additionally, different command-line options can be passed
to <application>inetd</application> via the
<literal>inetd_flags</literal> option.</para>
</sect2>
<sect2 id="network-inetd-cmdline">
<title>Command-Line Options</title>
<para>Like most server daemons, <application>inetd</application>
has a number of options that it can be passed in order to
modify its behaviour. The full list of options reads:</para>
<para><command>inetd</command> <option>[-d] [-l] [-w] [-W] [-c maximum] [-C rate] [-a address | hostname]
[-p filename] [-R rate] [-s maximum] [configuration file]</option></para>
<para>Options can be passed to <application>inetd</application> using the
<literal>inetd_flags</literal> option in
<filename>/etc/rc.conf</filename>. By default,
<literal>inetd_flags</literal> is set to
<literal>-wW -C 60</literal>, which turns on TCP wrapping for
<application>inetd</application>'s services, and prevents any
single IP address from requesting any service more than 60 times
in any given minute.</para>
<para>Novice users may be pleased to note that
these parameters usually do not need to be modified,
although we mention the rate-limiting options below as
they be useful should you find that you are receiving an
excessive amount of connections. A full list of options
can be found in the &man.inetd.8; manual.</para>
<variablelist>
<varlistentry>
<term>-c maximum</term>
<listitem>
<para>Specify the default maximum number of simultaneous
invocations of each service; the default is unlimited.
May be overridden on a per-service basis with the
<option>max-child</option> parameter.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-C rate</term>
<listitem>
<para>Specify the default maximum number of times a
service can be invoked from a single IP address in one
minute; the default is unlimited. May be overridden on a
per-service basis with the
<option>max-connections-per-ip-per-minute</option>
parameter.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-R rate</term>
<listitem>
<para>Specify the maximum number of times a service can be
invoked in one minute; the default is 256. A rate of 0
allows an unlimited number of invocations.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-s maximum</term>
<listitem>
<para>Specify the maximum number of times a service can be
invoked from a single IP address at any one time; the
default is unlimited. May be overridden on a per-service
basis with the <option>max-child-per-ip</option>
parameter.</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="network-inetd-conf">
<!-- XXX This section isn't very clear, and could do with some lovin' -->
<title><filename>inetd.conf</filename></title>
<para>Configuration of <application>inetd</application> is
done via the file <filename>/etc/inetd.conf</filename>.</para>
<para>When a modification is made to
<filename>/etc/inetd.conf</filename>,
<application>inetd</application> can be forced to re-read its
configuration file by running the command:</para>
<example id="network-inetd-reread">
<title>Reloading the <application>inetd</application>
configuration file</title>
<screen>&prompt.root; <userinput>/etc/rc.d/inetd reload</userinput></screen>
</example>
<para>Each line of the configuration file specifies an
individual daemon. Comments in the file are preceded by a
<quote>#</quote>. The format of each entry in
<filename>/etc/inetd.conf</filename> is as follows:</para>
<programlisting>service-name
socket-type
protocol
{wait|nowait}[/max-child[/max-connections-per-ip-per-minute[/max-child-per-ip]]]
user[:group][/login-class]
server-program
server-program-arguments</programlisting>
<para>An example entry for the &man.ftpd.8; daemon
using IPv4 might read:</para>
<programlisting>ftp stream tcp nowait root /usr/libexec/ftpd ftpd -l</programlisting>
<variablelist>
<varlistentry>
<term>service-name</term>
<listitem>
<para>This is the service name of the particular daemon.
It must correspond to a service listed in
<filename>/etc/services</filename>. This determines
which port <application>inetd</application> must listen
to. If a new service is being created, it must be
placed in <filename>/etc/services</filename>
first.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>socket-type</term>
<listitem>
<para>Either <literal>stream</literal>,
<literal>dgram</literal>, <literal>raw</literal>, or
<literal>seqpacket</literal>. <literal>stream</literal>
must be used for connection-based, TCP daemons, while
<literal>dgram</literal> is used for daemons utilizing
the <acronym>UDP</acronym> transport protocol.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>protocol</term>
<listitem>
<para>One of the following:</para>
<informaltable frame="none" pgwide="1">
<tgroup cols="2">
<thead>
<row>
<entry>Protocol</entry>
<entry>Explanation</entry>
</row>
</thead>
<tbody>
<row>
<entry>tcp, tcp4</entry>
<entry>TCP IPv4</entry>
</row>
<row>
<entry>udp, udp4</entry>
<entry>UDP IPv4</entry>
</row>
<row>
<entry>tcp6</entry>
<entry>TCP IPv6</entry>
</row>
<row>
<entry>udp6</entry>
<entry>UDP IPv6</entry>
</row>
<row>
<entry>tcp46</entry>
<entry>Both TCP IPv4 and v6</entry>
</row>
<row>
<entry>udp46</entry>
<entry>Both UDP IPv4 and v6</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
</varlistentry>
<varlistentry>
<term>{wait|nowait}[/max-child[/max-connections-per-ip-per-minute[/max-child-per-ip]]]</term>
<listitem>
<para><option>wait|nowait</option> indicates whether the
daemon invoked from <application>inetd</application> is
able to handle its own socket or not.
<option>dgram</option> socket types must use the
<option>wait</option> option, while stream socket
daemons, which are usually multi-threaded, should use
<option>nowait</option>. <option>wait</option> usually
hands off multiple sockets to a single daemon, while
<option>nowait</option> spawns a child daemon for each
new socket.</para>
<para>The maximum number of child daemons
<application>inetd</application> may spawn can be set
using the <option>max-child</option> option. If a limit
of ten instances of a particular daemon is needed, a
<literal>/10</literal> would be placed after
<option>nowait</option>. Specifying <literal>/0</literal>
allows an unlimited number of children</para>
<para>In addition to <option>max-child</option>, two other
options which limit the maximum connections from a single
place to a particular daemon can be enabled.
<option>max-connections-per-ip-per-minute</option> limits
the number of connections from any particular IP address
per minutes, e.g. a value of ten would limit any particular
IP address connecting to a particular service to ten
attempts per minute. <option>max-child-per-ip</option>
limits the number of children that can be started on
behalf on any single IP address at any moment. These
options are useful to prevent intentional or unintentional
excessive resource consumption and Denial of Service (DoS)
attacks to a machine.</para>
<para>In this field, either of <option>wait</option> or
<option>nowait</option> is mandatory.
<option>max-child</option>,
<option>max-connections-per-ip-per-minute</option> and
<option>max-child-per-ip</option> are
optional.</para>
<para>A stream-type multi-threaded daemon without any
<option>max-child</option>,
<option>max-connections-per-ip-per-minute</option> or
<option>max-child-per-ip</option> limits
would simply be: <literal>nowait</literal>.</para>
<para>The same daemon with a maximum limit of ten daemons
would read: <literal>nowait/10</literal>.</para>
<para>The same setup with a limit of twenty
connections per IP address per minute and a maximum
total limit of ten child daemons would read:
<literal>nowait/10/20</literal>.</para>
<para>These options are utilized by the default
settings of the &man.fingerd.8; daemon,
as seen here:</para>
<programlisting>finger stream tcp nowait/3/10 nobody /usr/libexec/fingerd fingerd -s</programlisting>
<para>Finally, an example of this field with a maximum of
100 children in total, with a maximum of 5 for any one
IP address would read:
<literal>nowait/100/0/5</literal>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>user</term>
<listitem>
<para>This is the username that the particular daemon
should run as. Most commonly, daemons run as the
<username>root</username> user. For security purposes, it is
common to find some servers running as the
<username>daemon</username> user, or the least privileged
<username>nobody</username> user.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>server-program</term>
<listitem>
<para>The full path of the daemon to be executed when a
connection is received. If the daemon is a service
provided by <application>inetd</application> internally,
then <option>internal</option> should be
used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>server-program-arguments</term>
<listitem>
<para>This works in conjunction with
<option>server-program</option> by specifying the
arguments, starting with <literal>argv[0]</literal>,
passed to the daemon on invocation. If
<command>mydaemon -d</command> is the command line,
<literal>mydaemon -d</literal> would be the value of
<option>server-program-arguments</option>. Again, if
the daemon is an internal service, use
<option>internal</option> here.</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="network-inetd-security">
<title>Security</title>
<para>Depending on the choices made at install time, many
of <application>inetd</application>'s services may be enabled
by default. If there is no apparent need for a particular
daemon, consider disabling it. Place a <quote>#</quote> in front of the
daemon in question in <filename>/etc/inetd.conf</filename>,
and then <link linkend="network-inetd-reread">reload the
inetd configuration</link>. Some daemons, such as
<application>fingerd</application>, may not be desired at all
because they provide
information that may be useful to an attacker.</para>
<para>Some daemons are not security-conscious and have long, or
non-existent, timeouts for connection attempts. This allows an
attacker to slowly send connections to a particular daemon,
thus saturating available resources. It may be a good idea to
place <option>max-connections-per-ip-per-minute</option>,
<option>max-child</option> or <option>max-child-per-ip</option> limitations on certain
daemons if you find that you have too many connections.</para>
<para>By default, TCP wrapping is turned on. Consult the
&man.hosts.access.5; manual page for more information on placing
TCP restrictions on various <application>inetd</application>
invoked daemons.</para>
</sect2>
<sect2 id="network-inetd-misc">
<title>Miscellaneous</title>
<para><application>daytime</application>,
<application>time</application>,
<application>echo</application>,
<application>discard</application>,
<application>chargen</application>, and
<application>auth</application> are all internally provided
services of <application>inetd</application>.</para>
<para>The <application>auth</application> service provides
identity
network services, and is
configurable to a certain degree, whilst the others are simply on or off.</para>
<para>Consult the &man.inetd.8; manual page for more in-depth
information.</para>
</sect2>
</sect1>
<sect1 id="network-nfs">
<sect1info>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Rhodes</surname>
<contrib>Reorganized and enhanced by </contrib>
</author>
</authorgroup>
<authorgroup>
<author>
<firstname>Bill</firstname>
<surname>Swingle</surname>
<contrib>Written by </contrib>
</author>
</authorgroup>
</sect1info>
<title>Network File System (NFS)</title>
<indexterm><primary>NFS</primary></indexterm>
<para>Among the many different file systems that FreeBSD supports
is the Network File System, also known as <acronym role="Network
File System">NFS</acronym>. <acronym role="Network File
System">NFS</acronym> allows a system to share directories and
files with others over a network. By using <acronym
role="Network File System">NFS</acronym>, users and programs can
access files on remote systems almost as if they were local
files.</para>
<para>Some of the most notable benefits that
<acronym>NFS</acronym> can provide are:</para>
<itemizedlist>
<listitem>
<para>Local workstations use less disk space because commonly
used data can be stored on a single machine and still remain
accessible to others over the network.</para>
</listitem>
<listitem>
<para>There is no need for users to have separate home
directories on every network machine. Home directories
could be set up on the <acronym>NFS</acronym> server and
made available throughout the network.</para>
</listitem>
<listitem>
<para>Storage devices such as floppy disks, CDROM drives, and
&iomegazip; drives can be used by other machines on the network.
This may reduce the number of removable media drives
throughout the network.</para>
</listitem>
</itemizedlist>
<sect2>
<title>How <acronym>NFS</acronym> Works</title>
<para><acronym>NFS</acronym> consists of at least two main
parts: a server and one or more clients. The client remotely
accesses the data that is stored on the server machine. In
order for this to function properly a few processes have to be
configured and running.</para>
<para>The server has to be running the following daemons:</para>
<indexterm>
<primary>NFS</primary>
<secondary>server</secondary>
</indexterm>
<indexterm>
<primary>file server</primary>
<secondary>UNIX clients</secondary>
</indexterm>
<indexterm>
<primary><application>rpcbind</application></primary>
</indexterm>
<indexterm>
<primary><application>mountd</application></primary>
</indexterm>
<indexterm>
<primary><application>nfsd</application></primary>
</indexterm>
<informaltable frame="none" pgwide="1">
<tgroup cols="2">
<colspec colwidth="1*"/>
<colspec colwidth="3*"/>
<thead>
<row>
<entry>Daemon</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><application>nfsd</application></entry>
<entry>The <acronym>NFS</acronym> daemon which services
requests from the <acronym>NFS</acronym>
clients.</entry>
</row>
<row>
<entry><application>mountd</application></entry>
<entry>The <acronym>NFS</acronym> mount daemon which carries out
the requests that &man.nfsd.8; passes on to it.</entry>
</row>
<row>
<entry><application>rpcbind</application></entry>
<entry> This daemon allows
<acronym>NFS</acronym> clients to discover which port
the <acronym>NFS</acronym> server is using.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>The client can also run a daemon, known as
<application>nfsiod</application>. The
<application>nfsiod</application> daemon services the requests
from the <acronym>NFS</acronym> server. This is optional, and
improves performance, but is not required for normal and
correct operation. See the &man.nfsiod.8; manual page for
more information.
</para>
</sect2>
<sect2 id="network-configuring-nfs">
<title>Configuring <acronym>NFS</acronym></title>
<indexterm>
<primary>NFS</primary>
<secondary>configuration</secondary>
</indexterm>
<para><acronym>NFS</acronym> configuration is a relatively
straightforward process. The processes that need to be
running can all start at boot time with a few modifications to
your <filename>/etc/rc.conf</filename> file.</para>
<para>On the <acronym>NFS</acronym> server, make sure that the
following options are configured in the
<filename>/etc/rc.conf</filename> file:</para>
<programlisting>rpcbind_enable="YES"
nfs_server_enable="YES"
mountd_flags="-r"</programlisting>
<para><application>mountd</application> runs automatically
whenever the <acronym>NFS</acronym> server is enabled.</para>
<para>On the client, make sure this option is present in
<filename>/etc/rc.conf</filename>:</para>
<programlisting>nfs_client_enable="YES"</programlisting>
<para>The <filename>/etc/exports</filename> file specifies which
file systems <acronym>NFS</acronym> should export (sometimes
referred to as <quote>share</quote>). Each line in
<filename>/etc/exports</filename> specifies a file system to be
exported and which machines have access to that file system.
Along with what machines have access to that file system,
access options may also be specified. There are many such
options that can be used in this file but only a few will be
mentioned here. You can easily discover other options by
reading over the &man.exports.5; manual page.</para>
<para>Here are a few example <filename>/etc/exports</filename>
entries:</para>
<indexterm>
<primary>NFS</primary>
<secondary>export examples</secondary>
</indexterm>
<para>The following examples give an idea of how to export
file systems, although the settings may be different depending
on your environment and network configuration. For instance,
to export the <filename>/cdrom</filename> directory to three
example machines that have the same domain name as the server
(hence the lack of a domain name for each) or have entries in
your <filename>/etc/hosts</filename> file. The
<option>-ro</option> flag makes the exported file system
read-only. With this flag, the remote system will not be able
to write any changes to the exported file system.</para>
<programlisting>/cdrom -ro host1 host2 host3</programlisting>
<para>The following line exports <filename>/home</filename> to
three hosts by IP address. This is a useful setup if you have
a private network without a <acronym>DNS</acronym> server
configured. Optionally the <filename>/etc/hosts</filename>
file could be configured for internal hostnames; please review
&man.hosts.5; for more information. The
<option>-alldirs</option> flag allows the subdirectories to be
mount points. In other words, it will not mount the
subdirectories but permit the client to mount only the
directories that are required or needed.</para>
<programlisting>/home -alldirs 10.0.0.2 10.0.0.3 10.0.0.4</programlisting>
<para>The following line exports <filename>/a</filename> so that
two clients from different domains may access the file system.
The <option>-maproot=root</option> flag allows the
<username>root</username> user on the remote system to write
data on the exported file system as <username>root</username>.
If the <literal>-maproot=root</literal> flag is not specified,
then even if a user has <username>root</username> access on
the remote system, he will not be able to modify files on
the exported file system.</para>
<programlisting>/a -maproot=root host.example.com box.example.org</programlisting>
<para>In order for a client to access an exported file system,
the client must have permission to do so. Make sure the
client is listed in your <filename>/etc/exports</filename>
file.</para>
<para>In <filename>/etc/exports</filename>, each line represents
the export information for one file system to one host. A
remote host can only be specified once per file system, and may
only have one default entry. For example, assume that
<filename>/usr</filename> is a single file system. The
following <filename>/etc/exports</filename> would be
invalid:</para>
<programlisting># Invalid when /usr is one file system
/usr/src client
/usr/ports client</programlisting>
<para>One file system, <filename>/usr</filename>, has two lines
specifying exports to the same host, <hostid>client</hostid>.
The correct format for this situation is:</para>
<programlisting>/usr/src /usr/ports client</programlisting>
<para>The properties of one file system exported to a given host
must all occur on one line. Lines without a client specified
are treated as a single host. This limits how you can export
file systems, but for most people this is not an issue.</para>
<para>The following is an example of a valid export list, where
<filename>/usr</filename> and <filename>/exports</filename>
are local file systems:</para>
<programlisting># Export src and ports to client01 and client02, but only
# client01 has root privileges on it
/usr/src /usr/ports -maproot=root client01
/usr/src /usr/ports client02
# The client machines have root and can mount anywhere
# on /exports. Anyone in the world can mount /exports/obj read-only
/exports -alldirs -maproot=root client01 client02
/exports/obj -ro</programlisting>
<para>The <application>mountd</application> daemon must be forced to
recheck the <filename>/etc/exports</filename> file whenever it has
been modified, so the changes can take effect. This can be
accomplished either by sending a HUP signal to the running daemon:</para>
<screen>&prompt.root; <userinput>kill -HUP `cat /var/run/mountd.pid`</userinput></screen>
<para>or by invoking the <command>mountd</command> &man.rc.8; script
with the appropriate parameter:</para>
<screen>&prompt.root; <userinput>/etc/rc.d/mountd reload</userinput></screen>
<para>Please refer to <xref linkend="configtuning-rcd"/> for more
information about using rc scripts.</para>
<para>Alternatively, a reboot will make FreeBSD set everything
up properly. A reboot is not necessary though.
Executing the following commands as <username>root</username>
should start everything up.</para>
<para>On the <acronym>NFS</acronym> server:</para>
<screen>&prompt.root; <userinput>rpcbind</userinput>
&prompt.root; <userinput>nfsd -u -t -n 4</userinput>
&prompt.root; <userinput>mountd -r</userinput></screen>
<para>On the <acronym>NFS</acronym> client:</para>
<screen>&prompt.root; <userinput>nfsiod -n 4</userinput></screen>
<para>Now everything should be ready to actually mount a remote file
system. In these examples the
server's name will be <hostid>server</hostid> and the client's
name will be <hostid>client</hostid>. If you only want to
temporarily mount a remote file system or would rather test the
configuration, just execute a command like this as <username>root</username> on the
client:</para>
<indexterm>
<primary>NFS</primary>
<secondary>mounting</secondary>
</indexterm>
<screen>&prompt.root; <userinput>mount server:/home /mnt</userinput></screen>
<para>This will mount the <filename>/home</filename> directory
on the server at <filename>/mnt</filename> on the client. If
everything is set up correctly you should be able to enter
<filename>/mnt</filename> on the client and see all the files
that are on the server.</para>
<para>If you want to automatically mount a remote file system
each time the computer boots, add the file system to the
<filename>/etc/fstab</filename> file. Here is an example:</para>
<programlisting>server:/home /mnt nfs rw 0 0</programlisting>
<para>The &man.fstab.5; manual page lists all the available
options.</para>
</sect2>
<sect2>
<title>Practical Uses</title>
<para><acronym>NFS</acronym> has many practical uses. Some of
the more common ones are listed below:</para>
<indexterm>
<primary>NFS</primary>
<secondary>uses</secondary>
</indexterm>
<itemizedlist>
<listitem>
<para>Set several machines to share a CDROM or other media
among them. This is cheaper and often a more convenient
method to install software on multiple machines.</para>
</listitem>
<listitem>
<para>On large networks, it might be more convenient to
configure a central <acronym>NFS</acronym> server in which
to store all the user home directories. These home
directories can then be exported to the network so that
users would always have the same home directory,
regardless of which workstation they log in to.</para>
</listitem>
<listitem>
<para>Several machines could have a common
<filename>/usr/ports/distfiles</filename> directory. That
way, when you need to install a port on several machines,
you can quickly access the source without downloading it
on each machine.</para>
</listitem>
</itemizedlist>
</sect2>
<sect2 id="network-amd">
<sect2info>
<authorgroup>
<author>
<firstname>Wylie</firstname>
<surname>Stilwell</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
<authorgroup>
<author>
<firstname>Chern</firstname>
<surname>Lee</surname>
<contrib>Rewritten by </contrib>
</author>
</authorgroup>
</sect2info>
<title>Automatic Mounts with <application>amd</application></title>
<indexterm><primary>amd</primary></indexterm>
<indexterm><primary>automatic mounter daemon</primary></indexterm>
<para>&man.amd.8; (the automatic mounter daemon)
automatically mounts a
remote file system whenever a file or directory within that
file system is accessed. Filesystems that are inactive for a
period of time will also be automatically unmounted by
<application>amd</application>. Using
<application>amd</application> provides a simple alternative
to permanent mounts, as permanent mounts are usually listed in
<filename>/etc/fstab</filename>.</para>
<para><application>amd</application> operates by attaching
itself as an NFS server to the <filename>/host</filename> and
<filename>/net</filename> directories. When a file is accessed
within one of these directories, <application>amd</application>
looks up the corresponding remote mount and automatically mounts
it. <filename>/net</filename> is used to mount an exported
file system from an IP address, while <filename>/host</filename>
is used to mount an export from a remote hostname.</para>
<para>An access to a file within
<filename>/host/foobar/usr</filename> would tell
<application>amd</application> to attempt to mount the
<filename>/usr</filename> export on the host
<hostid>foobar</hostid>.</para>
<example>
<title>Mounting an Export with <application>amd</application></title>
<para>You can view the available mounts of a remote host with
the <command>showmount</command> command. For example, to
view the mounts of a host named <hostid>foobar</hostid>, you
can use:</para>
<screen>&prompt.user; <userinput>showmount -e foobar</userinput>
Exports list on foobar:
/usr 10.10.10.0
/a 10.10.10.0
&prompt.user; <userinput>cd /host/foobar/usr</userinput></screen>
</example>
<para>As seen in the example, the <command>showmount</command> shows
<filename>/usr</filename> as an export. When changing directories to
<filename>/host/foobar/usr</filename>, <application>amd</application>
attempts to resolve the hostname <hostid>foobar</hostid> and
automatically mount the desired export.</para>
<para><application>amd</application> can be started by the
startup scripts by placing the following lines in
<filename>/etc/rc.conf</filename>:</para>
<programlisting>amd_enable="YES"</programlisting>
<para>Additionally, custom flags can be passed to
<application>amd</application> from the
<varname>amd_flags</varname> option. By default,
<varname>amd_flags</varname> is set to:</para>
<programlisting>amd_flags="-a /.amd_mnt -l syslog /host /etc/amd.map /net /etc/amd.map"</programlisting>
<para>The <filename>/etc/amd.map</filename> file defines the
default options that exports are mounted with. The
<filename>/etc/amd.conf</filename> file defines some of the more
advanced features of <application>amd</application>.</para>
<para>Consult the &man.amd.8; and &man.amd.conf.5; manual pages for more
information.</para>
</sect2>
<sect2 id="network-nfs-integration">
<sect2info>
<authorgroup>
<author>
<firstname>John</firstname>
<surname>Lind</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</sect2info>
<title>Problems Integrating with Other Systems</title>
<para>Certain Ethernet adapters for ISA PC systems have limitations
which can lead to serious network problems, particularly with NFS.
This difficulty is not specific to FreeBSD, but FreeBSD systems
are affected by it.</para>
<para>The problem nearly always occurs when (FreeBSD) PC systems are
networked with high-performance workstations, such as those made
by Silicon Graphics, Inc., and Sun Microsystems, Inc. The NFS
mount will work fine, and some operations may succeed, but
suddenly the server will seem to become unresponsive to the
client, even though requests to and from other systems continue to
be processed. This happens to the client system, whether the
client is the FreeBSD system or the workstation. On many systems,
there is no way to shut down the client gracefully once this
problem has manifested itself. The only solution is often to
reset the client, because the NFS situation cannot be
resolved.</para>
<para>Though the <quote>correct</quote> solution is to get a
higher performance and capacity Ethernet adapter for the
FreeBSD system, there is a simple workaround that will allow
satisfactory operation. If the FreeBSD system is the
<emphasis>server</emphasis>, include the option
<option>-w=1024</option> on the mount from the client. If the
FreeBSD system is the <emphasis>client</emphasis>, then mount
the NFS file system with the option <option>-r=1024</option>.
These options may be specified using the fourth field of the
<filename>fstab</filename> entry on the client for automatic
mounts, or by using the <option>-o</option> parameter of the
&man.mount.8; command for manual mounts.</para>
<para>It should be noted that there is a different problem,
sometimes mistaken for this one, when the NFS servers and
clients are on different networks. If that is the case, make
<emphasis>certain</emphasis> that your routers are routing the
necessary <acronym>UDP</acronym> information, or you will not get anywhere, no
matter what else you are doing.</para>
<para>In the following examples, <hostid>fastws</hostid> is the host
(interface) name of a high-performance workstation, and
<hostid>freebox</hostid> is the host (interface) name of a FreeBSD
system with a lower-performance Ethernet adapter. Also,
<filename>/sharedfs</filename> will be the exported NFS
file system (see &man.exports.5;), and
<filename>/project</filename> will be the mount point on the
client for the exported file system. In all cases, note that
additional options, such as <option>hard</option> or
<option>soft</option> and <option>bg</option> may be desirable in
your application.</para>
<para>Examples for the FreeBSD system (<hostid>freebox</hostid>)
as the client in <filename>/etc/fstab</filename> on
<hostid>freebox</hostid>:</para>
<programlisting>fastws:/sharedfs /project nfs rw,-r=1024 0 0</programlisting>
<para>As a manual mount command on <hostid>freebox</hostid>:</para>
<screen>&prompt.root; <userinput>mount -t nfs -o -r=1024 fastws:/sharedfs /project</userinput></screen>
<para>Examples for the FreeBSD system as the server in
<filename>/etc/fstab</filename> on
<hostid>fastws</hostid>:</para>
<programlisting>freebox:/sharedfs /project nfs rw,-w=1024 0 0</programlisting>
<para>As a manual mount command on <hostid>fastws</hostid>:</para>
<screen>&prompt.root; <userinput>mount -t nfs -o -w=1024 freebox:/sharedfs /project</userinput></screen>
<para>Nearly any 16-bit Ethernet adapter will allow operation
without the above restrictions on the read or write size.</para>
<para>For anyone who cares, here is what happens when the
failure occurs, which also explains why it is unrecoverable.
NFS typically works with a <quote>block</quote> size of
8&nbsp;K (though it may do fragments of smaller sizes). Since
the maximum Ethernet packet is around 1500&nbsp;bytes, the NFS
<quote>block</quote> gets split into multiple Ethernet
packets, even though it is still a single unit to the
upper-level code, and must be received, assembled, and
<emphasis>acknowledged</emphasis> as a unit. The
high-performance workstations can pump out the packets which
comprise the NFS unit one right after the other, just as close
together as the standard allows. On the smaller, lower
capacity cards, the later packets overrun the earlier packets
of the same unit before they can be transferred to the host
and the unit as a whole cannot be reconstructed or
acknowledged. As a result, the workstation will time out and
try again, but it will try again with the entire 8&nbsp;K
unit, and the process will be repeated, ad infinitum.</para>
<para>By keeping the unit size below the Ethernet packet size
limitation, we ensure that any complete Ethernet packet
received can be acknowledged individually, avoiding the
deadlock situation.</para>
<para>Overruns may still occur when a high-performance
workstations is slamming data out to a PC system, but with the
better cards, such overruns are not guaranteed on NFS
<quote>units</quote>. When an overrun occurs, the units
affected will be retransmitted, and there will be a fair
chance that they will be received, assembled, and
acknowledged.</para>
</sect2>
</sect1>
<sect1 id="network-nis">
<sect1info>
<authorgroup>
<author>
<firstname>Bill</firstname>
<surname>Swingle</surname>
<contrib>Written by </contrib>
</author>
</authorgroup>
<authorgroup>
<author>
<firstname>Eric</firstname>
<surname>Ogren</surname>
<contrib>Enhanced by </contrib>
</author>
<author>
<firstname>Udo</firstname>
<surname>Erdelhoff</surname>
</author>
</authorgroup>
</sect1info>
<title>Network Information System (NIS/YP)</title>
<sect2>
<title>What Is It?</title>
<indexterm><primary>NIS</primary></indexterm>
<indexterm><primary>Solaris</primary></indexterm>
<indexterm><primary>HP-UX</primary></indexterm>
<indexterm><primary>AIX</primary></indexterm>
<indexterm><primary>Linux</primary></indexterm>
<indexterm><primary>NetBSD</primary></indexterm>
<indexterm><primary>OpenBSD</primary></indexterm>
<para><acronym role="Network Information System">NIS</acronym>,
which stands for Network Information Services, was developed
by Sun Microsystems to centralize administration of &unix;
(originally &sunos;) systems. It has now essentially become
an industry standard; all major &unix; like systems
(&solaris;, HP-UX, &aix;, Linux, NetBSD, OpenBSD, FreeBSD,
etc) support <acronym role="Network Information
System">NIS</acronym>.</para>
<indexterm><primary>yellow pages</primary><see>NIS</see></indexterm>
<para><acronym role="Network Information System">NIS</acronym>
was formerly known as Yellow Pages, but because of trademark
issues, Sun changed the name. The old term (and yp) is still
often seen and used.</para>
<indexterm>
<primary>NIS</primary>
<secondary>domains</secondary>
</indexterm>
<para>It is a RPC-based client/server system that allows a group
of machines within an NIS domain to share a common set of
configuration files. This permits a system administrator to
set up NIS client systems with only minimal configuration data
and add, remove or modify configuration data from a single
location.</para>
<indexterm><primary>Windows NT</primary></indexterm>
<para>It is similar to the &windowsnt; domain system; although
the internal implementation of the two are not at all similar,
the basic functionality can be compared.</para>
</sect2>
<sect2>
<title>Terms/Processes You Should Know</title>
<para>There are several terms and several important user
processes that you will come across when attempting to
implement NIS on FreeBSD, whether you are trying to create an
NIS server or act as an NIS client:</para>
<indexterm>
<primary><application>rpcbind</application></primary>
</indexterm>
<indexterm>
<primary><application>portmap</application></primary>
</indexterm>
<informaltable frame="none" pgwide="1">
<tgroup cols="2">
<colspec colwidth="1*"/>
<colspec colwidth="3*"/>
<thead>
<row>
<entry>Term</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>NIS domainname</entry>
<entry>An NIS master server and all of its clients
(including its slave servers) have a NIS domainname.
Similar to an &windowsnt; domain name, the NIS
domainname does not have anything to do with
<acronym>DNS</acronym>.</entry>
</row>
<row>
<entry><application>rpcbind</application></entry>
<entry>Must be running in order to enable
<acronym>RPC</acronym> (Remote Procedure Call, a
network protocol used by NIS). If
<application>rpcbind</application> is not running, it
will be impossible to run an NIS server, or to act as
an NIS client.</entry>
</row>
<row>
<entry><application>ypbind</application></entry>
<entry><quote>Binds</quote> an NIS client to its NIS
server. It will take the NIS domainname from the
system, and using <acronym>RPC</acronym>, connect to
the server. <application>ypbind</application> is the
core of client-server communication in an NIS
environment; if <application>ypbind</application> dies
on a client machine, it will not be able to access the
NIS server.</entry>
</row>
<row>
<entry><application>ypserv</application></entry>
<entry>Should only be running on NIS servers; this is
the NIS server process itself. If &man.ypserv.8;
dies, then the server will no longer be able to
respond to NIS requests (hopefully, there is a slave
server to take over for it). There are some
implementations of NIS (but not the FreeBSD one), that
do not try to reconnect to another server if the
server it used before dies. Often, the only thing
that helps in this case is to restart the server
process (or even the whole server) or the
<application>ypbind</application> process on the
client.
</entry>
</row>
<row>
<entry><application>rpc.yppasswdd</application></entry>
<entry>Another process that should only be running on
NIS master servers; this is a daemon that will allow NIS
clients to change their NIS passwords. If this daemon
is not running, users will have to login to the NIS
master server and change their passwords there.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<!-- XXX Missing: rpc.ypxfrd (not important, though) May only run
on the master -->
</sect2>
<sect2>
<title>How Does It Work?</title>
<para>There are three types of hosts in an NIS environment:
master servers, slave servers, and clients. Servers act as a
central repository for host configuration information. Master
servers hold the authoritative copy of this information, while
slave servers mirror this information for redundancy. Clients
rely on the servers to provide this information to
them.</para>
<para>Information in many files can be shared in this manner.
The <filename>master.passwd</filename>,
<filename>group</filename>, and <filename>hosts</filename>
files are commonly shared via NIS. Whenever a process on a
client needs information that would normally be found in these
files locally, it makes a query to the NIS server that it is
bound to instead.</para>
<sect3>
<title>Machine Types</title>
<itemizedlist>
<indexterm>
<primary>NIS</primary>
<secondary>master server</secondary>
</indexterm>
<listitem>
<para>A <emphasis>NIS master server</emphasis>. This
server, analogous to a &windowsnt; primary domain
controller, maintains the files used by all of the NIS
clients. The <filename>passwd</filename>,
<filename>group</filename>, and other various files used
by the NIS clients live on the master server.</para>
<note><para>It is possible for one machine to be an NIS
master server for more than one NIS domain. However,
this will not be covered in this introduction, which
assumes a relatively small-scale NIS
environment.</para></note>
</listitem>
<listitem>
<indexterm>
<primary>NIS</primary>
<secondary>slave server</secondary>
</indexterm>
<para><emphasis>NIS slave servers</emphasis>. Similar to
the &windowsnt; backup domain controllers, NIS slave
servers maintain copies of the NIS master's data files.
NIS slave servers provide the redundancy, which is
needed in important environments. They also help to
balance the load of the master server: NIS Clients
always attach to the NIS server whose response they get
first, and this includes slave-server-replies.</para>
</listitem>
<listitem>
<indexterm>
<primary>NIS</primary>
<secondary>client</secondary>
</indexterm>
<para><emphasis>NIS clients</emphasis>. NIS clients, like
most &windowsnt; workstations, authenticate against the
NIS server (or the &windowsnt; domain controller in the
&windowsnt; workstations case) to log on.</para>
</listitem>
</itemizedlist>
</sect3>
</sect2>
<sect2>
<title>Using NIS/YP</title>
<para>This section will deal with setting up a sample NIS
environment.</para>
<note><para>This section assumes that you are running
FreeBSD&nbsp;3.3 or later. The instructions given here will
<emphasis>probably</emphasis> work for any version of FreeBSD
greater than 3.0, but there are no guarantees that this is
true.</para></note>
<sect3>
<title>Planning</title>
<para>Let us assume that you are the administrator of a small
university lab. This lab, which consists of 15 FreeBSD
machines, currently has no centralized point of
administration; each machine has its own
<filename>/etc/passwd</filename> and
<filename>/etc/master.passwd</filename>. These files are
kept in sync with each other only through manual
intervention; currently, when you add a user to the lab, you
must run <command>adduser</command> on all 15 machines.
Clearly, this has to change, so you have decided to convert
the lab to use NIS, using two of the machines as
servers.</para>
<para>Therefore, the configuration of the lab now looks something
like:</para>
<informaltable frame="none" pgwide="1">
<tgroup cols="3">
<thead>
<row>
<entry>Machine name</entry>
<entry>IP address</entry>
<entry>Machine role</entry>
</row>
</thead>
<tbody>
<row>
<entry><hostid>ellington</hostid></entry>
<entry><hostid role="ipaddr">10.0.0.2</hostid></entry>
<entry>NIS master</entry>
</row>
<row>
<entry><hostid>coltrane</hostid></entry>
<entry><hostid role="ipaddr">10.0.0.3</hostid></entry>
<entry>NIS slave</entry>
</row>
<row>
<entry><hostid>basie</hostid></entry>
<entry><hostid role="ipaddr">10.0.0.4</hostid></entry>
<entry>Faculty workstation</entry>
</row>
<row>
<entry><hostid>bird</hostid></entry>
<entry><hostid role="ipaddr">10.0.0.5</hostid></entry>
<entry>Client machine</entry>
</row>
<row>
<entry><hostid>cli[1-11]</hostid></entry>
<entry><hostid role="ipaddr">10.0.0.[6-17]</hostid></entry>
<entry>Other client machines</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>If you are setting up a NIS scheme for the first time, it
is a good idea to think through how you want to go about it. No
matter what the size of your network, there are a few decisions
that need to be made.</para>
<sect4>
<title>Choosing a NIS Domain Name</title>
<indexterm>
<primary>NIS</primary>
<secondary>domainname</secondary>
</indexterm>
<para>This might not be the <quote>domainname</quote> that
you are used to. It is more accurately called the
<quote>NIS domainname</quote>. When a client broadcasts
its requests for info, it includes the name of the NIS
domain that it is part of. This is how multiple servers
on one network can tell which server should answer which
request. Think of the NIS domainname as the name for a
group of hosts that are related in some way.</para>
<para>Some organizations choose to use their Internet
domainname for their NIS domainname. This is not
recommended as it can cause confusion when trying to debug
network problems. The NIS domainname should be unique
within your network and it is helpful if it describes the
group of machines it represents. For example, the Art
department at Acme Inc. might be in the
<quote>acme-art</quote> NIS domain. For this example,
assume you have chosen the name
<literal>test-domain</literal>.</para>
<indexterm><primary>SunOS</primary></indexterm>
<para>However, some operating systems (notably &sunos;) use
their NIS domain name as their Internet domain name. If one
or more machines on your network have this restriction, you
<emphasis>must</emphasis> use the Internet domain name as
your NIS domain name.</para>
</sect4>
<sect4>
<title>Physical Server Requirements</title>
<para>There are several things to keep in mind when choosing
a machine to use as a NIS server. One of the unfortunate
things about NIS is the level of dependency the clients
have on the server. If a client cannot contact the server
for its NIS domain, very often the machine becomes
unusable. The lack of user and group information causes
most systems to temporarily freeze up. With this in mind
you should make sure to choose a machine that will not be
prone to being rebooted regularly, or one that might be
used for development. The NIS server should ideally be a
stand alone machine whose sole purpose in life is to be an
NIS server. If you have a network that is not very
heavily used, it is acceptable to put the NIS server on a
machine running other services, just keep in mind that if
the NIS server becomes unavailable, it will affect
<emphasis>all</emphasis> of your NIS clients
adversely.</para>
</sect4>
</sect3>
<sect3>
<title>NIS Servers</title>
<para> The canonical copies of all NIS information are stored
on a single machine called the NIS master server. The
databases used to store the information are called NIS maps.
In FreeBSD, these maps are stored in
<filename>/var/yp/[domainname]</filename> where
<filename>[domainname]</filename> is the name of the NIS
domain being served. A single NIS server can support
several domains at once, therefore it is possible to have
several such directories, one for each supported domain.
Each domain will have its own independent set of
maps.</para>
<para>NIS master and slave servers handle all NIS requests
with the <command>ypserv</command> daemon.
<command>ypserv</command> is responsible for receiving
incoming requests from NIS clients, translating the
requested domain and map name to a path to the corresponding
database file and transmitting data from the database back
to the client.</para>
<sect4>
<title>Setting Up a NIS Master Server</title>
<indexterm>
<primary>NIS</primary>
<secondary>server configuration</secondary>
</indexterm>
<para>Setting up a master NIS server can be relatively
straight forward, depending on your needs. FreeBSD comes
with support for NIS out-of-the-box. All you need is to
add the following lines to
<filename>/etc/rc.conf</filename>, and FreeBSD will do the
rest for you.</para>
<procedure>
<step>
<para><programlisting>nisdomainname="test-domain"</programlisting>
This line will set the NIS domainname to
<literal>test-domain</literal>
upon network setup (e.g. after reboot).</para>
</step>
<step>
<para><programlisting>nis_server_enable="YES"</programlisting>
This will tell FreeBSD to start up the NIS server processes
when the networking is next brought up.</para>
</step>
<step>
<para><programlisting>nis_yppasswdd_enable="YES"</programlisting>
This will enable the <command>rpc.yppasswdd</command>
daemon which, as mentioned above, will allow users to
change their NIS password from a client machine.</para>
</step>
</procedure>
<note>
<para>Depending on your NIS setup, you may need to add
further entries. See the <link
linkend="network-nis-server-is-client">section about NIS
servers that are also NIS clients</link>, below, for
details.</para>
</note>
<para>Now, all you have to do is to run the command
<command>/etc/netstart</command> as superuser. It will
set up everything for you, using the values you defined in
<filename>/etc/rc.conf</filename>.</para>
</sect4>
<sect4>
<title>Initializing the NIS Maps</title>
<indexterm>
<primary>NIS</primary>
<secondary>maps</secondary>
</indexterm>
<para>The <emphasis>NIS maps</emphasis> are database files,
that are kept in the <filename>/var/yp</filename>
directory. They are generated from configuration files in
the <filename>/etc</filename> directory of the NIS master,
with one exception: the
<filename>/etc/master.passwd</filename> file. This is for
a good reason, you do not want to propagate passwords to
your <username>root</username> and other administrative
accounts to all the servers in the NIS domain. Therefore,
before we initialize the NIS maps, you should:</para>
<screen>&prompt.root; <userinput>cp /etc/master.passwd /var/yp/master.passwd</userinput>
&prompt.root; <userinput>cd /var/yp</userinput>
&prompt.root; <userinput>vi master.passwd</userinput></screen>
<para>You should remove all entries regarding system
accounts (<username>bin</username>,
<username>tty</username>, <username>kmem</username>,
<username>games</username>, etc), as well as any accounts
that you do not want to be propagated to the NIS clients
(for example <username>root</username> and any other UID 0
(superuser) accounts).</para>
<note><para>Make sure the
<filename>/var/yp/master.passwd</filename> is neither group
nor world readable (mode 600)! Use the
<command>chmod</command> command, if appropriate.</para></note>
<indexterm><primary>Tru64 UNIX</primary></indexterm>
<para>When you have finished, it is time to initialize the
NIS maps! FreeBSD includes a script named
<command>ypinit</command> to do this for you (see its
manual page for more information). Note that this script
is available on most &unix; Operating Systems, but not on
all. On Digital UNIX/Compaq Tru64 UNIX it is called
<command>ypsetup</command>. Because we are generating
maps for an NIS master, we are going to pass the
<option>-m</option> option to <command>ypinit</command>.
To generate the NIS maps, assuming you already performed
the steps above, run:</para>
<screen>ellington&prompt.root; <userinput>ypinit -m test-domain</userinput>
Server Type: MASTER Domain: test-domain
Creating an YP server will require that you answer a few questions.
Questions will all be asked at the beginning of the procedure.
Do you want this procedure to quit on non-fatal errors? [y/n: n] <userinput>n</userinput>
Ok, please remember to go back and redo manually whatever fails.
If you don't, something might not work.
At this point, we have to construct a list of this domains YP servers.
rod.darktech.org is already known as master server.
Please continue to add any slave servers, one per line. When you are
done with the list, type a &lt;control D&gt;.
master server : ellington
next host to add: <userinput>coltrane</userinput>
next host to add: <userinput>^D</userinput>
The current list of NIS servers looks like this:
ellington
coltrane
Is this correct? [y/n: y] <userinput>y</userinput>
[..output from map generation..]
NIS Map update completed.
ellington has been setup as an YP master server without any errors.</screen>
<para><command>ypinit</command> should have created
<filename>/var/yp/Makefile</filename> from
<filename>/var/yp/Makefile.dist</filename>.
When created, this file assumes that you are operating
in a single server NIS environment with only FreeBSD
machines. Since <literal>test-domain</literal> has
a slave server as well, you must edit
<filename>/var/yp/Makefile</filename>:</para>
<screen>ellington&prompt.root; <userinput>vi /var/yp/Makefile</userinput></screen>
<para>You should comment out the line that says</para>
<programlisting>NOPUSH = "True"</programlisting>
<para>(if it is not commented out already).</para>
</sect4>
<sect4>
<title>Setting up a NIS Slave Server</title>
<indexterm>
<primary>NIS</primary>
<secondary>slave server</secondary>
</indexterm>
<para>Setting up an NIS slave server is even more simple than
setting up the master. Log on to the slave server and edit the
file <filename>/etc/rc.conf</filename> as you did before.
The only difference is that we now must use the
<option>-s</option> option when running <command>ypinit</command>.
The <option>-s</option> option requires the name of the NIS
master be passed to it as well, so our command line looks
like:</para>
<screen>coltrane&prompt.root; <userinput>ypinit -s ellington test-domain</userinput>
Server Type: SLAVE Domain: test-domain Master: ellington
Creating an YP server will require that you answer a few questions.
Questions will all be asked at the beginning of the procedure.
Do you want this procedure to quit on non-fatal errors? [y/n: n] <userinput>n</userinput>
Ok, please remember to go back and redo manually whatever fails.
If you don't, something might not work.
There will be no further questions. The remainder of the procedure
should take a few minutes, to copy the databases from ellington.
Transferring netgroup...
ypxfr: Exiting: Map successfully transferred
Transferring netgroup.byuser...
ypxfr: Exiting: Map successfully transferred
Transferring netgroup.byhost...
ypxfr: Exiting: Map successfully transferred
Transferring master.passwd.byuid...
ypxfr: Exiting: Map successfully transferred
Transferring passwd.byuid...
ypxfr: Exiting: Map successfully transferred
Transferring passwd.byname...
ypxfr: Exiting: Map successfully transferred
Transferring group.bygid...
ypxfr: Exiting: Map successfully transferred
Transferring group.byname...
ypxfr: Exiting: Map successfully transferred
Transferring services.byname...
ypxfr: Exiting: Map successfully transferred
Transferring rpc.bynumber...
ypxfr: Exiting: Map successfully transferred
Transferring rpc.byname...
ypxfr: Exiting: Map successfully transferred
Transferring protocols.byname...
ypxfr: Exiting: Map successfully transferred
Transferring master.passwd.byname...
ypxfr: Exiting: Map successfully transferred
Transferring networks.byname...
ypxfr: Exiting: Map successfully transferred
Transferring networks.byaddr...
ypxfr: Exiting: Map successfully transferred
Transferring netid.byname...
ypxfr: Exiting: Map successfully transferred
Transferring hosts.byaddr...
ypxfr: Exiting: Map successfully transferred
Transferring protocols.bynumber...
ypxfr: Exiting: Map successfully transferred
Transferring ypservers...
ypxfr: Exiting: Map successfully transferred
Transferring hosts.byname...
ypxfr: Exiting: Map successfully transferred
coltrane has been setup as an YP slave server without any errors.
Don't forget to update map ypservers on ellington.</screen>
<para>You should now have a directory called
<filename>/var/yp/test-domain</filename>. Copies of the NIS
master server's maps should be in this directory. You will
need to make sure that these stay updated. The following
<filename>/etc/crontab</filename> entries on your slave
servers should do the job:</para>
<programlisting>20 * * * * root /usr/libexec/ypxfr passwd.byname
21 * * * * root /usr/libexec/ypxfr passwd.byuid</programlisting>
<para>These two lines force the slave to sync its maps with
the maps on the master server. Although these entries are
not mandatory, since the master server attempts to ensure
any changes to its NIS maps are communicated to its slaves
and because password information is vital to systems
depending on the server, it is a good idea to force the
updates. This is more important on busy networks where map
updates might not always complete.</para>
<para>Now, run the command <command>/etc/netstart</command> on the
slave server as well, which again starts the NIS server.</para>
</sect4>
</sect3>
<sect3>
<title>NIS Clients</title>
<para> An NIS client establishes what is called a binding to a
particular NIS server using the
<command>ypbind</command> daemon.
<command>ypbind</command> checks the system's default
domain (as set by the <command>domainname</command> command),
and begins broadcasting RPC requests on the local network.
These requests specify the name of the domain for which
<command>ypbind</command> is attempting to establish a binding.
If a server that has been configured to serve the requested
domain receives one of the broadcasts, it will respond to
<command>ypbind</command>, which will record the server's
address. If there are several servers available (a master and
several slaves, for example), <command>ypbind</command> will
use the address of the first one to respond. From that point
on, the client system will direct all of its NIS requests to
that server. <command>ypbind</command> will
occasionally <quote>ping</quote> the server to make sure it is
still up and running. If it fails to receive a reply to one of
its pings within a reasonable amount of time,
<command>ypbind</command> will mark the domain as unbound and
begin broadcasting again in the hopes of locating another
server.</para>
<sect4>
<title>Setting Up a NIS Client</title>
<indexterm>
<primary>NIS</primary>
<secondary>client configuration</secondary>
</indexterm>
<para>Setting up a FreeBSD machine to be a NIS client is fairly
straightforward.</para>
<procedure>
<step>
<para>Edit the file <filename>/etc/rc.conf</filename> and
add the following lines in order to set the NIS domainname
and start <command>ypbind</command> upon network
startup:</para>
<programlisting>nisdomainname="test-domain"
nis_client_enable="YES"</programlisting>
</step>
<step>
<para>To import all possible password entries from the NIS
server, remove all user accounts from your
<filename>/etc/master.passwd</filename> file and use
<command>vipw</command> to add the following line to
the end of the file:</para>
<programlisting>+:::::::::</programlisting>
<note>
<para>This line will afford anyone with a valid account in
the NIS server's password maps an account. There are
many ways to configure your NIS client by changing this
line. See the <link linkend="network-netgroups">netgroups
section</link> below for more information.
For more detailed reading see O'Reilly's book on
<literal>Managing NFS and NIS</literal>.</para>
</note>
<note>
<para>You should keep at least one local account (i.e.
not imported via NIS) in your
<filename>/etc/master.passwd</filename> and this
account should also be a member of the group
<groupname>wheel</groupname>. If there is something
wrong with NIS, this account can be used to log in
remotely, become <username>root</username>, and fix things.</para>
</note>
</step>
<step>
<para>To import all possible group entries from the NIS
server, add this line to your
<filename>/etc/group</filename> file:</para>
<programlisting>+:*::</programlisting>
</step>
</procedure>
<para>After completing these steps, you should be able to run
<command>ypcat passwd</command> and see the NIS server's
passwd map.</para>
</sect4>
</sect3>
</sect2>
<sect2>
<title>NIS Security</title>
<para>In general, any remote user can issue an RPC to
&man.ypserv.8; and retrieve the contents of your NIS maps,
provided the remote user knows your domainname. To prevent
such unauthorized transactions, &man.ypserv.8; supports a
feature called <quote>securenets</quote> which can be used to
restrict access to a given set of hosts. At startup,
&man.ypserv.8; will attempt to load the securenets information
from a file called
<filename>/var/yp/securenets</filename>.</para>
<note>
<para>This path varies depending on the path specified with the
<option>-p</option> option. This file contains entries that
consist of a network specification and a network mask separated
by white space. Lines starting with <quote>#</quote> are
considered to be comments. A sample securenets file might look
like this:</para>
</note>
<programlisting># allow connections from local host -- mandatory
127.0.0.1 255.255.255.255
# allow connections from any host
# on the 192.168.128.0 network
192.168.128.0 255.255.255.0
# allow connections from any host
# between 10.0.0.0 to 10.0.15.255
# this includes the machines in the testlab
10.0.0.0 255.255.240.0</programlisting>
<para>If &man.ypserv.8; receives a request from an address that
matches one of these rules, it will process the request
normally. If the address fails to match a rule, the request
will be ignored and a warning message will be logged. If the
<filename>/var/yp/securenets</filename> file does not exist,
<command>ypserv</command> will allow connections from any
host.</para>
<para>The <command>ypserv</command> program also has support for
Wietse Venema's <application>TCP Wrapper</application> package.
This allows the administrator to use the
<application>TCP Wrapper</application> configuration files for
access control instead of
<filename>/var/yp/securenets</filename>.</para>
<note>
<para>While both of these access control mechanisms provide some
security, they, like the privileged port test, are
vulnerable to <quote>IP spoofing</quote> attacks. All
NIS-related traffic should be blocked at your firewall.</para>
<para>Servers using <filename>/var/yp/securenets</filename>
may fail to serve legitimate NIS clients with archaic TCP/IP
implementations. Some of these implementations set all
host bits to zero when doing broadcasts and/or fail to
observe the subnet mask when calculating the broadcast
address. While some of these problems can be fixed by
changing the client configuration, other problems may force
the retirement of the client systems in question or the
abandonment of <filename>/var/yp/securenets</filename>.</para>
<para>Using <filename>/var/yp/securenets</filename> on a
server with such an archaic implementation of TCP/IP is a
really bad idea and will lead to loss of NIS functionality
for large parts of your network.</para>
<indexterm><primary>TCP Wrappers</primary></indexterm>
<para>The use of the <application>TCP Wrapper</application>
package increases the latency of your NIS server. The
additional delay may be long enough to cause timeouts in
client programs, especially in busy networks or with slow
NIS servers. If one or more of your client systems
suffers from these symptoms, you should convert the client
systems in question into NIS slave servers and force them
to bind to themselves.</para>
</note>
</sect2>
<sect2>
<title>Barring Some Users from Logging On</title>
<para>In our lab, there is a machine <hostid>basie</hostid> that
is supposed to be a faculty only workstation. We do not want
to take this machine out of the NIS domain, yet the
<filename>passwd</filename> file on the master NIS server
contains accounts for both faculty and students. What can we
do?</para>
<para>There is a way to bar specific users from logging on to a
machine, even if they are present in the NIS database. To do
this, all you must do is add
<literal>-<replaceable>username</replaceable></literal> to the
end of the <filename>/etc/master.passwd</filename> file on the
client machine, where <replaceable>username</replaceable> is
the username of the user you wish to bar from logging in.
This should preferably be done using <command>vipw</command>,
since <command>vipw</command> will sanity check your changes
to <filename>/etc/master.passwd</filename>, as well as
automatically rebuild the password database when you finish
editing. For example, if we wanted to bar user
<username>bill</username> from logging on to
<hostid>basie</hostid> we would:</para>
<screen>basie&prompt.root; <userinput>vipw</userinput>
<userinput>[add -bill to the end, exit]</userinput>
vipw: rebuilding the database...
vipw: done
basie&prompt.root; <userinput>cat /etc/master.passwd</userinput>
root:[password]:0:0::0:0:The super-user:/root:/bin/csh
toor:[password]:0:0::0:0:The other super-user:/root:/bin/sh
daemon:*:1:1::0:0:Owner of many system processes:/root:/sbin/nologin
operator:*:2:5::0:0:System &amp;:/:/sbin/nologin
bin:*:3:7::0:0:Binaries Commands and Source,,,:/:/sbin/nologin
tty:*:4:65533::0:0:Tty Sandbox:/:/sbin/nologin
kmem:*:5:65533::0:0:KMem Sandbox:/:/sbin/nologin
games:*:7:13::0:0:Games pseudo-user:/usr/games:/sbin/nologin
news:*:8:8::0:0:News Subsystem:/:/sbin/nologin
man:*:9:9::0:0:Mister Man Pages:/usr/share/man:/sbin/nologin
bind:*:53:53::0:0:Bind Sandbox:/:/sbin/nologin
uucp:*:66:66::0:0:UUCP pseudo-user:/var/spool/uucppublic:/usr/libexec/uucp/uucico
xten:*:67:67::0:0:X-10 daemon:/usr/local/xten:/sbin/nologin
pop:*:68:6::0:0:Post Office Owner:/nonexistent:/sbin/nologin
nobody:*:65534:65534::0:0:Unprivileged user:/nonexistent:/sbin/nologin
+:::::::::
-bill
basie&prompt.root;</screen>
</sect2>
<sect2 id="network-netgroups">
<sect2info>
<authorgroup>
<author>
<firstname>Udo</firstname>
<surname>Erdelhoff</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</sect2info>
<title>Using Netgroups</title>
<indexterm><primary>netgroups</primary></indexterm>
<para>The method shown in the previous section works reasonably
well if you need special rules for a very small number of
users and/or machines. On larger networks, you
<emphasis>will</emphasis> forget to bar some users from logging
onto sensitive machines, or you may even have to modify each
machine separately, thus losing the main benefit of NIS:
<emphasis>centralized</emphasis> administration.</para>
<para>The NIS developers' solution for this problem is called
<emphasis>netgroups</emphasis>. Their purpose and semantics
can be compared to the normal groups used by &unix; file
systems. The main differences are the lack of a numeric ID
and the ability to define a netgroup by including both user
accounts and other netgroups.</para>
<para>Netgroups were developed to handle large, complex networks
with hundreds of users and machines. On one hand, this is
a Good Thing if you are forced to deal with such a situation.
On the other hand, this complexity makes it almost impossible to
explain netgroups with really simple examples. The example
used in the remainder of this section demonstrates this
problem.</para>
<para>Let us assume that your successful introduction of NIS in
your laboratory caught your superiors' interest. Your next
job is to extend your NIS domain to cover some of the other
machines on campus. The two tables contain the names of the
new users and new machines as well as brief descriptions of
them.</para>
<informaltable frame="none" pgwide="1">
<tgroup cols="2">
<thead>
<row>
<entry>User Name(s)</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><username>alpha</username>, <username>beta</username></entry>
<entry>Normal employees of the IT department</entry>
</row>
<row>
<entry><username>charlie</username>, <username>delta</username></entry>
<entry>The new apprentices of the IT department</entry>
</row>
<row>
<entry><username>echo</username>, <username>foxtrott</username>, <username>golf</username>, ...</entry>
<entry>Ordinary employees</entry>
</row>
<row>
<entry><username>able</username>, <username>baker</username>, ...</entry>
<entry>The current interns</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<informaltable frame="none" pgwide="1">
<tgroup cols="2">
<thead>
<row>
<entry>Machine Name(s)</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<!-- Names taken from "Good Omens" by Neil Gaiman and Terry
Pratchett. Many thanks for a brilliant book. -->
<entry><hostid>war</hostid>, <hostid>death</hostid>,
<hostid>famine</hostid>,
<hostid>pollution</hostid></entry>
<entry>Your most important servers. Only the IT
employees are allowed to log onto these
machines.</entry>
</row>
<row>
<!-- gluttony was omitted because it was too fat -->
<entry><hostid>pride</hostid>, <hostid>greed</hostid>,
<hostid>envy</hostid>, <hostid>wrath</hostid>,
<hostid>lust</hostid>, <hostid>sloth</hostid></entry>
<entry>Less important servers. All members of the IT
department are allowed to login onto these
machines.</entry>
</row>
<row>
<entry><hostid>one</hostid>, <hostid>two</hostid>,
<hostid>three</hostid>, <hostid>four</hostid>,
...</entry>
<entry>Ordinary workstations. Only the
<emphasis>real</emphasis> employees are allowed to use
these machines.</entry>
</row>
<row>
<entry><hostid>trashcan</hostid></entry>
<entry>A very old machine without any critical data.
Even the intern is allowed to use this box.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>If you tried to implement these restrictions by separately
blocking each user, you would have to add one
<literal>-<replaceable>user</replaceable></literal> line to
each system's <filename>passwd</filename> for each user who is
not allowed to login onto that system. If you forget just one
entry, you could be in trouble. It may be feasible to do this
correctly during the initial setup, however you
<emphasis>will</emphasis> eventually forget to add the lines
for new users during day-to-day operations. After all, Murphy
was an optimist.</para>
<para>Handling this situation with netgroups offers several
advantages. Each user need not be handled separately; you
assign a user to one or more netgroups and allow or forbid
logins for all members of the netgroup. If you add a new
machine, you will only have to define login restrictions for
netgroups. If a new user is added, you will only have to add
the user to one or more netgroups. Those changes are
independent of each other: no more <quote>for each combination
of user and machine do...</quote> If your NIS setup is planned
carefully, you will only have to modify exactly one central
configuration file to grant or deny access to machines.</para>
<para>The first step is the initialization of the NIS map
netgroup. FreeBSD's &man.ypinit.8; does not create this map by
default, but its NIS implementation will support it once it has
been created. To create an empty map, simply type</para>
<screen>ellington&prompt.root; <userinput>vi /var/yp/netgroup</userinput></screen>
<para>and start adding content. For our example, we need at
least four netgroups: IT employees, IT apprentices, normal
employees and interns.</para>
<programlisting>IT_EMP (,alpha,test-domain) (,beta,test-domain)
IT_APP (,charlie,test-domain) (,delta,test-domain)
USERS (,echo,test-domain) (,foxtrott,test-domain) \
(,golf,test-domain)
INTERNS (,able,test-domain) (,baker,test-domain)</programlisting>
<para><literal>IT_EMP</literal>, <literal>IT_APP</literal> etc.
are the names of the netgroups. Each bracketed group adds
one or more user accounts to it. The three fields inside a
group are:</para>
<orderedlist>
<listitem>
<para>The name of the host(s) where the following items are
valid. If you do not specify a hostname, the entry is
valid on all hosts. If you do specify a hostname, you
will enter a realm of darkness, horror and utter confusion.</para>
</listitem>
<listitem>
<para>The name of the account that belongs to this
netgroup.</para>
</listitem>
<listitem>
<para>The NIS domain for the account. You can import
accounts from other NIS domains into your netgroup if you
are one of the unlucky fellows with more than one NIS
domain.</para>
</listitem>
</orderedlist>
<para>Each of these fields can contain wildcards. See
&man.netgroup.5; for details.</para>
<note>
<indexterm><primary>netgroups</primary></indexterm>
<para>Netgroup names longer than 8 characters should not be
used, especially if you have machines running other
operating systems within your NIS domain. The names are
case sensitive; using capital letters for your netgroup
names is an easy way to distinguish between user, machine
and netgroup names.</para>
<para>Some NIS clients (other than FreeBSD) cannot handle
netgroups with a large number of entries. For example, some
older versions of &sunos; start to cause trouble if a netgroup
contains more than 15 <emphasis>entries</emphasis>. You can
circumvent this limit by creating several sub-netgroups with
15 users or less and a real netgroup that consists of the
sub-netgroups:</para>
<programlisting>BIGGRP1 (,joe1,domain) (,joe2,domain) (,joe3,domain) [...]
BIGGRP2 (,joe16,domain) (,joe17,domain) [...]
BIGGRP3 (,joe31,domain) (,joe32,domain)
BIGGROUP BIGGRP1 BIGGRP2 BIGGRP3</programlisting>
<para>You can repeat this process if you need more than 225
users within a single netgroup.</para>
</note>
<para>Activating and distributing your new NIS map is
easy:</para>
<screen>ellington&prompt.root; <userinput>cd /var/yp</userinput>
ellington&prompt.root; <userinput>make</userinput></screen>
<para>This will generate the three NIS maps
<filename>netgroup</filename>,
<filename>netgroup.byhost</filename> and
<filename>netgroup.byuser</filename>. Use &man.ypcat.1; to
check if your new NIS maps are available:</para>
<screen>ellington&prompt.user; <userinput>ypcat -k netgroup</userinput>
ellington&prompt.user; <userinput>ypcat -k netgroup.byhost</userinput>
ellington&prompt.user; <userinput>ypcat -k netgroup.byuser</userinput></screen>
<para>The output of the first command should resemble the
contents of <filename>/var/yp/netgroup</filename>. The second
command will not produce output if you have not specified
host-specific netgroups. The third command can be used to
get the list of netgroups for a user.</para>
<para>The client setup is quite simple. To configure the server
<hostid>war</hostid>, you only have to start
&man.vipw.8; and replace the line</para>
<programlisting>+:::::::::</programlisting>
<para>with</para>
<programlisting>+@IT_EMP:::::::::</programlisting>
<para>Now, only the data for the users defined in the netgroup
<literal>IT_EMP</literal> is imported into
<hostid>war</hostid>'s password database and only
these users are allowed to login.</para>
<para>Unfortunately, this limitation also applies to the
<literal>~</literal> function of the shell and all routines
converting between user names and numerical user IDs. In
other words, <command>cd
~<replaceable>user</replaceable></command> will not work,
<command>ls -l</command> will show the numerical ID instead of
the username and <command>find . -user joe -print</command>
will fail with <errorname>No such user</errorname>. To fix
this, you will have to import all user entries
<emphasis>without allowing them to login onto your
servers</emphasis>.</para>
<para>This can be achieved by adding another line to
<filename>/etc/master.passwd</filename>. This line should
contain:</para>
<para><literal>+:::::::::/sbin/nologin</literal>, meaning
<quote>Import all entries but replace the shell with
<filename>/sbin/nologin</filename> in the imported
entries</quote>. You can replace any field in the
<literal>passwd</literal> entry by placing a default value in
your <filename>/etc/master.passwd</filename>.</para>
<!-- Been there, done that, got the scars to prove it - ue -->
<warning>
<para>Make sure that the line
<literal>+:::::::::/sbin/nologin</literal> is placed after
<literal>+@IT_EMP:::::::::</literal>. Otherwise, all user
accounts imported from NIS will have <filename>/sbin/nologin</filename> as their
login shell.</para>
</warning>
<para>After this change, you will only have to change one NIS
map if a new employee joins the IT department. You could use
a similar approach for the less important servers by replacing
the old <literal>+:::::::::</literal> in their local version
of <filename>/etc/master.passwd</filename> with something like
this:</para>
<programlisting>+@IT_EMP:::::::::
+@IT_APP:::::::::
+:::::::::/sbin/nologin</programlisting>
<para>The corresponding lines for the normal workstations
could be:</para>
<programlisting>+@IT_EMP:::::::::
+@USERS:::::::::
+:::::::::/sbin/nologin</programlisting>
<para>And everything would be fine until there is a policy
change a few weeks later: The IT department starts hiring
interns. The IT interns are allowed to use the normal
workstations and the less important servers; and the IT
apprentices are allowed to login onto the main servers. You
add a new netgroup <literal>IT_INTERN</literal>, add the new
IT interns to this netgroup and start to change the
configuration on each and every machine... As the old saying
goes: <quote>Errors in centralized planning lead to global
mess</quote>.</para>
<para>NIS' ability to create netgroups from other netgroups can
be used to prevent situations like these. One possibility
is the creation of role-based netgroups. For example, you
could create a netgroup called
<literal>BIGSRV</literal> to define the login
restrictions for the important servers, another netgroup
called <literal>SMALLSRV</literal> for the less
important servers and a third netgroup called
<literal>USERBOX</literal> for the normal
workstations. Each of these netgroups contains the netgroups
that are allowed to login onto these machines. The new
entries for your NIS map netgroup should look like this:</para>
<programlisting>BIGSRV IT_EMP IT_APP
SMALLSRV IT_EMP IT_APP ITINTERN
USERBOX IT_EMP ITINTERN USERS</programlisting>
<para>This method of defining login restrictions works
reasonably well if you can define groups of machines with
identical restrictions. Unfortunately, this is the exception
and not the rule. Most of the time, you will need the ability
to define login restrictions on a per-machine basis.</para>
<para>Machine-specific netgroup definitions are the other
possibility to deal with the policy change outlined above. In
this scenario, the <filename>/etc/master.passwd</filename> of
each box contains two lines starting with <quote>+</quote>.
The first of them adds a netgroup with the accounts allowed to
login onto this machine, the second one adds all other
accounts with <filename>/sbin/nologin</filename> as shell. It
is a good idea to use the <quote>ALL-CAPS</quote> version of
the machine name as the name of the netgroup. In other words,
the lines should look like this:</para>
<programlisting>+@<replaceable>BOXNAME</replaceable>:::::::::
+:::::::::/sbin/nologin</programlisting>
<para>Once you have completed this task for all your machines,
you will not have to modify the local versions of
<filename>/etc/master.passwd</filename> ever again. All
further changes can be handled by modifying the NIS map. Here
is an example of a possible netgroup map for this
scenario with some additional goodies:</para>
<programlisting># Define groups of users first
IT_EMP (,alpha,test-domain) (,beta,test-domain)
IT_APP (,charlie,test-domain) (,delta,test-domain)
DEPT1 (,echo,test-domain) (,foxtrott,test-domain)
DEPT2 (,golf,test-domain) (,hotel,test-domain)
DEPT3 (,india,test-domain) (,juliet,test-domain)
ITINTERN (,kilo,test-domain) (,lima,test-domain)
D_INTERNS (,able,test-domain) (,baker,test-domain)
#
# Now, define some groups based on roles
USERS DEPT1 DEPT2 DEPT3
BIGSRV IT_EMP IT_APP
SMALLSRV IT_EMP IT_APP ITINTERN
USERBOX IT_EMP ITINTERN USERS
#
# And a groups for a special tasks
# Allow echo and golf to access our anti-virus-machine
SECURITY IT_EMP (,echo,test-domain) (,golf,test-domain)
#
# machine-based netgroups
# Our main servers
WAR BIGSRV
FAMINE BIGSRV
# User india needs access to this server
POLLUTION BIGSRV (,india,test-domain)
#
# This one is really important and needs more access restrictions
DEATH IT_EMP
#
# The anti-virus-machine mentioned above
ONE SECURITY
#
# Restrict a machine to a single user
TWO (,hotel,test-domain)
# [...more groups to follow]</programlisting>
<para>If you are using some kind of database to manage your user
accounts, you should be able to create the first part of the
map with your database's report tools. This way, new users
will automatically have access to the boxes.</para>
<para>One last word of caution: It may not always be advisable
to use machine-based netgroups. If you are deploying a couple of
dozen or even hundreds of identical machines for student labs,
you should use role-based netgroups instead of machine-based
netgroups to keep the size of the NIS map within reasonable
limits.</para>
</sect2>
<sect2>
<title>Important Things to Remember</title>
<para>There are still a couple of things that you will need to do
differently now that you are in an NIS environment.</para>
<itemizedlist>
<listitem>
<para>Every time you wish to add a user to the lab, you
must add it to the master NIS server <emphasis>only</emphasis>,
and <emphasis>you must remember to rebuild the NIS
maps</emphasis>. If you forget to do this, the new user will
not be able to login anywhere except on the NIS master.
For example, if we needed to add a new user
<username>jsmith</username> to the lab, we would:</para>
<screen>&prompt.root; <userinput>pw useradd jsmith</userinput>
&prompt.root; <userinput>cd /var/yp</userinput>
&prompt.root; <userinput>make test-domain</userinput></screen>
<para>You could also run <command>adduser jsmith</command> instead
of <command>pw useradd jsmith</command>.</para>
</listitem>
<listitem>
<para><emphasis>Keep the administration accounts out of the
NIS maps</emphasis>. You do not want to be propagating
administrative accounts and passwords to machines that
will have users that should not have access to those
accounts.</para>
</listitem>
<listitem>
<para><emphasis>Keep the NIS master and slave secure, and
minimize their downtime</emphasis>. If somebody either
hacks or simply turns off these machines, they have
effectively rendered many people without the ability to
login to the lab.</para>
<para>This is the chief weakness of any centralized administration
system. If you do
not protect your NIS servers, you will have a lot of angry
users!</para>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>NIS v1 Compatibility</title>
<para> FreeBSD's <application>ypserv</application> has some
support for serving NIS v1 clients. FreeBSD's NIS
implementation only uses the NIS v2 protocol, however other
implementations include support for the v1 protocol for
backwards compatibility with older systems. The
<application>ypbind</application> daemons supplied with these
systems will try to establish a binding to an NIS v1 server
even though they may never actually need it (and they may
persist in broadcasting in search of one even after they
receive a response from a v2 server). Note that while support
for normal client calls is provided, this version of
<application>ypserv</application> does not handle v1 map
transfer requests; consequently, it cannot be used as a master
or slave in conjunction with older NIS servers that only
support the v1 protocol. Fortunately, there probably are not
any such servers still in use today.</para>
</sect2>
<sect2 id="network-nis-server-is-client">
<title>NIS Servers That Are Also NIS Clients</title>
<para> Care must be taken when running
<application>ypserv</application> in a multi-server domain
where the server machines are also NIS clients. It is
generally a good idea to force the servers to bind to
themselves rather than allowing them to broadcast bind
requests and possibly become bound to each other. Strange
failure modes can result if one server goes down and others
are dependent upon it. Eventually all the clients will time
out and attempt to bind to other servers, but the delay
involved can be considerable and the failure mode is still
present since the servers might bind to each other all over
again.</para>
<para>You can force a host to bind to a particular server by running
<command>ypbind</command> with the <option>-S</option>
flag. If you do not want to do this manually each time you
reboot your NIS server, you can add the following lines to
your <filename>/etc/rc.conf</filename>:</para>
<programlisting>nis_client_enable="YES" # run client stuff as well
nis_client_flags="-S <replaceable>NIS domain</replaceable>,<replaceable>server</replaceable>"</programlisting>
<para>See &man.ypbind.8; for further information.</para>
</sect2>
<sect2>
<title>Password Formats</title>
<indexterm>
<primary>NIS</primary>
<secondary>password formats</secondary>
</indexterm>
<para>One of the most common issues that people run into when trying
to implement NIS is password format compatibility. If your NIS
server is using DES encrypted passwords, it will only support
clients that are also using DES. For example, if you have
&solaris; NIS clients in your network, then you will almost certainly
need to use DES encrypted passwords.</para>
<para>To check which format your servers
and clients are using, look at <filename>/etc/login.conf</filename>.
If the host is configured to use DES encrypted passwords, then the
<literal>default</literal> class will contain an entry like this:</para>
<programlisting>default:\
:passwd_format=des:\
:copyright=/etc/COPYRIGHT:\
[Further entries elided]</programlisting>
<para>Other possible values for the <literal>passwd_format</literal>
capability include <literal>blf</literal> and <literal>md5</literal>
(for Blowfish and MD5 encrypted passwords, respectively).</para>
<para>If you have made changes to
<filename>/etc/login.conf</filename>, you will also need to
rebuild the login capability database, which is achieved by
running the following command as
<username>root</username>:</para>
<screen>&prompt.root; <userinput>cap_mkdb /etc/login.conf</userinput></screen>
<note><para>The format of passwords already in
<filename>/etc/master.passwd</filename> will not be updated
until a user changes his password for the first time
<emphasis>after</emphasis> the login capability database is
rebuilt.</para></note>
<para>Next, in order to ensure that passwords are encrypted with
the format that you have chosen, you should also check that
the <literal>crypt_default</literal> in
<filename>/etc/auth.conf</filename> gives precedence to your
chosen password format. To do this, place the format that you
have chosen first in the list. For example, when using DES
encrypted passwords, the entry would be:</para>
<programlisting>crypt_default = des blf md5</programlisting>
<para>Having followed the above steps on each of the &os; based
NIS servers and clients, you can be sure that they all agree
on which password format is used within your network. If you
have trouble authenticating on an NIS client, this is a pretty
good place to start looking for possible problems. Remember:
if you want to deploy an NIS server for a heterogenous
network, you will probably have to use DES on all systems
because it is the lowest common standard.</para>
</sect2>
</sect1>
<sect1 id="network-dhcp">
<sect1info>
<authorgroup>
<author>
<firstname>Greg</firstname>
<surname>Sutter</surname>
<contrib>Written by </contrib>
</author>
</authorgroup>
</sect1info>
<title>Automatic Network Configuration (DHCP)</title>
<sect2>
<title>What Is DHCP?</title>
<indexterm>
<primary>Dynamic Host Configuration Protocol</primary>
<see>DHCP</see>
</indexterm>
<indexterm>
<primary>Internet Software Consortium (ISC)</primary>
</indexterm>
<para>DHCP, the Dynamic Host Configuration Protocol, describes
the means by which a system can connect to a network and obtain the
necessary information for communication upon that network. FreeBSD
versions prior to 6.0 use the ISC (Internet Software
Consortium) DHCP client (&man.dhclient.8;) implementation.
Later versions use the OpenBSD <command>dhclient</command>
taken from OpenBSD&nbsp;3.7. All
information here regarding <command>dhclient</command> is for
use with either of the ISC or OpenBSD DHCP clients. The DHCP
server is the one included in the ISC distribution.</para>
</sect2>
<sect2>
<title>What This Section Covers</title>
<para>This section describes both the client-side components of the ISC and OpenBSD DHCP client and
server-side components of the ISC DHCP system. The
client-side program, <command>dhclient</command>, comes
integrated within FreeBSD, and the server-side portion is
available from the <filename
role="package">net/isc-dhcp3-server</filename> port. The
&man.dhclient.8;, &man.dhcp-options.5;, and
&man.dhclient.conf.5; manual pages, in addition to the
references below, are useful resources.</para>
</sect2>
<sect2>
<title>How It Works</title>
<indexterm><primary>UDP</primary></indexterm>
<para>When <command>dhclient</command>, the DHCP client, is
executed on the client machine, it begins broadcasting
requests for configuration information. By default, these
requests are on UDP port 68. The server replies on UDP 67,
giving the client an IP address and other relevant network
information such as netmask, router, and DNS servers. All of
this information comes in the form of a DHCP
<quote>lease</quote> and is only valid for a certain time
(configured by the DHCP server maintainer). In this manner,
stale IP addresses for clients no longer connected to the
network can be automatically reclaimed.</para>
<para>DHCP clients can obtain a great deal of information from
the server. An exhaustive list may be found in
&man.dhcp-options.5;.</para>
</sect2>
<sect2>
<title>FreeBSD Integration</title>
<para>&os; fully integrates the ISC or OpenBSD DHCP client,
<command>dhclient</command> (according to the &os; version you run). DHCP client support is provided
within both the installer and the base system, obviating the need
for detailed knowledge of network configurations on any network
that runs a DHCP server. <command>dhclient</command> has been
included in all FreeBSD distributions since 3.2.</para>
<indexterm>
<primary><application>sysinstall</application></primary>
</indexterm>
<para>DHCP is supported by
<application>sysinstall</application>. When configuring a
network interface within
<application>sysinstall</application>, the second question
asked is: <quote>Do you want to try DHCP configuration of
the interface?</quote>. Answering affirmatively will
execute <command>dhclient</command>, and if successful, will
fill in the network configuration information
automatically.</para>
<para>There are two things you must do to have your system use
DHCP upon startup:</para>
<indexterm>
<primary>DHCP</primary>
<secondary>requirements</secondary>
</indexterm>
<itemizedlist>
<listitem>
<para>Make sure that the <devicename>bpf</devicename>
device is compiled into your kernel. To do this, add
<literal>device bpf</literal> to your kernel
configuration file, and rebuild the kernel. For more
information about building kernels, see <xref
linkend="kernelconfig"/>.</para> <para>The
<devicename>bpf</devicename> device is already part of
the <filename>GENERIC</filename> kernel that is supplied
with FreeBSD, so if you do not have a custom kernel, you
should not need to create one in order to get DHCP
working.</para>
<note>
<para>For those who are particularly security conscious,
you should be warned that <devicename>bpf</devicename>
is also the device that allows packet sniffers to work
correctly (although they still have to be run as
<username>root</username>). <devicename>bpf</devicename>
<emphasis>is</emphasis> required to use DHCP, but if
you are very sensitive about security, you probably
should not add <devicename>bpf</devicename> to your
kernel in the expectation that at some point in the
future you will be using DHCP.</para>
</note>
</listitem>
<listitem>
<para>Edit your <filename>/etc/rc.conf</filename> to
include the following:</para>
<programlisting>ifconfig_fxp0="DHCP"</programlisting>
<note>
<para>Be sure to replace <literal>fxp0</literal> with the
designation for the interface that you wish to dynamically
configure, as described in
<xref linkend="config-network-setup"/>.</para>
</note>
<para>If you are using a different location for
<command>dhclient</command>, or if you wish to pass additional
flags to <command>dhclient</command>, also include the
following (editing as necessary):</para>
<programlisting>dhcp_program="/sbin/dhclient"
dhcp_flags=""</programlisting>
</listitem>
</itemizedlist>
<indexterm>
<primary>DHCP</primary>
<secondary>server</secondary>
</indexterm>
<para>The DHCP server, <application>dhcpd</application>, is included
as part of the <filename
role="package">net/isc-dhcp3-server</filename> port in the ports
collection. This port contains the ISC DHCP server and
documentation.</para>
</sect2>
<sect2>
<title>Files</title>
<indexterm>
<primary>DHCP</primary>
<secondary>configuration files</secondary>
</indexterm>
<itemizedlist>
<listitem><para><filename>/etc/dhclient.conf</filename></para>
<para><command>dhclient</command> requires a configuration file,
<filename>/etc/dhclient.conf</filename>. Typically the file
contains only comments, the defaults being reasonably sane. This
configuration file is described by the &man.dhclient.conf.5;
manual page.</para>
</listitem>
<listitem><para><filename>/sbin/dhclient</filename></para>
<para><command>dhclient</command> is statically linked and
resides in <filename>/sbin</filename>. The &man.dhclient.8;
manual page gives more information about
<command>dhclient</command>.</para>
</listitem>
<listitem><para><filename>/sbin/dhclient-script</filename></para>
<para><command>dhclient-script</command> is the FreeBSD-specific
DHCP client configuration script. It is described in
&man.dhclient-script.8;, but should not need any user
modification to function properly.</para>
</listitem>
<listitem><para><filename>/var/db/dhclient.leases</filename></para>
<para>The DHCP client keeps a database of valid leases in this
file, which is written as a log. &man.dhclient.leases.5;
gives a slightly longer description.</para>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>Further Reading</title>
<para>The DHCP protocol is fully described in
<ulink url="http://www.freesoft.org/CIE/RFC/2131/">RFC 2131</ulink>.
An informational resource has also been set up at
<ulink url="http://www.dhcp.org/"></ulink>.</para>
</sect2>
<sect2 id="network-dhcp-server">
<title>Installing and Configuring a DHCP Server</title>
<sect3>
<title>What This Section Covers</title>
<para>This section provides information on how to configure
a FreeBSD system to act as a DHCP server using the ISC
(Internet Software Consortium) implementation of the DHCP
server.</para>
<para>The server is not provided as part of
FreeBSD, and so you will need to install the
<filename role="package">net/isc-dhcp3-server</filename>
port to provide this service. See <xref linkend="ports"/> for
more information on using the Ports Collection.</para>
</sect3>
<sect3>
<title>DHCP Server Installation</title>
<indexterm>
<primary>DHCP</primary>
<secondary>installation</secondary>
</indexterm>
<para>In order to configure your FreeBSD system as a DHCP
server, you will need to ensure that the &man.bpf.4;
device is compiled into your kernel. To do this, add
<literal>device bpf</literal> to your kernel
configuration file, and rebuild the kernel. For more
information about building kernels, see <xref
linkend="kernelconfig"/>.</para>
<para>The <devicename>bpf</devicename> device is already
part of the <filename>GENERIC</filename> kernel that is
supplied with FreeBSD, so you do not need to create a custom
kernel in order to get DHCP working.</para>
<note>
<para>Those who are particularly security conscious
should note that <devicename>bpf</devicename>
is also the device that allows packet sniffers to work
correctly (although such programs still need privileged
access). <devicename>bpf</devicename>
<emphasis>is</emphasis> required to use DHCP, but if
you are very sensitive about security, you probably
should not include <devicename>bpf</devicename> in your
kernel purely because you expect to use DHCP at some
point in the future.</para>
</note>
<para>The next thing that you will need to do is edit the sample
<filename>dhcpd.conf</filename> which was installed by the
<filename role="package">net/isc-dhcp3-server</filename> port.
By default, this will be
<filename>/usr/local/etc/dhcpd.conf.sample</filename>, and you
should copy this to
<filename>/usr/local/etc/dhcpd.conf</filename> before proceeding
to make changes.</para>
</sect3>
<sect3>
<title>Configuring the DHCP Server</title>
<indexterm>
<primary>DHCP</primary>
<secondary>dhcpd.conf</secondary>
</indexterm>
<para><filename>dhcpd.conf</filename> is
comprised of declarations regarding subnets and hosts, and is
perhaps most easily explained using an example :</para>
<programlisting>option domain-name "example.com";<co id="domain-name"/>
option domain-name-servers 192.168.4.100;<co id="domain-name-servers"/>
option subnet-mask 255.255.255.0;<co id="subnet-mask"/>
default-lease-time 3600;<co id="default-lease-time"/>
max-lease-time 86400;<co id="max-lease-time"/>
ddns-update-style none;<co id="ddns-update-style"/>
subnet 192.168.4.0 netmask 255.255.255.0 {
range 192.168.4.129 192.168.4.254;<co id="range"/>
option routers 192.168.4.1;<co id="routers"/>
}
host mailhost {
hardware ethernet 02:03:04:05:06:07;<co id="hardware"/>
fixed-address mailhost.example.com;<co id="fixed-address"/>
}</programlisting>
<calloutlist>
<callout arearefs="domain-name">
<para>This option specifies the domain that will be provided
to clients as the default search domain. See
&man.resolv.conf.5; for more information on what this
means.</para>
</callout>
<callout arearefs="domain-name-servers">
<para>This option specifies a comma separated list of DNS
servers that the client should use.</para>
</callout>
<callout arearefs="subnet-mask">
<para>The netmask that will be provided to clients.</para>
</callout>
<callout arearefs="default-lease-time">
<para>A client may request a specific length of time that a
lease will be valid. Otherwise the server will assign
a lease with this expiry value (in seconds).</para>
</callout>
<callout arearefs="max-lease-time">
<para>This is the maximum length of time that the server will
lease for. Should a client request a longer lease, a lease
will be issued, although it will only be valid for
<literal>max-lease-time</literal> seconds.</para>
</callout>
<callout arearefs="ddns-update-style">
<para>This option specifies whether the DHCP server should
attempt to update DNS when a lease is accepted or released.
In the ISC implementation, this option is
<emphasis>required</emphasis>.</para>
</callout>
<callout arearefs="range">
<para>This denotes which IP addresses should be used in
the pool reserved for allocating to clients. IP
addresses between, and including, the ones stated are
handed out to clients.</para>
</callout>
<callout arearefs="routers">
<para>Declares the default gateway that will be provided to
clients.</para>
</callout>
<callout arearefs="hardware">
<para>The hardware MAC address of a host (so that the DHCP server
can recognize a host when it makes a request).</para>
</callout>
<callout arearefs="fixed-address">
<para>Specifies that the host should always be given the
same IP address. Note that using a hostname is
correct here, since the DHCP server will resolve the
hostname itself before returning the lease
information.</para>
</callout>
</calloutlist>
<para>Once you have finished writing your
<filename>dhcpd.conf</filename>,
you should enable the DHCP server in
<filename>/etc/rc.conf</filename>, i.e. by adding:</para>
<programlisting>dhcpd_enable="YES"
dhcpd_ifaces="dc0"</programlisting>
<para>Replace the <literal>dc0</literal> interface name with the
interface (or interfaces, separated by whitespace) that your DHCP
server should listen on for DHCP client requests.</para>
<para>Then, you can proceed to start the server by issuing the
following command:</para>
<screen>&prompt.root; <userinput>/usr/local/etc/rc.d/isc-dhcpd.sh start</userinput></screen>
<para>Should you need to make changes to the configuration of your
server in the future, it is important to note that sending a
<literal>SIGHUP</literal> signal to
<application>dhcpd</application> does <emphasis>not</emphasis>
result in the configuration being reloaded, as it does with most
daemons. You will need to send a <literal>SIGTERM</literal>
signal to stop the process, and then restart it using the command
above.</para>
</sect3>
<sect3>
<title>Files</title>
<indexterm>
<primary>DHCP</primary>
<secondary>configuration files</secondary>
</indexterm>
<itemizedlist>
<listitem><para><filename>/usr/local/sbin/dhcpd</filename></para>
<para><application>dhcpd</application> is statically linked and
resides in <filename>/usr/local/sbin</filename>. The
&man.dhcpd.8; manual page installed with the
port gives more information about
<application>dhcpd</application>.</para>
</listitem>
<listitem><para><filename>/usr/local/etc/dhcpd.conf</filename></para>
<para><application>dhcpd</application> requires a configuration
file, <filename>/usr/local/etc/dhcpd.conf</filename> before it
will start providing service to clients. This file needs to
contain all the information that should be provided to clients
that are being serviced, along with information regarding the
operation of the server. This configuration file is described
by the &man.dhcpd.conf.5; manual page installed
by the port.</para>
</listitem>
<listitem><para><filename>/var/db/dhcpd.leases</filename></para>
<para>The DHCP server keeps a database of leases it has issued
in this file, which is written as a log. The manual page
&man.dhcpd.leases.5;, installed by the port
gives a slightly longer description.</para>
</listitem>
<listitem><para><filename>/usr/local/sbin/dhcrelay</filename></para>
<para><application>dhcrelay</application> is used in advanced
environments where one DHCP server forwards a request from a
client to another DHCP server on a separate network. If you
require this functionality, then install the <filename
role="package">net/isc-dhcp3-relay</filename> port. The
&man.dhcrelay.8; manual page provided with the
port contains more detail.</para>
</listitem>
</itemizedlist>
</sect3>
</sect2>
</sect1>
<sect1 id="network-dns">
<sect1info>
<authorgroup>
<author>
<firstname>Chern</firstname>
<surname>Lee</surname>
<contrib>Contributed by </contrib>
</author>
<author>
<firstname>Tom</firstname>
<surname>Rhodes</surname>
</author>
<author>
<firstname>Daniel</firstname>
<surname>Gerzo</surname>
</author>
</authorgroup>
</sect1info>
<title>Domain Name System (<acronym>DNS</acronym>)</title>
<sect2>
<title>Overview</title>
<indexterm><primary>BIND</primary></indexterm>
<para>&os; utilizes, by default, a version of BIND (Berkeley
Internet Name Domain), which is the most common implementation
of the <acronym>DNS</acronym> protocol. <acronym>DNS</acronym>
is the protocol through which names are mapped to
<acronym>IP</acronym> addresses, and vice versa. For example, a
query for <hostid role="fqdn">www.FreeBSD.org</hostid> will
receive a reply with the <acronym>IP</acronym> address of The
&os; Project's web server, whereas, a query for <hostid
role="fqdn">ftp.FreeBSD.org</hostid> will return the
<acronym>IP</acronym> address of the corresponding
<acronym>FTP</acronym> machine. Likewise, the opposite can
happen. A query for an <acronym>IP</acronym> address can
resolve its hostname. It is not necessary to run a name server
to perform <acronym>DNS</acronym> lookups on a system.</para>
<para>&os; currently comes with <acronym>BIND</acronym>9
<acronym>DNS</acronym> server software by default. Our
installation provides enhanced security features, a new file
system layout and automated &man.chroot.8; configuration.</para>
<indexterm><primary>DNS</primary></indexterm>
<para><acronym>DNS</acronym> is coordinated across the Internet
through a somewhat complex system of authoritative root, Top
Level Domain (<acronym>TLD</acronym>), and other smaller-scale
name servers which host and cache individual domain
information.</para>
<para>Currently, BIND is maintained by the
Internet Software Consortium
<ulink url="http://www.isc.org/"></ulink>.</para>
</sect2>
<sect2>
<title>Terminology</title>
<para>To understand this document, some terms related to
<acronym>DNS</acronym> must be understood.</para>
<indexterm><primary>resolver</primary></indexterm>
<indexterm><primary>reverse DNS</primary></indexterm>
<indexterm><primary>root zone</primary></indexterm>
<informaltable frame="none" pgwide="1">
<tgroup cols="2">
<colspec colwidth="1*"/>
<colspec colwidth="3*"/>
<thead>
<row>
<entry>Term</entry>
<entry>Definition</entry>
</row>
</thead>
<tbody>
<row>
<entry>Forward <acronym>DNS</acronym></entry>
<entry>Mapping of hostnames to IP addresses.</entry>
</row>
<row>
<entry>Origin</entry>
<entry>Refers to the domain covered in a particular zone
file.</entry>
</row>
<row>
<entry><application>named</application>, BIND, name server</entry>
<entry>Common names for the BIND name server package within
&os;.</entry>
</row>
<row>
<entry>Resolver</entry>
<entry>A system process through which a
machine queries a name server for zone information.</entry>
</row>
<row>
<entry>Reverse <acronym>DNS</acronym></entry>
<entry>The opposite of forward <acronym>DNS</acronym>;
mapping of <acronym>IP</acronym> addresses to
hostnames.</entry>
</row>
<row>
<entry>Root zone</entry>
<entry>The beginning of the Internet zone hierarchy.
All zones fall under the root zone, similar to how
all files in a file system fall under the root
directory.</entry>
</row>
<row>
<entry>Zone</entry>
<entry>An individual domain, subdomain, or portion of the
<acronym>DNS</acronym> administered by the same
authority.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<indexterm>
<primary>zones</primary>
<secondary>examples</secondary>
</indexterm>
<para>Examples of zones:</para>
<itemizedlist>
<listitem>
<para><hostid>.</hostid> is the root zone.</para>
</listitem>
<listitem>
<para><hostid>org.</hostid> is a Top Level Domain
(<acronym>TLD</acronym>) under the root zone.</para>
</listitem>
<listitem>
<para><hostid role="domainname">example.org.</hostid> is a
zone under the <hostid>org.</hostid>
<acronym>TLD</acronym>.</para>
</listitem>
<listitem>
<para><hostid>1.168.192.in-addr.arpa</hostid> is a zone
referencing all <acronym>IP</acronym> addresses which fall
under the <hostid role="ipaddr">192.168.1.*</hostid>
<acronym>IP</acronym> space.</para>
</listitem>
</itemizedlist>
<para>As one can see, the more specific part of a hostname appears
to its left. For example, <hostid
role="domainname">example.org.</hostid> is more specific than
<hostid>org.</hostid>, as <hostid>org.</hostid> is more specific
than the root zone. The layout of each part of a hostname is
much like a file system: the
<filename class="directory">/dev</filename> directory falls
within the root, and so on.</para>
</sect2>
<sect2>
<title>Reasons to Run a Name Server</title>
<para>Name servers usually come in two forms: an authoritative
name server, and a caching name server.</para>
<para>An authoritative name server is needed when:</para>
<itemizedlist>
<listitem>
<para>One wants to serve <acronym>DNS</acronym> information to
the world, replying authoritatively to queries.</para>
</listitem>
<listitem>
<para>A domain, such as <hostid
role="domainname">example.org</hostid>, is registered and
<acronym>IP</acronym> addresses need to be assigned to
hostnames under it.</para>
</listitem>
<listitem>
<para>An <acronym>IP</acronym> address block requires reverse
<acronym>DNS</acronym> entries (<acronym>IP</acronym> to
hostname).</para>
</listitem>
<listitem>
<para>A backup or second name server, called a slave, will
reply to queries.</para>
</listitem>
</itemizedlist>
<para>A caching name server is needed when:</para>
<itemizedlist>
<listitem>
<para>A local <acronym>DNS</acronym> server may cache and
respond more quickly than querying an outside name
server.</para>
</listitem>
</itemizedlist>
<para>When one queries for <hostid
role="fqdn">www.FreeBSD.org</hostid>, the resolver usually
queries the uplink <acronym>ISP</acronym>'s name server, and
retrieves the reply. With a local, caching
<acronym>DNS</acronym> server, the query only has to be made
once to the outside world by the caching <acronym>DNS</acronym>
server. Every additional query will not have to look to the
outside of the local network, since the information is cached
locally.</para>
</sect2>
<sect2>
<title>How It Works</title>
<para>In &os;, the BIND daemon is called
<application>named</application> for obvious reasons.</para>
<informaltable frame="none" pgwide="1">
<tgroup cols="2">
<thead>
<row>
<entry>File</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>&man.named.8;</entry>
<entry>The BIND daemon.</entry>
</row>
<row>
<entry>&man.rndc.8;</entry>
<entry>Name server control utility.</entry>
</row>
<row>
<entry><filename class="directory">/etc/namedb</filename></entry>
<entry>Directory where BIND zone information resides.</entry>
</row>
<row>
<entry><filename>/etc/namedb/named.conf</filename></entry>
<entry>Configuration file of the daemon.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>Depending on how a given zone is configured on the server,
the files related to that zone can be found in the <filename
class="directory">master</filename>, <filename
class="directory">slave</filename>, or <filename
class="directory">dynamic</filename> subdirectories of the
<filename class="directory">/etc/namedb</filename> directory.
These files contain the <acronym>DNS</acronym> information that
will be given out by the name server in response to queries.</para>
</sect2>
<sect2>
<title>Starting BIND</title>
<indexterm>
<primary>BIND</primary>
<secondary>starting</secondary>
</indexterm>
<para>Since BIND is installed by default, configuring it all is
relatively simple.</para>
<para>The default <application>named</application> configuration
is that of a basic resolving name server, ran in a
&man.chroot.8; environment. To start the server one time with
this configuration, use the following command:</para>
<screen>&prompt.root; <userinput>/etc/rc.d/named forcestart</userinput></screen>
<para>To ensure the <application>named</application> daemon is
started at boot each time, put the following line into the
<filename>/etc/rc.conf</filename>:</para>
<programlisting>named_enable="YES"</programlisting>
<para>There are obviously many configuration options for
<filename>/etc/namedb/named.conf</filename> that are beyond the
scope of this document. However, if you are interested in the
startup options for <application>named</application> on &os;,
take a look at the
<literal>named_<replaceable>*</replaceable></literal> flags in
<filename>/etc/defaults/rc.conf</filename> and consult the
&man.rc.conf.5; manual page. The
<xref linkend="configtuning-rcd"/> section is also a good read.</para>
</sect2>
<sect2>
<title>Configuration Files</title>
<indexterm>
<primary>BIND</primary>
<secondary>configuration files</secondary>
</indexterm>
<para>Configuration files for <application>named</application>
currently reside in
<filename class="directory">/etc/namedb</filename> directory and
will need modification before use, unless all that is needed is
a simple resolver. This is where most of the configuration will
be performed.</para>
<sect3>
<title>Using <command>make-localhost</command></title>
<para>To configure a master zone for the localhost visit the
<filename class="directory">/etc/namedb</filename> directory
and run the following command:</para>
<screen>&prompt.root; <userinput>sh make-localhost</userinput></screen>
<para>If all went well, a new file should exist in the
<filename class="directory">master</filename> subdirectory.
The filenames should be <filename>localhost.rev</filename> for
the local domain name and <filename>localhost-v6.rev</filename>
for <acronym>IPv6</acronym> configurations. As the default
configuration file, required information will
be present in the <filename>named.conf</filename> file.</para>
</sect3>
<sect3>
<title><filename>/etc/namedb/named.conf</filename></title>
<programlisting>// &dollar;FreeBSD&dollar;
//
// Refer to the named.conf(5) and named(8) man pages, and the documentation
// in /usr/share/doc/bind9 for more details.
//
// If you are going to set up an authoritative server, make sure you
// understand the hairy details of how DNS works. Even with
// simple mistakes, you can break connectivity for affected parties,
// or cause huge amounts of useless Internet traffic.
options {
directory "/etc/namedb";
pid-file "/var/run/named/pid";
dump-file "/var/dump/named_dump.db";
statistics-file "/var/stats/named.stats";
// If named is being used only as a local resolver, this is a safe default.
// For named to be accessible to the network, comment this option, specify
// the proper IP address, or delete this option.
listen-on { 127.0.0.1; };
// If you have IPv6 enabled on this system, uncomment this option for
// use as a local resolver. To give access to the network, specify
// an IPv6 address, or the keyword "any".
// listen-on-v6 { ::1; };
// In addition to the "forwarders" clause, you can force your name
// server to never initiate queries of its own, but always ask its
// forwarders only, by enabling the following line:
//
// forward only;
// If you've got a DNS server around at your upstream provider, enter
// its IP address here, and enable the line below. This will make you
// benefit from its cache, thus reduce overall DNS traffic in the Internet.
/*
forwarders {
127.0.0.1;
};
*/</programlisting>
<para>Just as the comment says, to benefit from an uplink's
cache, <literal>forwarders</literal> can be enabled here.
Under normal circumstances, a name server will recursively
query the Internet looking at certain name servers until it
finds the answer it is looking for. Having this enabled will
have it query the uplink's name server (or name server
provided) first, taking advantage of its cache. If the uplink
name server in question is a heavily trafficked, fast name
server, enabling this may be worthwhile.</para>
<warning>
<para><hostid role="ipaddr">127.0.0.1</hostid> will
<emphasis>not</emphasis> work here. Change this
<acronym>IP</acronym> address to a name server at your
uplink.</para>
</warning>
<programlisting> /*
* If there is a firewall between you and nameservers you want
* to talk to, you might need to uncomment the query-source
* directive below. Previous versions of BIND always asked
* questions using port 53, but BIND versions 8 and later
* use a pseudo-random unprivileged UDP port by default.
*/
// query-source address * port 53;
};
// If you enable a local name server, don't forget to enter 127.0.0.1
// first in your /etc/resolv.conf so this server will be queried.
// Also, make sure to enable it in /etc/rc.conf.
zone "." {
type hint;
file "named.root";
};
zone "0.0.127.IN-ADDR.ARPA" {
type master;
file "master/localhost.rev";
};
// RFC 3152
zone "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA" {
type master;
file "master/localhost-v6.rev";
};
// NB: Do not use the IP addresses below, they are faked, and only
// serve demonstration/documentation purposes!
//
// Example slave zone config entries. It can be convenient to become
// a slave at least for the zone your own domain is in. Ask
// your network administrator for the IP address of the responsible
// primary.
//
// Never forget to include the reverse lookup (IN-ADDR.ARPA) zone!
// (This is named after the first bytes of the IP address, in reverse
// order, with ".IN-ADDR.ARPA" appended.)
//
// Before starting to set up a primary zone, make sure you fully
// understand how DNS and BIND works. There are sometimes
// non-obvious pitfalls. Setting up a slave zone is simpler.
//
// NB: Don't blindly enable the examples below. :-) Use actual names
// and addresses instead.
/* An example master zone
zone "example.net" {
type master;
file "master/example.net";
};
*/
/* An example dynamic zone
key "exampleorgkey" {
algorithm hmac-md5;
secret "sf87HJqjkqh8ac87a02lla==";
};
zone "example.org" {
type master;
allow-update {
key "exampleorgkey";
};
file "dynamic/example.org";
};
*/
/* Examples of forward and reverse slave zones
zone "example.com" {
type slave;
file "slave/example.com";
masters {
192.168.1.1;
};
};
zone "1.168.192.in-addr.arpa" {
type slave;
file "slave/1.168.192.in-addr.arpa";
masters {
192.168.1.1;
};
};
*/</programlisting>
<para>In <filename>named.conf</filename>, these are examples of
slave entries for a forward and reverse zone.</para>
<para>For each new zone served, a new zone entry must be added
to <filename>named.conf</filename>.</para>
<para>For example, the simplest zone entry for
<hostid role="domainname">example.org</hostid> can look
like:</para>
<programlisting>zone "example.org" {
type master;
file "master/example.org";
};</programlisting>
<para>The zone is a master, as indicated by the
<option>type</option> statement, holding its zone information
in <filename>/etc/namedb/master/example.org</filename>
indicated by the <option>file</option> statement.</para>
<programlisting>zone "example.org" {
type slave;
file "slave/example.org";
};</programlisting>
<para>In the slave case, the zone information is transferred
from the master name server for the particular zone, and saved
in the file specified. If and when the master server dies or
is unreachable, the slave name server will have the
transferred zone information and will be able to serve
it.</para>
</sect3>
<sect3>
<title>Zone Files</title>
<indexterm>
<primary>BIND</primary>
<secondary>zone files</secondary>
</indexterm>
<para>An example master zone file for <hostid
role="domainname">example.org</hostid> (existing within
<filename>/etc/namedb/master/example.org</filename>) is as
follows:</para>
<programlisting>&dollar;TTL 3600 ; 1 hour
example.org. IN SOA ns1.example.org. admin.example.org. (
2006051501 ; Serial
10800 ; Refresh
3600 ; Retry
604800 ; Expire
86400 ; Minimum TTL
)
; DNS Servers
IN NS ns1.example.org.
IN NS ns2.example.org.
; MX Records
IN MX 10 mx.example.org.
IN MX 20 mail.example.org.
IN A 192.168.1.1
; Machine Names
localhost IN A 127.0.0.1
ns1 IN A 192.168.1.2
ns2 IN A 192.168.1.3
mx IN A 192.168.1.4
mail IN A 192.168.1.5
; Aliases
www IN CNAME @</programlisting>
<para>
Note that every hostname ending in a <quote>.</quote> is an
exact hostname, whereas everything without a trailing
<quote>.</quote> is referenced to the origin. For example,
<literal>www</literal> is translated into
<literal>www.<replaceable>origin</replaceable></literal>.
In our fictitious zone file, our origin is
<hostid>example.org.</hostid>, so <literal>www</literal>
would translate to <hostid>www.example.org.</hostid>
</para>
<para>
The format of a zone file follows:
</para>
<programlisting>recordname IN recordtype value</programlisting>
<indexterm>
<primary>DNS</primary>
<secondary>records</secondary>
</indexterm>
<para>
The most commonly used DNS records:
</para>
<variablelist>
<varlistentry>
<term>SOA</term>
<listitem><para>start of zone authority</para></listitem>
</varlistentry>
<varlistentry>
<term>NS</term>
<listitem><para>an authoritative name server</para></listitem>
</varlistentry>
<varlistentry>
<term>A</term>
<listitem><para>a host address</para></listitem>
</varlistentry>
<varlistentry>
<term>CNAME</term>
<listitem><para>the canonical name for an alias</para></listitem>
</varlistentry>
<varlistentry>
<term>MX</term>
<listitem><para>mail exchanger</para></listitem>
</varlistentry>
<varlistentry>
<term>PTR</term>
<listitem><para>a domain name pointer (used in reverse DNS)
</para></listitem>
</varlistentry>
</variablelist>
<programlisting>
example.org. IN SOA ns1.example.org. admin.example.org. (
2006051501 ; Serial
10800 ; Refresh after 3 hours
3600 ; Retry after 1 hour
604800 ; Expire after 1 week
86400 ) ; Minimum TTL of 1 day</programlisting>
<variablelist>
<varlistentry>
<term><hostid role="domainname">example.org.</hostid></term>
<listitem><para>the domain name, also the origin for this
zone file.</para></listitem>
</varlistentry>
<varlistentry>
<term><hostid role="fqdn">ns1.example.org.</hostid></term>
<listitem><para>the primary/authoritative name server for this
zone.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>admin.example.org.</literal></term>
<listitem><para>the responsible person for this zone,
email address with <quote>@</quote>
replaced. (<email>admin@example.org</email> becomes
<literal>admin.example.org</literal>)</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>2006051501</literal></term>
<listitem><para>the serial number of the file. This
must be incremented each time the zone file is
modified. Nowadays, many admins prefer a
<literal>yyyymmddrr</literal> format for the serial
number. <literal>2006051501</literal> would mean
last modified 05/15/2006, the latter
<literal>01</literal> being the first time the zone
file has been modified this day. The serial number
is important as it alerts slave name servers for a
zone when it is updated.</para>
</listitem>
</varlistentry>
</variablelist>
<programlisting>
IN NS ns1.example.org.</programlisting>
<para>
This is an NS entry. Every name server that is going to reply
authoritatively for the zone must have one of these entries.
</para>
<programlisting>
localhost IN A 127.0.0.1
ns1 IN A 192.168.1.2
ns2 IN A 192.168.1.3
mx IN A 192.168.1.4
mail IN A 192.168.1.5</programlisting>
<para>
The A record indicates machine names. As seen above,
<hostid role="fqdn">ns1.example.org</hostid> would resolve
to <hostid role="ipaddr">192.168.1.2</hostid>.
</para>
<programlisting>
IN A 192.168.1.1</programlisting>
<para>This line assigns IP address
<hostid role="ipaddr">192.168.1.1</hostid> to the current origin,
in this case <hostid role="domainname">example.org</hostid>.</para>
<programlisting>
www IN CNAME @</programlisting>
<para>
The canonical name record is usually used for giving aliases
to a machine. In the example, <hostid>www</hostid> is
aliased to the <quote>master</quote> machine which name equals
to domain name <hostid role="domainname">example.org</hostid>
(<hostid role="ipaddr">192.168.1.1</hostid>).
CNAMEs can be used to provide alias
hostnames, or round robin one hostname among multiple
machines.
</para>
<indexterm>
<primary>MX record</primary>
</indexterm>
<programlisting>
IN MX 10 mail.example.org.</programlisting>
<para>
The MX record indicates which mail
servers are responsible for handling incoming mail for the
zone. <hostid role="fqdn">mail.example.org</hostid> is the
hostname of the mail server, and 10 being the priority of
that mail server.
</para>
<para>
One can have several mail servers, with priorities of 10,
20 and so on. A mail server attempting to deliver to <hostid
role="domainname">example.org</hostid> would first try the
highest priority MX (the record with the lowest priority
number), then the second highest, etc, until the mail can be
properly delivered.
</para>
<para>
For in-addr.arpa zone files (reverse DNS), the same format is
used, except with PTR entries instead of
A or CNAME.
</para>
<programlisting>$TTL 3600
1.168.192.in-addr.arpa. IN SOA ns1.example.org. admin.example.org. (
2006051501 ; Serial
10800 ; Refresh
3600 ; Retry
604800 ; Expire
3600 ) ; Minimum
IN NS ns1.example.org.
IN NS ns2.example.org.
1 IN PTR example.org.
2 IN PTR ns1.example.org.
3 IN PTR ns2.example.org.
4 IN PTR mx.example.org.
5 IN PTR mail.example.org.</programlisting>
<para>This file gives the proper IP address to hostname
mappings of our above fictitious domain.</para>
</sect3>
</sect2>
<sect2>
<title>Caching Name Server</title>
<indexterm>
<primary>BIND</primary>
<secondary>caching name server</secondary>
</indexterm>
<para>A caching name server is a name server that is not
authoritative for any zones. It simply asks queries of its
own, and remembers them for later use. To set one up, just
configure the name server as usual, omitting any inclusions of
zones.</para>
</sect2>
<sect2>
<title>Security</title>
<para>Although BIND is the most common implementation of DNS,
there is always the issue of security. Possible and
exploitable security holes are sometimes found.
</para>
<para>While &os; automatically drops
<application>named</application> into a &man.chroot.8;
environment; there are several other security mechanisms in
place which could help to lure off possible
<acronym>DNS</acronym> service attacks.</para>
<para>It is always good idea to read <ulink
url="http://www.cert.org/">CERT</ulink>'s security advisories
and to subscribe to the &a.security-notifications; to stay up to
date with the current Internet and &os; security issues.</para>
<tip>
<para>If a problem arises, keeping sources up to date and
having a fresh build of <application>named</application> would
not hurt.</para>
</tip>
</sect2>
<sect2>
<title>Further Reading</title>
<para>BIND/<application>named</application> manual pages:
&man.rndc.8; &man.named.8; &man.named.conf.5;</para>
<itemizedlist>
<listitem>
<para><ulink
url="http://www.isc.org/products/BIND/">Official ISC BIND
Page</ulink></para>
</listitem>
<listitem>
<para><ulink
url="http://www.isc.org/sw/guild/bf/">Official ISC BIND
Forum</ulink></para>
</listitem>
<listitem>
<para><ulink
url="http://www.nominum.com/getOpenSourceResource.php?id=6">
BIND FAQ</ulink></para>
</listitem>
<listitem>
<para><ulink url="http://www.oreilly.com/catalog/dns5/">O'Reilly
DNS and BIND 5th Edition</ulink></para>
</listitem>
<listitem>
<para><ulink
url="ftp://ftp.isi.edu/in-notes/rfc1034.txt">RFC1034
- Domain Names - Concepts and Facilities</ulink></para>
</listitem>
<listitem>
<para><ulink
url="ftp://ftp.isi.edu/in-notes/rfc1035.txt">RFC1035
- Domain Names - Implementation and Specification</ulink></para>
</listitem>
</itemizedlist>
</sect2>
</sect1>
<sect1 id="network-apache">
<sect1info>
<authorgroup>
<author>
<firstname>Murray</firstname>
<surname>Stokely</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</sect1info>
<title>Apache HTTP Server</title>
<indexterm><primary>web servers</primary>
<secondary>setting up</secondary></indexterm>
<indexterm><primary>Apache</primary></indexterm>
<sect2>
<title>Overview</title>
<para>&os; is used to run some of the busiest web sites in the
world. The majority of web servers on the Internet are using
the <application>Apache HTTP Server</application>.
<application>Apache</application> software packages should be
included on your FreeBSD installation media. If you did not
install <application>Apache</application> when you first
installed FreeBSD, then you can install it from the <filename
role="package">www/apache13</filename> or <filename
role="package">www/apache20</filename> port.</para>
<para>Once <application>Apache</application> has been installed
successfully, it must be configured.</para>
<note><para>This section covers version 1.3.X of the
<application>Apache HTTP Server</application> as that is the
most widely used version for &os;. <application>Apache</application>&nbsp;2.X introduces many
new technologies but they are not discussed here. For more
information about <application>Apache</application>&nbsp;2.X, please see <ulink
url="http://httpd.apache.org/"></ulink>.</para></note>
</sect2>
<sect2>
<title>Configuration</title>
<indexterm><primary>Apache</primary>
<secondary>configuration file</secondary></indexterm>
<para>The main <application>Apache HTTP Server</application> configuration file is
installed as
<filename>/usr/local/etc/apache/httpd.conf</filename> on &os;.
This file is a typical &unix; text configuration file with
comment lines beginning with the <literal>#</literal>
character. A comprehensive description of all possible
configuration options is outside the scope of this book, so
only the most frequently modified directives will be described
here.</para>
<variablelist>
<varlistentry>
<term><literal>ServerRoot "/usr/local"</literal></term>
<listitem>
<para>This specifies the default directory hierarchy for
the <application>Apache</application> installation. Binaries are stored in the
<filename class="directory">bin</filename> and
<filename class="directory">sbin</filename> subdirectories
of the server root, and configuration files are stored in
<filename class="directory">etc/apache</filename>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ServerAdmin you@your.address</literal></term>
<listitem>
<para>The address to which problems with the server should
be emailed. This address appears on some
server-generated pages, such as error documents.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ServerName www.example.com</literal></term>
<listitem>
<para><literal>ServerName</literal> allows you to set a host name which is
sent back to clients for your server if it is different
to the one that the host is configured with (i.e., use <hostid>www</hostid>
instead of the host's real name).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DocumentRoot "/usr/local/www/data"</literal></term>
<listitem>
<para><literal>DocumentRoot</literal>: The directory out of which you will
serve your documents. By default, all requests are taken
from this directory, but symbolic links and aliases may
be used to point to other locations.</para>
</listitem>
</varlistentry>
</variablelist>
<para>It is always a good idea to make backup copies of your
<application>Apache</application> configuration file before making changes. Once you are
satisfied with your initial configuration you are ready to
start running <application>Apache</application>.</para>
<!-- sect3 for performance tuning directives? maxservers minservers -->
<!-- etc..?? -->
<!-- Advanced configuration section.
Performance tuning directives.
Log file format -->
</sect2>
<sect2>
<title>Running <application>Apache</application></title>
<indexterm><primary>Apache</primary>
<secondary>starting or stopping</secondary></indexterm>
<para><application>Apache</application> does not run from the
<application>inetd</application> super server as many other
network servers do. It is configured to run standalone for
better performance for incoming HTTP requests from client web
browsers. A shell script wrapper is included to make
starting, stopping, and restarting the server as simple as
possible. To start up <application>Apache</application> for
the first time, just run:</para>
<screen>&prompt.root; <userinput>/usr/local/sbin/apachectl start</userinput></screen>
<para>You can stop the server at any time by typing:</para>
<screen>&prompt.root; <userinput>/usr/local/sbin/apachectl stop</userinput></screen>
<para>After making changes to the configuration file for any
reason, you will need to restart the server:</para>
<screen>&prompt.root; <userinput>/usr/local/sbin/apachectl restart</userinput></screen>
<para>To restart <application>Apache</application> without
aborting current connections, run:</para>
<screen>&prompt.root; <userinput>/usr/local/sbin/apachectl graceful</userinput></screen>
<para>Additional information available at
&man.apachectl.8; manual page.</para>
<para>To launch <application>Apache</application> at system
startup, add the following line to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>apache_enable="YES"</programlisting>
<para>If you would like to supply additional command line
options for the <application>Apache</application>
<command>httpd</command> program started at system boot, you
may specify them with an additional line in
<filename>rc.conf</filename>:</para>
<programlisting>apache_flags=""</programlisting>
<para>Now that the web server is running, you can view your web
site by pointing a web browser to
<literal>http://localhost/</literal>. The default web page
that is displayed is
<filename>/usr/local/www/data/index.html</filename>.</para>
</sect2>
<sect2>
<title>Virtual Hosting</title>
<para><application>Apache</application> supports two different
types of Virtual Hosting. The first method is Name-based
Virtual Hosting. Name-based virtual hosting uses the clients
HTTP/1.1 headers to figure out the hostname. This allows many
different domains to share the same IP address.</para>
<para>To setup <application>Apache</application> to use
Name-based Virtual Hosting add an entry like the following to
your <filename>httpd.conf</filename>:</para>
<programlisting>NameVirtualHost *</programlisting>
<para>If your webserver was named <hostid role="fqdn">www.domain.tld</hostid> and
you wanted to setup a virtual domain for
<hostid role="fqdn">www.someotherdomain.tld</hostid> then you would add
the following entries to
<filename>httpd.conf</filename>:</para>
<screen>&lt;VirtualHost *&gt;
ServerName www.domain.tld
DocumentRoot /www/domain.tld
&lt;/VirtualHost&gt;
&lt;VirtualHost *&gt;
ServerName www.someotherdomain.tld
DocumentRoot /www/someotherdomain.tld
&lt;/VirtualHost&gt;</screen>
<para>Replace the addresses with the addresses you want to use
and the path to the documents with what you are using.</para>
<para>For more information about setting up virtual hosts,
please consult the official <application>Apache</application>
documentation at: <ulink
url="http://httpd.apache.org/docs/vhosts/"></ulink>.</para>
</sect2>
<sect2>
<title>Apache Modules</title>
<indexterm><primary>Apache</primary>
<secondary>modules</secondary></indexterm>
<para>There are many different <application>Apache</application> modules available to add
functionality to the basic server. The FreeBSD Ports
Collection provides an easy way to install
<application>Apache</application> together with some of the
more popular add-on modules.</para>
<sect3>
<title>mod_ssl</title>
<indexterm><primary>web servers</primary>
<secondary>secure</secondary></indexterm>
<indexterm><primary>SSL</primary></indexterm>
<indexterm><primary>cryptography</primary></indexterm>
<para>The <application>mod_ssl</application> module uses the OpenSSL library to provide
strong cryptography via the Secure Sockets Layer (SSL v2/v3)
and Transport Layer Security (TLS v1) protocols. This
module provides everything necessary to request a signed
certificate from a trusted certificate signing authority so
that you can run a secure web server on &os;.</para>
<para>If you have not yet installed
<application>Apache</application>, then a version of <application>Apache</application>
1.3.X that includes <application>mod_ssl</application> may be installed with the <filename
role="package">www/apache13-modssl</filename> port. SSL
support is also available for <application>Apache</application>&nbsp;2.X in the
<filename role="package">www/apache20</filename> port,
where it is enabled by default.</para>
<!-- XXX add more information about configuring mod_ssl here. -->
<!-- Generating keys, getting the key signed, setting up your secure -->
<!-- web server! -->
</sect3>
<sect3>
<title>Dynamic Websites with Perl &amp; PHP</title>
<para>In the past few years, more businesses have turned to the
Internet in order to enhance their revenue and increase
exposure. This has also increased the need for interactive
web content. While some companies, such as &microsoft;, have
introduced solutions into their proprietary products, the
open source community answered the call. Two options for
dynamic web content include
<application>mod_perl</application> &amp;
<application>mod_php</application>.</para>
<sect4>
<title>mod_perl</title>
<indexterm>
<primary>mod_perl</primary>
<secondary>Perl</secondary>
</indexterm>
<para>The <application>Apache</application>/Perl integration project brings together the
full power of the Perl programming language and the <application>Apache
HTTP Server</application>. With the <application>mod_perl</application> module it is possible to
write <application>Apache</application> modules entirely in Perl. In addition, the
persistent interpreter embedded in the server avoids the
overhead of starting an external interpreter and the penalty
of Perl start-up time.</para>
<para><application>mod_perl</application> is available a few
different ways. To use <application>mod_perl</application>
remember that <application>mod_perl</application> 1.0 only
works with <application>Apache</application> 1.3 and
<application>mod_perl</application> 2.0 only works with
<application>Apache</application> 2.
<application>mod_perl</application> 1.0 is available in
<filename role="package">www/mod_perl</filename> and a
statically compiled version is available in
<filename role="package">www/apache13-modperl</filename>.
<application>mod_perl</application> 2.0 is avaliable in
<filename role="package">www/mod_perl2</filename>.</para>
</sect4>
<sect4>
<sect4info>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Rhodes</surname>
<contrib>Written by </contrib>
</author>
</authorgroup>
</sect4info>
<title>mod_php</title>
<indexterm>
<primary>mod_php</primary>
<secondary>PHP</secondary>
</indexterm>
<para><acronym>PHP</acronym>, also known as <quote>PHP:
Hypertext Preprocessor</quote> is a general-purpose scripting
language that is especially suited for Web development.
Capable of being embedded into <acronym>HTML</acronym> its
syntax draws upon C, &java;, and Perl with the intention of
allowing web developers to write dynamically generated
webpages quickly.</para>
<para>To gain support for <acronym>PHP</acronym>5 for the
<application>Apache</application> web server, begin by
installing the
<filename role="package">www/mod_php5</filename>
port.</para>
<para>This will install and configure the modules required
to support dynamic <acronym>PHP</acronym> applications. Check
to ensure the following sections have been added to
<filename>/usr/local/etc/apache/httpd.conf</filename>:</para>
<programlisting>LoadModule php5_module libexec/apache/libphp5.so</programlisting>
<programlisting>AddModule mod_php5.c
&lt;IfModule mod_php5.c&gt;
DirectoryIndex index.php index.html
&lt;/IfModule&gt;
&lt;IfModule mod_php5.c&gt;
AddType application/x-httpd-php .php
AddType application/x-httpd-php-source .phps
&lt;/IfModule&gt;</programlisting>
<para>Once completed, a simple call to the
<command>apachectl</command> command for a graceful
restart is needed to load the <acronym>PHP</acronym>
module:</para>
<screen>&prompt.root; <userinput>apachectl graceful</userinput></screen>
<para>The <acronym>PHP</acronym> support in &os; is extremely
modular so the base install is very limited. It is very easy
to add support using the
<filename role="package">lang/php5-extensions</filename> port.
This port provides a menu driven interface to
<acronym>PHP</acronym> extension installation.
Alternatively, individual extensions can be installed using
the appropriate port.</para>
<para>For instance, to add support for the
<application>MySQL</application> database server to
<acronym>PHP</acronym>5, simply install the
<filename role="package">databases/php5-mysql</filename>
port.</para>
<para>After installing an extension, the
<application>Apache</application> server must be reloaded to
pick up the new configuration changes:</para>
<screen>&prompt.root; <userinput>apachectl graceful</userinput></screen>
</sect4>
</sect3>
</sect2>
</sect1>
<sect1 id="network-ftp">
<sect1info>
<authorgroup>
<author>
<firstname>Murray</firstname>
<surname>Stokely</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</sect1info>
<title>File Transfer Protocol (FTP)</title>
<indexterm><primary>FTP servers</primary></indexterm>
<sect2>
<title>Overview</title>
<para>The File Transfer Protocol (FTP) provides users with a
simple way to transfer files to and from an <acronym
role="File Transfer Protocol">FTP</acronym> server. &os;
includes <acronym role="File Transfer Protocol">FTP</acronym>
server software, <application>ftpd</application>, in the base
system. This makes setting up and administering an <acronym
role="File Transfer Protocol">FTP</acronym> server on FreeBSD
very straightforward.</para>
</sect2>
<sect2>
<title>Configuration</title>
<para>The most important configuration step is deciding which
accounts will be allowed access to the FTP server. A normal
FreeBSD system has a number of system accounts used for
various daemons, but unknown users should not be allowed to
log in with these accounts. The
<filename>/etc/ftpusers</filename> file is a list of users
disallowed any FTP access. By default, it includes the
aforementioned system accounts, but it is possible to add
specific users here that should not be allowed access to
FTP.</para>
<para>You may want to restrict the access of some users without
preventing them completely from using FTP. This can be
accomplished with the <filename>/etc/ftpchroot</filename>
file. This file lists users and groups subject to FTP access
restrictions. The &man.ftpchroot.5; manual page has all of
the details so it will not be described in detail here.</para>
<indexterm>
<primary>FTP</primary>
<secondary>anonymous</secondary>
</indexterm>
<para>If you would like to enable anonymous FTP access to your
server, then you must create a user named
<username>ftp</username> on your &os; system. Users will then
be able to log on to your FTP server with a username of
<username>ftp</username> or <username>anonymous</username> and
with any password (by convention an email address for the user
should be used as the password). The FTP server will call
&man.chroot.2; when an anonymous user logs in, to restrict
access to only the home directory of the
<username>ftp</username> user.</para>
<para>There are two text files that specify welcome messages to
be displayed to FTP clients. The contents of the file
<filename>/etc/ftpwelcome</filename> will be displayed to
users before they reach the login prompt. After a successful
login, the contents of the file
<filename>/etc/ftpmotd</filename> will be displayed. Note
that the path to this file is relative to the login environment, so the
file <filename>~ftp/etc/ftpmotd</filename> would be displayed
for anonymous users.</para>
<para>Once the FTP server has been configured properly, it must
be enabled in <filename>/etc/inetd.conf</filename>. All that
is required here is to remove the comment symbol
<quote>#</quote> from in front of the existing
<application>ftpd</application> line :</para>
<programlisting>ftp stream tcp nowait root /usr/libexec/ftpd ftpd -l</programlisting>
<para>As explained in <xref linkend="network-inetd-reread"/>,
the <application>inetd</application> configuration must be reloaded
after this configuration file is changed.</para>
<para>You can now log on to your FTP server by typing:</para>
<screen>&prompt.user; <userinput>ftp localhost</userinput></screen>
</sect2>
<sect2>
<title>Maintaining</title>
<indexterm><primary>syslog</primary></indexterm>
<indexterm><primary>log files</primary>
<secondary>FTP</secondary></indexterm>
<para>The <application>ftpd</application> daemon uses
&man.syslog.3; to log messages. By default, the system log
daemon will put messages related to FTP in the
<filename>/var/log/xferlog</filename> file. The location of
the FTP log can be modified by changing the following line in
<filename>/etc/syslog.conf</filename>:</para>
<programlisting>ftp.info /var/log/xferlog</programlisting>
<indexterm>
<primary>FTP</primary>
<secondary>anonymous</secondary>
</indexterm>
<para>Be aware of the potential problems involved with running
an anonymous FTP server. In particular, you should think
twice about allowing anonymous users to upload files. You may
find that your FTP site becomes a forum for the trade of
unlicensed commercial software or worse. If you do need to
allow anonymous FTP uploads, then you should set up the
permissions so that these files can not be read by other
anonymous users until they have been reviewed.</para>
</sect2>
</sect1>
<sect1 id="network-samba">
<sect1info>
<authorgroup>
<author>
<firstname>Murray</firstname>
<surname>Stokely</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</sect1info>
<title>File and Print Services for &microsoft.windows; clients (Samba)</title>
<indexterm><primary>Samba server</primary></indexterm>
<indexterm><primary>Microsoft Windows</primary></indexterm>
<indexterm>
<primary>file server</primary>
<secondary>Windows clients</secondary>
</indexterm>
<indexterm>
<primary>print server</primary>
<secondary>Windows clients</secondary>
</indexterm>
<sect2>
<title>Overview</title>
<para><application>Samba</application> is a popular open source
software package that provides file and print services for
&microsoft.windows; clients. Such clients can connect to and
use FreeBSD filespace as if it was a local disk drive, or
FreeBSD printers as if they were local printers.</para>
<para><application>Samba</application> software packages should
be included on your FreeBSD installation media. If you did
not install <application>Samba</application> when you first
installed FreeBSD, then you can install it from the <filename
role="package">net/samba3</filename> port or package.</para>
<!-- mention LDAP, Active Directory, WinBIND, ACL, Quotas, PAM, .. -->
</sect2>
<sect2>
<title>Configuration</title>
<para>A default <application>Samba</application> configuration
file is installed as
<filename>/usr/local/etc/smb.conf.default</filename>. This
file must be copied to
<filename>/usr/local/etc/smb.conf</filename> and customized
before <application>Samba</application> can be used.</para>
<para>The <filename>smb.conf</filename> file contains runtime
configuration information for
<application>Samba</application>, such as definitions of the
printers and <quote>file system shares</quote> that you would
like to share with &windows; clients. The
<application>Samba</application> package includes a web based
tool called <application>swat</application> which provides a
simple way of configuring the <filename>smb.conf</filename>
file.</para>
<sect3>
<title>Using the Samba Web Administration Tool (SWAT)</title>
<para>The Samba Web Administration Tool (SWAT) runs as a
daemon from <application>inetd</application>. Therefore, the
following line in <filename>/etc/inetd.conf</filename>
should be uncommented before <application>swat</application> can be
used to configure <application>Samba</application>:</para>
<programlisting>swat stream tcp nowait/400 root /usr/local/sbin/swat</programlisting>
<para>As explained in <xref linkend="network-inetd-reread"/>,
the <application>inetd</application> must be reloaded after this configuration
file is changed.</para>
<para>Once <application>swat</application> has been enabled in
<filename>inetd.conf</filename>, you can use a browser to
connect to <ulink url="http://localhost:901"></ulink>. You will
first have to log on with the system <username>root</username> account.</para>
<!-- XXX screenshots go here, loader is creating them -->
<para>Once you have successfully logged on to the main
<application>Samba</application> configuration page, you can
browse the system documentation, or begin by clicking on the
<guimenu>Globals</guimenu> tab. The <guimenu>Globals</guimenu> section corresponds to the
variables that are set in the <literal>[global]</literal>
section of
<filename>/usr/local/etc/smb.conf</filename>.</para>
</sect3>
<sect3>
<title>Global Settings</title>
<para>Whether you are using <application>swat</application> or
editing <filename>/usr/local/etc/smb.conf</filename>
directly, the first directives you are likely to encounter
when configuring <application>Samba</application>
are:</para>
<variablelist>
<varlistentry>
<term><literal>workgroup</literal></term>
<listitem>
<para>NT Domain-Name or Workgroup-Name for the computers
that will be accessing this server.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>netbios name</literal></term>
<listitem>
<indexterm><primary>NetBIOS</primary></indexterm>
<para>This sets the NetBIOS name by which a <application>Samba</application> server
is known. By default it is the same as the first
component of the host's DNS name.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>server string</literal></term>
<listitem>
<para>This sets the string that will be displayed with
the <command>net view</command> command and some other
networking tools that seek to display descriptive text
about the server.</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3>
<title>Security Settings</title>
<para>Two of the most important settings in
<filename>/usr/local/etc/smb.conf</filename> are the
security model chosen, and the backend password format for
client users. The following directives control these
options:</para>
<variablelist>
<varlistentry>
<term><literal>security</literal></term>
<listitem>
<para>The two most common options here are
<literal>security = share</literal> and <literal>security
= user</literal>. If your clients use usernames that
are the same as their usernames on your &os; machine
then you will want to use user level security. This
is the default security policy and it requires clients
to first log on before they can access shared
resources.</para>
<para>In share level security, client do not need to log
onto the server with a valid username and password
before attempting to connect to a shared resource.
This was the default security model for older versions
of <application>Samba</application>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>passdb backend</literal></term>
<listitem>
<indexterm><primary>NIS+</primary></indexterm>
<indexterm><primary>LDAP</primary></indexterm>
<indexterm><primary>SQL database</primary></indexterm>
<para><application>Samba</application> has several
different backend authentication models. You can
authenticate clients with LDAP, NIS+, a SQL database,
or a modified password file. The default
authentication method is <literal>smbpasswd</literal>,
and that is all that will be covered here.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Assuming that the default <literal>smbpasswd</literal>
backend is used, the
<filename>/usr/local/private/smbpasswd</filename> file must
be created to allow <application>Samba</application> to
authenticate clients. If you would like to give all of
your &unix; user accounts access from &windows; clients, use the
following command:</para>
<screen>&prompt.root; <userinput>grep -v "^#" /etc/passwd | make_smbpasswd &gt; /usr/local/private/smbpasswd</userinput>
&prompt.root; <userinput>chmod 600 /usr/local/private/smbpasswd</userinput></screen>
<para>Please see the <application>Samba</application>
documentation for additional information about configuration
options. With the basics outlined here, you should have
everything you need to start running
<application>Samba</application>.</para>
</sect3>
</sect2>
<sect2>
<title>Starting <application>Samba</application></title>
<para>To enable <application>Samba</application> when your
system boots, add the following line to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>samba_enable="YES"</programlisting>
<para>You can then start <application>Samba</application> at any
time by typing:</para>
<screen>&prompt.root; <userinput>/usr/local/etc/rc.d/samba.sh start</userinput>
Starting SAMBA: removing stale tdbs :
Starting nmbd.
Starting smbd.</screen>
<para><application>Samba</application> actually consists of
three separate daemons. You should see that both the
<application>nmbd</application> and <application>smbd</application> daemons
are started by the <filename>samba.sh</filename> script. If
you enabled winbind name resolution services in
<filename>smb.conf</filename>, then you will also see that
the <application>winbindd</application> daemon is started.</para>
<para>You can stop <application>Samba</application> at any time
by typing :</para>
<screen>&prompt.root; <userinput>/usr/local/etc/rc.d/samba.sh stop</userinput></screen>
<para><application>Samba</application> is a complex software
suite with functionality that allows broad integration with
&microsoft.windows; networks. For more information about
functionality beyond the basic installation described here,
please see <ulink url="http://www.samba.org"></ulink>.</para>
</sect2>
</sect1>
<sect1 id="network-ntp">
<sect1info>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Hukins</surname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</sect1info>
<title>Clock Synchronization with NTP</title>
<indexterm><primary>NTP</primary></indexterm>
<sect2>
<title>Overview</title>
<para>Over time, a computer's clock is prone to drift. The
Network Time Protocol (NTP) is one way to ensure your clock stays
accurate.</para>
<para>Many Internet services rely on, or greatly benefit from,
computers' clocks being accurate. For example, a web server
may receive requests to send a file if it has been modified since a
certain time. In a local area network environment, it is
essential that computers sharing files from the same file
server have synchronized clocks so that file timestamps stay
consistent. Services such as &man.cron.8; also rely on
an accurate system clock to run commands at the specified
times.</para>
<indexterm>
<primary>NTP</primary>
<secondary>ntpd</secondary>
</indexterm>
<para>FreeBSD ships with the &man.ntpd.8; <acronym role="Network
Time Protocol">NTP</acronym> server which can be used to query
other <acronym role="Network Time Protocol">NTP</acronym>
servers to set the clock on your machine or provide time
services to others.</para>
</sect2>
<sect2>
<title>Choosing Appropriate NTP Servers</title>
<indexterm>
<primary>NTP</primary>
<secondary>choosing servers</secondary>
</indexterm>
<para>In order to synchronize your clock, you will need to find
one or more <acronym role="Network Time
Protocol">NTP</acronym> servers to use. Your network
administrator or ISP may have set up an NTP server for this
purpose&mdash;check their documentation to see if this is the
case. There is an <ulink
url="http://ntp.isc.org/bin/view/Servers/WebHome">online
list of publicly accessible NTP servers</ulink> which you can
use to find an NTP server near to you. Make sure you are
aware of the policy for any servers you choose, and ask for
permission if required.</para>
<para>Choosing several unconnected NTP servers is a good idea in
case one of the servers you are using becomes unreachable or
its clock is unreliable. &man.ntpd.8; uses the responses it
receives from other servers intelligently&mdash;it will favor
unreliable servers less than reliable ones.</para>
</sect2>
<sect2>
<title>Configuring Your Machine</title>
<indexterm>
<primary>NTP</primary>
<secondary>configuration</secondary>
</indexterm>
<sect3>
<title>Basic Configuration</title>
<indexterm><primary>ntpdate</primary></indexterm>
<para>If you only wish to synchronize your clock when the
machine boots up, you can use &man.ntpdate.8;. This may be
appropriate for some desktop machines which are frequently
rebooted and only require infrequent synchronization, but
most machines should run &man.ntpd.8;.</para>
<para>Using &man.ntpdate.8; at boot time is also a good idea
for machines that run &man.ntpd.8;. The &man.ntpd.8;
program changes the clock gradually, whereas &man.ntpdate.8;
sets the clock, no matter how great the difference between a
machine's current clock setting and the correct time.</para>
<para>To enable &man.ntpdate.8; at boot time, add
<literal>ntpdate_enable="YES"</literal> to
<filename>/etc/rc.conf</filename>. You will also need to
specify all servers you wish to synchronize with and any
flags to be passed to &man.ntpdate.8; in
<varname>ntpdate_flags</varname>.</para>
</sect3>
<sect3>
<title>General Configuration</title>
<indexterm>
<primary>NTP</primary>
<secondary>ntp.conf</secondary>
</indexterm>
<para>NTP is configured by the
<filename>/etc/ntp.conf</filename> file in the format
described in &man.ntp.conf.5;. Here is a simple
example:</para>
<programlisting>server ntplocal.example.com prefer
server timeserver.example.org
server ntp2a.example.net
driftfile /var/db/ntp.drift</programlisting>
<para>The <literal>server</literal> option specifies which
servers are to be used, with one server listed on each line.
If a server is specified with the <literal>prefer</literal>
argument, as with <hostid
role="fqdn">ntplocal.example.com</hostid>, that server is
preferred over other servers. A response from a preferred
server will be discarded if it differs significantly from
other servers' responses, otherwise it will be used without
any consideration to other responses. The
<literal>prefer</literal> argument is normally used for NTP
servers that are known to be highly accurate, such as those
with special time monitoring hardware.</para>
<para>The <literal>driftfile</literal> option specifies which
file is used to store the system clock's frequency offset.
The &man.ntpd.8; program uses this to automatically
compensate for the clock's natural drift, allowing it to
maintain a reasonably correct setting even if it is cut off
from all external time sources for a period of time.</para>
<para>The <literal>driftfile</literal> option specifies which
file is used to store information about previous responses
from the NTP servers you are using. This file contains
internal information for NTP. It should not be modified by
any other process.</para>
</sect3>
<sect3>
<title>Controlling Access to Your Server</title>
<para>By default, your NTP server will be accessible to all
hosts on the Internet. The <literal>restrict</literal>
option in <filename>/etc/ntp.conf</filename> allows you to
control which machines can access your server.</para>
<para>If you want to deny all machines from accessing your NTP
server, add the following line to
<filename>/etc/ntp.conf</filename>:</para>
<programlisting>restrict default ignore</programlisting>
<para>If you only want to allow machines within your own
network to synchronize their clocks with your server, but
ensure they are not allowed to configure the server or used
as peers to synchronize against, add</para>
<programlisting>restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap</programlisting>
<para>instead, where <hostid role="ipaddr">192.168.1.0</hostid> is
an IP address on your network and <hostid
role="netmask">255.255.255.0</hostid> is your network's
netmask.</para>
<para><filename>/etc/ntp.conf</filename> can contain multiple
<literal>restrict</literal> options. For more details, see
the <literal>Access Control Support</literal> subsection of
&man.ntp.conf.5;.</para>
</sect3>
</sect2>
<sect2>
<title>Running the NTP Server</title>
<para>To ensure the NTP server is started at boot time, add the
line <literal>ntpd_enable="YES"</literal> to
<filename>/etc/rc.conf</filename>. If you wish to pass
additional flags to &man.ntpd.8;, edit the
<varname>ntpd_flags</varname> parameter in
<filename>/etc/rc.conf</filename>.</para>
<para>To start the server without rebooting your machine, run
<command>ntpd</command> being sure to specify any additional
parameters from <varname>ntpd_flags</varname> in
<filename>/etc/rc.conf</filename>. For example:</para>
<screen>&prompt.root; <userinput>ntpd -p /var/run/ntpd.pid</userinput></screen>
</sect2>
<sect2>
<title>Using ntpd with a Temporary Internet
Connection</title>
<para>The &man.ntpd.8; program does not need a permanent
connection to the Internet to function properly. However, if
you have a temporary connection that is configured to dial out
on demand, it is a good idea to prevent NTP traffic from
triggering a dial out or keeping the connection alive. If you
are using user PPP, you can use <literal>filter</literal>
directives in <filename>/etc/ppp/ppp.conf</filename>. For
example:</para>
<programlisting> set filter dial 0 deny udp src eq 123
# Prevent NTP traffic from initiating dial out
set filter dial 1 permit 0 0
set filter alive 0 deny udp src eq 123
# Prevent incoming NTP traffic from keeping the connection open
set filter alive 1 deny udp dst eq 123
# Prevent outgoing NTP traffic from keeping the connection open
set filter alive 2 permit 0/0 0/0</programlisting>
<para>For more details see the <literal>PACKET
FILTERING</literal> section in &man.ppp.8; and the examples in
<filename>/usr/share/examples/ppp/</filename>.</para>
<note>
<para>Some Internet access providers block low-numbered ports,
preventing NTP from functioning since replies never
reach your machine.</para>
</note>
</sect2>
<sect2>
<title>Further Information</title>
<para>Documentation for the NTP server can be found in
<filename>/usr/share/doc/ntp/</filename> in HTML
format.</para>
</sect2>
</sect1>
</chapter>
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