network-dhcp.html

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compiled into your kernel. To do this, add <var class="LITERAL">device bpf</var> (<var
class="LITERAL">pseudo-device bpf</var> under FreeBSD&nbsp;4.X) to your kernel
configuration file, and rebuild the kernel. For more information about building kernels,
see <a href="kernelconfig.html">Chapter 8</a>.</p>

<p>The <tt class="DEVICENAME">bpf</tt> device is already part of the <tt
class="FILENAME">GENERIC</tt> kernel that is supplied with FreeBSD, so you do not need to
create a custom kernel in order to get DHCP working.</p>

<div class="NOTE">
<blockquote class="NOTE">
<p><b>Note:</b> Those who are particularly security conscious should note that <tt
class="DEVICENAME">bpf</tt> is also the device that allows packet sniffers to work
correctly (although such programs still need privileged access). <tt
class="DEVICENAME">bpf</tt> <span class="emphasis"><i class="EMPHASIS">is</i></span>
required to use DHCP, but if you are very sensitive about security, you probably should
not include <tt class="DEVICENAME">bpf</tt> in your kernel purely because you expect to
use DHCP at some point in the future.</p>
</blockquote>
</div>

<p>The next thing that you will need to do is edit the sample <tt
class="FILENAME">dhcpd.conf</tt> which was installed by the <a
href="http://www.FreeBSD.org/cgi/url.cgi?ports/net/isc-dhcp3-server/pkg-descr"><tt
class="FILENAME">net/isc-dhcp3-server</tt></a> port. By default, this will be <tt
class="FILENAME">/usr/local/etc/dhcpd.conf.sample</tt>, and you should copy this to <tt
class="FILENAME">/usr/local/etc/dhcpd.conf</tt> before proceeding to make changes.</p>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN34657" name="AEN34657">23.5.7.3 Configuring the DHCP
Server</a></h3>

<p><tt class="FILENAME">dhcpd.conf</tt> is comprised of declarations regarding subnets
and hosts, and is perhaps most easily explained using an example :</p>

<pre class="PROGRAMLISTING">
option domain-name "example.com";<a id="DOMAIN-NAME" name="DOMAIN-NAME"><img
src="./imagelib/callouts/1.png" hspace="0" vspace="0" border="0" alt="(1)" /></a>
option domain-name-servers 192.168.4.100;<a id="DOMAIN-NAME-SERVERS"
name="DOMAIN-NAME-SERVERS"><img src="./imagelib/callouts/2.png" hspace="0" vspace="0"
border="0" alt="(2)" /></a>
option subnet-mask 255.255.255.0;<a id="SUBNET-MASK" name="SUBNET-MASK"><img
src="./imagelib/callouts/3.png" hspace="0" vspace="0" border="0" alt="(3)" /></a>

default-lease-time 3600;<a id="DEFAULT-LEASE-TIME" name="DEFAULT-LEASE-TIME"><img
src="./imagelib/callouts/4.png" hspace="0" vspace="0" border="0" alt="(4)" /></a>
max-lease-time 86400;<a id="MAX-LEASE-TIME" name="MAX-LEASE-TIME"><img
src="./imagelib/callouts/5.png" hspace="0" vspace="0" border="0" alt="(5)" /></a>
ddns-update-style none;<a id="DDNS-UPDATE-STYLE" name="DDNS-UPDATE-STYLE"><img
src="./imagelib/callouts/6.png" hspace="0" vspace="0" border="0" alt="(6)" /></a>

subnet 192.168.4.0 netmask 255.255.255.0 {
  range 192.168.4.129 192.168.4.254;<a id="RANGE" name="RANGE"><img
src="./imagelib/callouts/7.png" hspace="0" vspace="0" border="0" alt="(7)" /></a>
  option routers 192.168.4.1;<a id="ROUTERS" name="ROUTERS"><img
src="./imagelib/callouts/8.png" hspace="0" vspace="0" border="0" alt="(8)" /></a>
}

host mailhost {
  hardware ethernet 02:03:04:05:06:07;<a id="HARDWARE" name="HARDWARE"><img
src="./imagelib/callouts/9.png" hspace="0" vspace="0" border="0" alt="(9)" /></a>
  fixed-address mailhost.example.com;<a id="FIXED-ADDRESS" name="FIXED-ADDRESS"><img
src="./imagelib/callouts/10.png" hspace="0" vspace="0" border="0" alt="(10)" /></a>
}
</pre>

<div class="CALLOUTLIST">
<dl compact="COMPACT">
<dt><a href="network-dhcp.html#DOMAIN-NAME"><img src="./imagelib/callouts/1.png"
hspace="0" vspace="0" border="0" alt="(1)" /></a></dt>

<dd>This option specifies the domain that will be provided to clients as the default
search domain. See <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=resolv.conf&sektion=5"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">resolv.conf</span>(5)</span></a> for
more information on what this means.</dd>

<dt><a href="network-dhcp.html#DOMAIN-NAME-SERVERS"><img src="./imagelib/callouts/2.png"
hspace="0" vspace="0" border="0" alt="(2)" /></a></dt>

<dd>This option specifies a comma separated list of DNS servers that the client should
use.</dd>

<dt><a href="network-dhcp.html#SUBNET-MASK"><img src="./imagelib/callouts/3.png"
hspace="0" vspace="0" border="0" alt="(3)" /></a></dt>

<dd>The netmask that will be provided to clients.</dd>

<dt><a href="network-dhcp.html#DEFAULT-LEASE-TIME"><img src="./imagelib/callouts/4.png"
hspace="0" vspace="0" border="0" alt="(4)" /></a></dt>

<dd>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).</dd>

<dt><a href="network-dhcp.html#MAX-LEASE-TIME"><img src="./imagelib/callouts/5.png"
hspace="0" vspace="0" border="0" alt="(5)" /></a></dt>

<dd>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 <var
class="LITERAL">max-lease-time</var> seconds.</dd>

<dt><a href="network-dhcp.html#DDNS-UPDATE-STYLE"><img src="./imagelib/callouts/6.png"
hspace="0" vspace="0" border="0" alt="(6)" /></a></dt>

<dd>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 <span
class="emphasis"><i class="EMPHASIS">required</i></span>.</dd>

<dt><a href="network-dhcp.html#RANGE"><img src="./imagelib/callouts/7.png" hspace="0"
vspace="0" border="0" alt="(7)" /></a></dt>

<dd>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.</dd>

<dt><a href="network-dhcp.html#ROUTERS"><img src="./imagelib/callouts/8.png" hspace="0"
vspace="0" border="0" alt="(8)" /></a></dt>

<dd>Declares the default gateway that will be provided to clients.</dd>

<dt><a href="network-dhcp.html#HARDWARE"><img src="./imagelib/callouts/9.png" hspace="0"
vspace="0" border="0" alt="(9)" /></a></dt>

<dd>The hardware MAC address of a host (so that the DHCP server can recognize a host when
it makes a request).</dd>

<dt><a href="network-dhcp.html#FIXED-ADDRESS"><img src="./imagelib/callouts/10.png"
hspace="0" vspace="0" border="0" alt="(10)" /></a></dt>

<dd>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.</dd>
</dl>
</div>

<p>Once you have finished writing your <tt class="FILENAME">dhcpd.conf</tt>, you can
proceed to start the server by issuing the following command:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd
class="USERINPUT">/usr/local/etc/rc.d/isc-dhcpd.sh start</kbd>
</pre>

<p>Should you need to make changes to the configuration of your server in the future, it
is important to note that sending a <var class="LITERAL">SIGHUP</var> signal to <b
class="APPLICATION">dhcpd</b> does <span class="emphasis"><i
class="EMPHASIS">not</i></span> result in the configuration being reloaded, as it does
with most daemons. You will need to send a <var class="LITERAL">SIGTERM</var> signal to
stop the process, and then restart it using the command above.</p>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN34711" name="AEN34711">23.5.7.4 Files</a></h3>

<ul>
<li>
<p><tt class="FILENAME">/usr/local/sbin/dhcpd</tt></p>

<p><b class="APPLICATION">dhcpd</b> is statically linked and resides in <tt
class="FILENAME">/usr/local/sbin</tt>. The <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=dhcpd&sektion=8&manpath=FreeBSD+Ports"><span
 class="CITEREFENTRY"><span class="REFENTRYTITLE">dhcpd</span>(8)</span></a> manual page
installed with the port gives more information about <b
class="APPLICATION">dhcpd</b>.</p>
</li>

<li>
<p><tt class="FILENAME">/usr/local/etc/dhcpd.conf</tt></p>

<p><b class="APPLICATION">dhcpd</b> requires a configuration file, <tt
class="FILENAME">/usr/local/etc/dhcpd.conf</tt> 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 <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=dhcpd.conf&sektion=5&manpath=FreeBSD+Ports">
<span class="CITEREFENTRY"><span class="REFENTRYTITLE">dhcpd.conf</span>(5)</span></a>
manual page installed by the port.</p>
</li>

<li>
<p><tt class="FILENAME">/var/db/dhcpd.leases</tt></p>

<p>The DHCP server keeps a database of leases it has issued in this file, which is
written as a log. The manual page <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=dhcpd.leases&sektion=5&manpath=FreeBSD+Ports">
<span class="CITEREFENTRY"><span class="REFENTRYTITLE">dhcpd.leases</span>(5)</span></a>,
installed by the port gives a slightly longer description.</p>
</li>

<li>
<p><tt class="FILENAME">/usr/local/sbin/dhcrelay</tt></p>

<p><b class="APPLICATION">dhcrelay</b> 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 <a
href="http://www.FreeBSD.org/cgi/url.cgi?ports/net/isc-dhcp3-relay/pkg-descr"><tt
class="FILENAME">net/isc-dhcp3-relay</tt></a> port. The <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=dhcrelay&sektion=8&manpath=FreeBSD+Ports"><span
 class="CITEREFENTRY"><span class="REFENTRYTITLE">dhcrelay</span>(8)</span></a> manual
page provided with the port contains more detail.</p>
</li>
</ul>
</div>
</div>
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<p align="center"><small>This, and other documents, can be downloaded from <a
href="ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/">ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/</a>.</small></p>

<p align="center"><small>For questions about FreeBSD, read the <a
href="http://www.FreeBSD.org/docs.html">documentation</a> before contacting &#60;<a
href="mailto:[e-mail]">[e-mail]</a>&#62;.<br />
For questions about this documentation, e-mail &#60;<a
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