network-wireless.html

这是很好的学习嵌入式LINUX的文章

different wireless modes, generally BSS (infrastructure mode, which requires an access
point), and IBSS (ad-hoc, or peer-to-peer mode). In our example, we will use the most
popular of the two, BSS mode, to talk to an access point.</p>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36465" name="AEN36465">24.3.3.3.1 Requirements</a></h4>

<p>There is only one real requirement for setting up FreeBSD as a wireless client. You
will need a wireless card that is supported by FreeBSD.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36468" name="AEN36468">24.3.3.3.2 Setting Up a Wireless
FreeBSD Client</a></h4>

<p>You will need to know a few things about the wireless network you are joining before
you start. In this example, we are joining a network that has a name of <var
class="REPLACEABLE">my_net</var>, and encryption turned off.</p>

<div class="NOTE">
<blockquote class="NOTE">
<p><b>Note:</b> In this example, we are not using encryption, which is a dangerous
situation. In the next section, you will learn how to turn on encryption, why it is
important to do so, and why some encryption technologies still do not completely protect
you.</p>
</blockquote>
</div>

<p>Make sure your card is recognized by FreeBSD:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">ifconfig -a</kbd>
wi0: flags=8843&lt;UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST&gt; mtu 1500
        inet6 fe80::202:2dff:fe2d:c938%wi0 prefixlen 64 scopeid 0x7
        inet 0.0.0.0 netmask 0xff000000 broadcast 255.255.255.255
        ether 00:09:2d:2d:c9:50
        media: IEEE 802.11 Wireless Ethernet autoselect (DS/2Mbps)
        status: no carrier
        ssid ""
        stationname "FreeBSD Wireless node"
        channel 10 authmode OPEN powersavemode OFF powersavesleep 100
        wepmode OFF weptxkey 1
</pre>

<p>Now, we can set the card to the correct settings for our network:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">ifconfig wi0 inet <var
class="REPLACEABLE">192.168.0.20</var> netmask <var
class="REPLACEABLE">255.255.255.0</var> ssid <var class="REPLACEABLE">my_net</var></kbd>
</pre>

<p>Replace <tt class="HOSTID">192.168.0.20</tt> and <tt class="HOSTID">255.255.255.0</tt>
with a valid IP address and netmask on your wired network. Remember, our access point is
bridging the data between the wireless network, and the wired network, so it will appear
to the other devices on your network that you are on the wired network just as they
are.</p>

<p>Once you have done that, you should be able to ping hosts on the wired network just as
if you were connected using a standard wired connection.</p>

<p>If you are experiencing problems with your wireless connection, check to make sure
that you are associated (connected) to the access point:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">ifconfig wi0</kbd>
</pre>

<p>should return some information, and you should see:</p>

<pre class="SCREEN">
status: associated
</pre>

<p>If it does not show <var class="LITERAL">associated</var>, then you may be out of
range of the access point, have encryption on, or possibly have a configuration
problem.</p>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN36497" name="AEN36497">24.3.3.4 Encryption</a></h3>

<p>Encryption on a wireless network is important because you no longer have the ability
to keep the network contained in a well protected area. Your wireless data will be
broadcast across your entire neighborhood, so anyone who cares to read it can. This is
where encryption comes in. By encrypting the data that is sent over the airwaves, you
make it much more difficult for any interested party to grab your data right out of the
air.</p>

<p>The two most common ways to encrypt the data between your client and the access point
are WEP, and <a href="http://www.FreeBSD.org/cgi/man.cgi?query=ipsec&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">ipsec</span>(4)</span></a>.</p>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36507" name="AEN36507">24.3.3.4.1 WEP</a></h4>

<p>WEP is an abbreviation for Wired Equivalency Protocol. WEP is an attempt to make
wireless networks as safe and secure as a wired network. Unfortunately, it has been
cracked, and is fairly trivial to break. This also means it is not something to rely on
when it comes to encrypting sensitive data.</p>

<p>It is better than nothing, so use the following to turn on WEP on your new FreeBSD
access point:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">ifconfig wi0 inet up ssid <var
class="REPLACEABLE">my_net</var> wepmode on wepkey <var
class="REPLACEABLE">0x1234567890</var> media DS/11Mbps mediaopt hostap</kbd>
</pre>

<p>And you can turn on WEP on a client with this command:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">ifconfig wi0 inet <var
class="REPLACEABLE">192.168.0.20</var> netmask <var
class="REPLACEABLE">255.255.255.0</var> ssid <var
class="REPLACEABLE">my_net</var> wepmode on wepkey <var
class="REPLACEABLE">0x1234567890</var></kbd>
</pre>

<p>Note that you should replace the <var class="REPLACEABLE">0x1234567890</var> with a
more unique key.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36528" name="AEN36528">24.3.3.4.2 IPsec</a></h4>

<p><a href="http://www.FreeBSD.org/cgi/man.cgi?query=ipsec&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">ipsec</span>(4)</span></a> is a much
more robust and powerful tool for encrypting data across a network. This is definitely
the preferred way to encrypt data over a wireless network. You can read more about <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=ipsec&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">ipsec</span>(4)</span></a> security and
how to implement it in the <a href="ipsec.html">IPsec</a> section of this handbook.</p>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN36538" name="AEN36538">24.3.3.5 Tools</a></h3>

<p>There are a small number of tools available for use in debugging and setting up your
wireless network, and here we will attempt to describe some of them and what they do.</p>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36541" name="AEN36541">24.3.3.5.1 The <b
class="APPLICATION">bsd-airtools</b> Package</a></h4>

<p>The <b class="APPLICATION">bsd-airtools</b> package is a complete toolset that
includes wireless auditing tools for WEP key cracking, access point detection, etc.</p>

<p>The <b class="APPLICATION">bsd-airtools</b> utilities can be installed from the <a
href="http://www.FreeBSD.org/cgi/url.cgi?ports/net/bsd-airtools/pkg-descr"><tt
class="FILENAME">net/bsd-airtools</tt></a> port. Information on installing ports can be
found in <a href="ports.html">Chapter 4</a> of this handbook.</p>

<p>The program <tt class="COMMAND">dstumbler</tt> is the packaged tool that allows for
access point discovery and signal to noise ratio graphing. If you are having a hard time
getting your access point up and running, <tt class="COMMAND">dstumbler</tt> may help you
get started.</p>

<p>To test your wireless network security, you may choose to use ``dweputils'' (<tt
class="COMMAND">dwepcrack</tt>, <tt class="COMMAND">dwepdump</tt> and <tt
class="COMMAND">dwepkeygen</tt>) to help you determine if WEP is the right solution to
your wireless security needs.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36558" name="AEN36558">24.3.3.5.2 The <tt
class="COMMAND">wicontrol</tt>, <tt class="COMMAND">ancontrol</tt> and <tt
class="COMMAND">raycontrol</tt> Utilities</a></h4>

<p>These are the tools you can use to control how your wireless card behaves on the
wireless network. In the examples above, we have chosen to use <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=wicontrol&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">wicontrol</span>(8)</span></a>, since
our wireless card is a <tt class="DEVICENAME">wi0</tt> interface. If you had a Cisco
wireless device, it would come up as <tt class="DEVICENAME">an0</tt>, and therefore you
would use <a href="http://www.FreeBSD.org/cgi/man.cgi?query=ancontrol&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">ancontrol</span>(8)</span></a>.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36572" name="AEN36572">24.3.3.5.3 The <tt
class="COMMAND">ifconfig</tt> Command</a></h4>

<p>The <a href="http://www.FreeBSD.org/cgi/man.cgi?query=ifconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">ifconfig</span>(8)</span></a> command
can be used to do many of the same options as <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=wicontrol&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">wicontrol</span>(8)</span></a>, however
it does lack a few options. Check <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=ifconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">ifconfig</span>(8)</span></a> for
command line parameters and options.</p>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN36587" name="AEN36587">24.3.3.6 Supported Cards</a></h3>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36589" name="AEN36589">24.3.3.6.1 Access Points</a></h4>

<p>The only cards that are currently supported for BSS (as an access point) mode are
devices based on the Prism 2, 2.5, or 3 chipsets. For a complete list, look at <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=wi&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">wi</span>(4)</span></a>.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN36595" name="AEN36595">24.3.3.6.2 Clients</a></h4>

<p>Almost all 802.11b wireless cards are currently supported under FreeBSD. Most cards
based on Prism, Spectrum24, Hermes, Aironet, and Raylink will work as a wireless network
card in IBSS (ad-hoc, peer-to-peer, and BSS) mode.</p>
</div>
</div>
</div>
</div>

<div class="NAVFOOTER">
<hr align="LEFT" width="100%" />
<table summary="Footer navigation table" width="100%" border="0" cellpadding="0"
cellspacing="0">
<tr>
<td width="33%" align="left" valign="top"><a href="network-routing.html"
accesskey="P">Prev</a></td>
<td width="34%" align="center" valign="top"><a href="index.html"
accesskey="H">Home</a></td>
<td width="33%" align="right" valign="top"><a href="network-bluetooth.html"
accesskey="N">Next</a></td>
</tr>

<tr>
<td width="33%" align="left" valign="top">Gateways and Routes</td>
<td width="34%" align="center" valign="top"><a href="advanced-networking.html"
accesskey="U">Up</a></td>
<td width="33%" align="right" valign="top">Bluetooth</td>
</tr>
</table>
</div>

<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
href="mailto:[e-mail]">[e-mail]</a>&#62;.</small></p>
</body>
</html>