</div>
<div class="padding"></div>
+ <div class="entry">
+ <div class="title">
+ <a href="http://people.skolelinux.org/pere/blog/Automatic_proxy_configuration_with_Debian_Edu___Skolelinux.html">Automatic proxy configuration with Debian Edu / Skolelinux</a>
+ </div>
+ <div class="date">
+ 13th February 2012
+ </div>
+ <div class="body">
+ <p>New in the Squeeze version of
+<a href="http://www.skolelinux.org/">Debian Edu / Skolelinux</a> is the
+ability for clients to automatically configure their proxy settings
+based on their environment. We want all systems on the client to use
+the WPAD based proxy definition fetched from <tt>http://wpad/wpad.dat</tt>, to
+allow sites to control the proxy setting from a central place and make
+sure clients do not have hard coded proxy settings. The schools can
+change the global proxy setting by editing
+<tt>tjener:/etc/debian-edu/www/wpad.dat</tt> and the change propagate
+to all Debian Edu clients in the network.</p>
+
+<p>The problem is that some systems do not understand the WPAD system.
+In other words, how do one get from a WPAD file like this (this is a
+simple one, they can run arbitrary code):</p>
+
+<blockquote><pre>
+function FindProxyForURL(url, host)
+{
+ if (!isResolvable(host) ||
+ isPlainHostName(host) ||
+ dnsDomainIs(host, ".intern"))
+ return "DIRECT";
+ else
+ return "PROXY webcache:3128; DIRECT";
+}
+</pre></blockquote>
+
+<p>to a proxy setting in the process environment looking like this:</p>
+
+<blockquote><pre>
+http_proxy=http://webcache:3128/
+ftp_proxy=http://webcache:3128/
+</pre></blockquote>
+
+<p>To do this conversion I developed a perl script that will execute
+the javascript fragment in the WPAD file and return the proxy that
+would be used for
+<tt><a href="http://www.debian.org/">http://www.debian.org/</a></tt>,
+and insert this extracted proxy URL in <tt>/etc/environment</tt> and
+<tt>/etc/apt/apt.conf</tt>. The perl script wpad-extract work just
+fine in Squeeze, but in Wheezy the library it need to run the
+javascript code is <a href="http://bugs.debian.org/631045">no longer
+able to build</a> because the C library it depended on is now a C++
+library. I hope someone find a solution to that problem before Wheezy
+is frozen. An alternative would be for us to rewrite wpad-extract to
+use some other javascript library currently working in Wheezy, but no
+known alternative is known at the moment.</p>
+
+<p>This automatic proxy system allow the roaming workstation (aka
+laptop) setup in Debian Edu/Squeeze to use the proxy when the laptop
+is connected to the backbone network in a Debian Edu setup, and to
+automatically use any proxy present and announced using the WPAD
+feature when it is connected to other networks. And if no proxy is
+announced, direct connections will be used instead.</p>
+
+<p>Silently using a proxy announced on the network might be a privacy
+or security problem. But those controlling DHCP and DNS on a network
+could just as easily set up a transparent proxy, and force all HTTP
+and FTP connections to use a proxy anyway, so I consider that
+distinction to be academic. If you are afraid of using the wrong
+proxy, you should avoid connecting to the network in question in the
+first place. In Debian Edu, the proxy setup is updated using dhcp and
+ifupdown hooks, to make sure the configuration is updated every time
+the network setup changes.</p>
+
+The WPAD system is documented in a
+<a href="http://tools.ietf.org/html/draft-ietf-wrec-wpad-01">IETF
+draft</a> and a
+<a href="http://en.wikipedia.org/wiki/Web_Proxy_Autodiscovery_Protocol">Wikipedia
+page</a> for those that want to learn more.
+
+ </div>
+ <div class="tags">
+
+
+ Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>.
+
+
+ </div>
+ </div>
+ <div class="padding"></div>
+
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<div id="sidebar">
<li><a href="http://people.skolelinux.org/pere/blog/archive/2012/01/">January (7)</a></li>
-<li><a href="http://people.skolelinux.org/pere/blog/archive/2012/02/">February (3)</a></li>
+<li><a href="http://people.skolelinux.org/pere/blog/archive/2012/02/">February (4)</a></li>
</ul></li>
<li><a href="http://people.skolelinux.org/pere/blog/tags/debian">debian (54)</a></li>
- <li><a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu (74)</a></li>
+ <li><a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu (75)</a></li>
<li><a href="http://people.skolelinux.org/pere/blog/tags/digistan">digistan (7)</a></li>
- <li><a href="http://people.skolelinux.org/pere/blog/tags/english">english (105)</a></li>
+ <li><a href="http://people.skolelinux.org/pere/blog/tags/english">english (106)</a></li>
<li><a href="http://people.skolelinux.org/pere/blog/tags/fiksgatami">fiksgatami (13)</a></li>
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