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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<title>Using mod_rewrite to control access - Apache HTTP Server Version 2.5</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<body id="manual-page"><div id="page-header">
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.5</p>
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<img alt="" src="../images/feather.png" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<div id="path">
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>Using mod_rewrite to control access</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="../en/rewrite/access.html" title="English"> en </a> |
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<a href="../fr/rewrite/access.html" hreflang="fr" rel="alternate" title="Fran<61>ais"> fr </a></p>
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</div>
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<p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
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<a href="../mod/mod_rewrite.html">reference documentation</a>. It describes
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how you can use <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> to control access to
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various resources, and other related techniques.
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This includes many examples of common uses of mod_rewrite,
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including detailed descriptions of how each works.</p>
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<div class="warning">Note that many of these examples won't work unchanged in your
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particular server configuration, so it's important that you understand
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them, rather than merely cutting and pasting the examples into your
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configuration.</div>
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</div>
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<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#blocked-inline-images">Forbidding Image "Hotlinking"</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#blocking-of-robots">Blocking of Robots</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#host-deny">Denying Hosts in a Blacklist</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#referer-deflector">Referer-based Deflector</a></li>
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</ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module documentation</a></li><li><a href="intro.html">mod_rewrite introduction</a></li><li><a href="remapping.html">Redirection and remapping</a></li><li><a href="vhosts.html">Virtual hosts</a></li><li><a href="proxy.html">Proxying</a></li><li><a href="rewritemap.html">Using RewriteMap</a></li><li><a href="advanced.html">Advanced techniques</a></li><li><a href="avoid.html">When not to use mod_rewrite</a></li><li><a href="#comments_section">Comments</a></li></ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="blocked-inline-images" id="blocked-inline-images">Forbidding Image "Hotlinking"</a> <a title="Permanent link" href="#blocked-inline-images" class="permalink">¶</a></h2>
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<dl>
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<dt>Description:</dt>
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<dd>
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<p>The following technique forbids the practice of other sites
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including your images inline in their pages. This practice is
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often referred to as "hotlinking", and results in
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your bandwidth being used to serve content for someone else's
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site.</p>
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</dd>
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<dt>Solution:</dt>
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<dd>
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<p>This technique relies on the value of the
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<code>HTTP_REFERER</code> variable, which is optional. As
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such, it's possible for some people to circumvent this
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limitation. However, most users will experience the failed
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request, which should, over time, result in the image being
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removed from that other site.</p>
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<p>There are several ways that you can handle this
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situation.</p>
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<p>In this first example, we simply deny the request, if it didn't
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initiate from a page on our site. For the purpose of this example,
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we assume that our site is <code>www.example.com</code>.</p>
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<pre class="prettyprint lang-config">RewriteCond "%{HTTP_REFERER}" "!^$"
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RewriteCond "%{HTTP_REFERER}" "!www.example.com" [NC]
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RewriteRule "\.(gif|jpg|png)$" "-" [F,NC]</pre>
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<p>In this second example, instead of failing the request, we display
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an alternate image instead.</p>
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<pre class="prettyprint lang-config">RewriteCond "%{HTTP_REFERER}" "!^$"
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RewriteCond "%{HTTP_REFERER}" "!www.example.com" [NC]
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RewriteRule "\.(gif|jpg|png)$" "/images/go-away.png" [R,NC]</pre>
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<p>In the third example, we redirect the request to an image on some
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other site.</p>
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<pre class="prettyprint lang-config">RewriteCond "%{HTTP_REFERER}" "!^$"
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RewriteCond "%{HTTP_REFERER}" "!www.example.com" [NC]
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RewriteRule "\.(gif|jpg|png)$" "http://other.example.com/image.gif" [R,NC]</pre>
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<p>Of these techniques, the last two tend to be the most effective
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in getting people to stop hotlinking your images, because they will
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simply not see the image that they expected to see.</p>
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</dd>
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<dt>Discussion:</dt>
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<dd>
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<p>If all you wish to do is deny access to the resource, rather
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than redirecting that request elsewhere, this can be
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accomplished without the use of mod_rewrite:</p>
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<pre class="prettyprint lang-config">SetEnvIf Referer example\.com localreferer
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<FilesMatch "\.(jpg|png|gif)$">
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Require env localreferer
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</FilesMatch></pre>
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</dd>
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</dl>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="blocking-of-robots" id="blocking-of-robots">Blocking of Robots</a> <a title="Permanent link" href="#blocking-of-robots" class="permalink">¶</a></h2>
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<dl>
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<dt>Description:</dt>
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<dd>
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<p>
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In this recipe, we discuss how to block persistent requests from
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a particular robot, or user agent.</p>
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<p>The standard for robot exclusion defines a file,
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<code>/robots.txt</code> that specifies those portions of your
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website where you wish to exclude robots. However, some robots
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do not honor these files.
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</p>
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<p>Note that there are methods of accomplishing this which do
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not use mod_rewrite. Note also that any technique that relies on
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the clients <code>USER_AGENT</code> string can be circumvented
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very easily, since that string can be changed.</p>
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</dd>
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<dt>Solution:</dt>
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<dd>
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<p>We use a ruleset that specifies the directory to be
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protected, and the client <code>USER_AGENT</code> that
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identifies the malicious or persistent robot.</p>
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<p>In this example, we are blocking a robot called
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<code>NameOfBadRobot</code> from a location
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<code>/secret/files</code>. You may also specify an IP address
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range, if you are trying to block that user agent only from the
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particular source.</p>
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<pre class="prettyprint lang-config">RewriteCond "%{HTTP_USER_AGENT}" "^NameOfBadRobot"
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RewriteCond "%{REMOTE_ADDR}" "=123\.45\.67\.[8-9]"
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RewriteRule "^/secret/files/" "-" [F]</pre>
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</dd>
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<dt>Discussion:</dt>
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<dd>
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<p>
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Rather than using mod_rewrite for this, you can accomplish the
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same end using alternate means, as illustrated here:
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</p>
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<pre class="prettyprint lang-config">SetEnvIfNoCase User-Agent ^NameOfBadRobot goaway
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<Location "/secret/files">
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<RequireAll>
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Require all granted
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Require not env goaway
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</RequireAll>
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</Location></pre>
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<p>
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As noted above, this technique is trivial to circumvent, by simply
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modifying the <code>USER_AGENT</code> request header. If you
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are experiencing a sustained attack, you should consider blocking
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it at a higher level, such as at your firewall.
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</p>
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</dd>
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</dl>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="host-deny" id="host-deny">Denying Hosts in a Blacklist</a> <a title="Permanent link" href="#host-deny" class="permalink">¶</a></h2>
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<dl>
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<dt>Description:</dt>
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<dd>
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<p>We wish to maintain a blacklist of hosts, rather like
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<code>hosts.deny</code>, and have those hosts blocked from
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accessing our server.</p>
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</dd>
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<dt>Solution:</dt>
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<dd>
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<pre class="prettyprint lang-config">RewriteEngine on
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RewriteMap hosts-deny "txt:/path/to/hosts.deny"
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RewriteCond "${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND}" "!=NOT-FOUND" [OR]
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RewriteCond "${hosts-deny:%{REMOTE_HOST}|NOT-FOUND}" "!=NOT-FOUND"
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RewriteRule "^" "-" [F]</pre>
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<div class="example"><p><code>
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##<br />
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## hosts.deny<br />
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##<br />
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## ATTENTION! This is a map, not a list, even when we treat it as such.<br />
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## mod_rewrite parses it for key/value pairs, so at least a<br />
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## dummy value "-" must be present for each entry.<br />
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##<br />
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<br />
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193.102.180.41 -<br />
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bsdti1.sdm.de -<br />
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192.76.162.40 -<br />
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</code></p></div>
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</dd>
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<dt>Discussion:</dt>
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<dd>
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<p>
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The second RewriteCond assumes that you have HostNameLookups turned
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on, so that client IP addresses will be resolved. If that's not the
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case, you should drop the second RewriteCond, and drop the
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<code>[OR]</code> flag from the first RewriteCond.
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</p>
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</dd>
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</dl>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="referer-deflector" id="referer-deflector">Referer-based Deflector</a> <a title="Permanent link" href="#referer-deflector" class="permalink">¶</a></h2>
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<dl>
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<dt>Description:</dt>
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<dd>
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<p>Redirect requests based on the Referer from which the request
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came, with different targets per Referer.</p>
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</dd>
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<dt>Solution:</dt>
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<dd>
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<p>The following ruleset uses a map file to associate each Referer
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with a redirection target.</p>
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<pre class="prettyprint lang-config">RewriteMap deflector "txt:/path/to/deflector.map"
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RewriteCond "%{HTTP_REFERER}" !=""
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RewriteCond "${deflector:%{HTTP_REFERER}}" =-
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RewriteRule "^" "%{HTTP_REFERER}" [R,L]
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RewriteCond "%{HTTP_REFERER}" !=""
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RewriteCond "${deflector:%{HTTP_REFERER}|NOT-FOUND}" "!=NOT-FOUND"
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RewriteRule "^" "${deflector:%{HTTP_REFERER}}" [R,L]</pre>
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<p>The map file lists redirection targets for each referer, or, if
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we just wish to redirect back to where they came from, a "-" is
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placed in the map:</p>
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<pre class="prettyprint lang-config">##
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## deflector.map
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##
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http://badguys.example.com/bad/index.html -
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http://badguys.example.com/bad/index2.html -
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http://badguys.example.com/bad/index3.html http://somewhere.example.com/</pre>
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</dd>
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</dl>
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</div></div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/rewrite/access.html" title="English"> en </a> |
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<a href="../fr/rewrite/access.html" hreflang="fr" rel="alternate" title="Fran<61>ais"> fr </a></p>
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</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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