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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 06:33:50 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 06:33:50 +0000 |
| commit | fe39ffb8b90ae4e002ed73fe98617cd590abb467 (patch) | |
| tree | b80e5956907d8aeaaffe4e4f0c068c0e6157ce8b /docs/manual/dns-caveats.html.en | |
| parent | Initial commit. (diff) | |
| download | apache2-upstream/2.4.56.tar.xz apache2-upstream/2.4.56.zip | |
Adding upstream version 2.4.56.upstream/2.4.56
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'docs/manual/dns-caveats.html.en')
| -rw-r--r-- | docs/manual/dns-caveats.html.en | 217 |
1 files changed, 217 insertions, 0 deletions
diff --git a/docs/manual/dns-caveats.html.en b/docs/manual/dns-caveats.html.en new file mode 100644 index 0000000..ac35fe4 --- /dev/null +++ b/docs/manual/dns-caveats.html.en @@ -0,0 +1,217 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head> +<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" /> +<!-- + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + This file is generated from xml source: DO NOT EDIT + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + --> +<title>Issues Regarding DNS and Apache HTTP Server - Apache HTTP Server Version 2.4</title> +<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> +<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> +<link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="./style/css/prettify.css" /> +<script src="./style/scripts/prettify.min.js" type="text/javascript"> +</script> + +<link href="./images/favicon.ico" rel="shortcut icon" /></head> +<body id="manual-page"><div id="page-header"> +<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.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> +<p class="apache">Apache HTTP Server Version 2.4</p> +<img alt="" src="./images/feather.png" /></div> +<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div> +<div id="path"> +<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 2.4</a></div><div id="page-content"><div id="preamble"><h1>Issues Regarding DNS and Apache HTTP Server</h1> +<div class="toplang"> +<p><span>Available Languages: </span><a href="./en/dns-caveats.html" title="English"> en </a> | +<a href="./fr/dns-caveats.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | +<a href="./ja/dns-caveats.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | +<a href="./ko/dns-caveats.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | +<a href="./tr/dns-caveats.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> +</div> + + <p>This page could be summarized with the statement: don't + configure Apache HTTP Server in such a way that it relies on DNS resolution + for parsing of the configuration files. If httpd requires DNS + resolution to parse the configuration files then your server + may be subject to reliability problems (ie. it might not start up), + or denial and theft of service attacks (including virtual hosts able + to steal hits from other virtual hosts).</p> + </div> +<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#example">A Simple Example</a></li> +<li><img alt="" src="./images/down.gif" /> <a href="#denial">Denial of Service</a></li> +<li><img alt="" src="./images/down.gif" /> <a href="#main">The "main server" Address</a></li> +<li><img alt="" src="./images/down.gif" /> <a href="#tips">Tips to Avoid These Problems</a></li> +</ul><h3>See also</h3><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> +<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> +<div class="section"> +<h2><a name="example" id="example">A Simple Example</a></h2> + + + <pre class="prettyprint lang-config"># This is a misconfiguration example, do not use on your server +<VirtualHost www.example.dom> + ServerAdmin webgirl@example.dom + DocumentRoot "/www/example" +</VirtualHost></pre> + + + <p>In order for the server to function properly, it absolutely needs + to have two pieces of information about each virtual host: the + <code class="directive"><a href="./mod/core.html#servername">ServerName</a></code> and at least one + IP address that the server will bind and respond to. The above + example does not include the IP address, so httpd must use DNS + to find the address of <code>www.example.dom</code>. If for some + reason DNS is not available at the time your server is parsing + its config file, then this virtual host <strong>will not be + configured</strong>. It won't be able to respond to any hits + to this virtual host.</p> + + <p>Suppose that <code>www.example.dom</code> has address 192.0.2.1. + Then consider this configuration snippet:</p> + + <pre class="prettyprint lang-config"># This is a misconfiguration example, do not use on your server +<VirtualHost 192.0.2.1> + ServerAdmin webgirl@example.dom + DocumentRoot "/www/example" +</VirtualHost></pre> + + + <p>This time httpd needs to use reverse DNS to find the + <code>ServerName</code> for this virtualhost. If that reverse + lookup fails then it will partially disable the virtualhost. + If the virtual host is name-based then it will effectively be + totally disabled, but if it is IP-based then it will mostly + work. However, if httpd should ever have to generate a full + URL for the server which includes the server name (such as when a + Redirect is issued), then it will fail to generate a valid URL.</p> + + <p>Here is a snippet that avoids both of these problems:</p> + + <pre class="prettyprint lang-config"><VirtualHost 192.0.2.1> + ServerName www.example.dom + ServerAdmin webgirl@example.dom + DocumentRoot "/www/example" +</VirtualHost></pre> + + </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> +<div class="section"> +<h2><a name="denial" id="denial">Denial of Service</a></h2> + + + <p>Consider this configuration snippet:</p> + + <pre class="prettyprint lang-config"><VirtualHost www.example1.dom> + ServerAdmin webgirl@example1.dom + DocumentRoot "/www/example1" +</VirtualHost> +<VirtualHost www.example2.dom> + ServerAdmin webguy@example2.dom + DocumentRoot "/www/example2" +</VirtualHost></pre> + + + <p>Suppose that you've assigned 192.0.2.1 to + <code>www.example1.dom</code> and 192.0.2.2 to + <code>www.example2.dom</code>. Furthermore, suppose that + <code>example1.dom</code> has control of their own DNS. With this + config you have put <code>example1.dom</code> into a position where + they can steal all traffic destined to <code>example2.dom</code>. To + do so, all they have to do is set <code>www.example1.dom</code> to + 192.0.2.2. Since they control their own DNS you can't stop them + from pointing the <code>www.example1.dom</code> record wherever they + wish.</p> + + <p>Requests coming in to 192.0.2.2 (including all those where + users typed in URLs of the form + <code>http://www.example2.dom/whatever</code>) will all be served by + the <code>example1.dom</code> virtual host. To better understand why + this happens requires a more in-depth discussion of how httpd + matches up incoming requests with the virtual host that will + serve it. A rough document describing this <a href="vhosts/details.html">is available</a>.</p> + </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> +<div class="section"> +<h2><a name="main" id="main">The "main server" Address</a></h2> + + + <p><a href="vhosts/name-based.html">Name-based + virtual host support</a> requires httpd to know + the IP address(es) of the host that <code class="program"><a href="./programs/httpd.html">httpd</a></code> + is running on. To get this address it uses either the global + <code class="directive"><a href="./mod/core.html#servername">ServerName</a></code> + (if present) or calls the C function <code>gethostname</code> + (which should return the same as typing "hostname" at the + command prompt). Then it performs a DNS lookup on this address. + At present there is no way to avoid this lookup.</p> + + <p>If you fear that this lookup might fail because your DNS + server is down then you can insert the hostname in + <code>/etc/hosts</code> (where you probably already have it so + that the machine can boot properly). Then ensure that your + machine is configured to use <code>/etc/hosts</code> in the + event that DNS fails. Depending on what OS you are using this + might be accomplished by editing <code>/etc/resolv.conf</code>, + or maybe <code>/etc/nsswitch.conf</code>.</p> + + <p>If your server doesn't have to perform DNS for any other + reason then you might be able to get away with running httpd + with the <code>HOSTRESORDER</code> environment variable set to + "local". This all depends on what OS and resolver libraries you + are using. It also affects CGIs unless you use + <code class="module"><a href="./mod/mod_env.html">mod_env</a></code> to control the environment. It's best + to consult the man pages or FAQs for your OS.</p> + </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> +<div class="section"> +<h2><a name="tips" id="tips">Tips to Avoid These Problems</a></h2> + + + <ul> + <li> + use IP addresses in + <code class="directive"><a href="./mod/core.html#virtualhost">VirtualHost</a></code> + </li> + + <li> + use IP addresses in + <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code> + </li> + + <li> + ensure all virtual hosts have an explicit + <code class="directive"><a href="./mod/core.html#servername">ServerName</a></code> + </li> + + <li>create a <code><VirtualHost _default_:*></code> + server that has no pages to serve</li> + </ul> + </div></div> +<div class="bottomlang"> +<p><span>Available Languages: </span><a href="./en/dns-caveats.html" title="English"> en </a> | +<a href="./fr/dns-caveats.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | +<a href="./ja/dns-caveats.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | +<a href="./ko/dns-caveats.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | +<a href="./tr/dns-caveats.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> +</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 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 Libera.chat, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div> +<script type="text/javascript"><!--//--><![CDATA[//><!-- +var comments_shortname = 'httpd'; +var comments_identifier = 'http://httpd.apache.org/docs/2.4/dns-caveats.html'; +(function(w, d) { + if (w.location.hostname.toLowerCase() == "httpd.apache.org") { + d.write('<div id="comments_thread"><\/div>'); + var s = d.createElement('script'); + s.type = 'text/javascript'; + s.async = true; + s.src = 'https://comments.apache.org/show_comments.lua?site=' + comments_shortname + '&page=' + comments_identifier; + (d.getElementsByTagName('head')[0] || d.getElementsByTagName('body')[0]).appendChild(s); + } + else { + d.write('<div id="comments_thread">Comments are disabled for this page at the moment.<\/div>'); + } +})(window, document); +//--><!]]></script></div><div id="footer"> +<p class="apache">Copyright 2023 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> +<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.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></div><script type="text/javascript"><!--//--><![CDATA[//><!-- +if (typeof(prettyPrint) !== 'undefined') { + prettyPrint(); +} +//--><!]]></script> +</body></html>
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