diff options
Diffstat (limited to 'rubbos/app/httpd-2.0.64/docs/manual/dns-caveats.html.en')
| -rw-r--r-- | rubbos/app/httpd-2.0.64/docs/manual/dns-caveats.html.en | 245 |
1 files changed, 0 insertions, 245 deletions
diff --git a/rubbos/app/httpd-2.0.64/docs/manual/dns-caveats.html.en b/rubbos/app/httpd-2.0.64/docs/manual/dns-caveats.html.en deleted file mode 100644 index 12e87973..00000000 --- a/rubbos/app/httpd-2.0.64/docs/manual/dns-caveats.html.en +++ /dev/null @@ -1,245 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!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><!-- - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - This file is generated from xml source: DO NOT EDIT - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - --> -<title>Issues Regarding DNS and Apache - Apache HTTP Server</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 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="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p> -<p class="apache">Apache HTTP Server Version 2.0</p> -<img alt="" src="./images/feather.gif" /></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 2.0</a></div><div id="page-content"><div id="preamble"><h1>Issues Regarding DNS and Apache</h1> -<div class="toplang"> -<p><span>Available Languages: </span><a href="./en/dns-caveats.html" title="English"> en </a> | -<a href="./es/dns-caveats.html" hreflang="es" rel="alternate" title="Español"> es </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 in such a way that it relies on DNS resolution - for parsing of the configuration files. If Apache requires DNS - resolution to parse the configuration files then your server - may be subject to reliability problems (ie. it might not boot), - or denial and theft of service attacks (including users able - to steal hits from other users).</p> - </div> -<div id="quickview"><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> -<li><img alt="" src="./images/down.gif" /> <a href="#appendix">Appendix: Future Directions</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> - - - <div class="example"><p><code> - <VirtualHost www.abc.dom> <br /> - ServerAdmin webgirl@abc.dom <br /> - DocumentRoot /www/abc <br /> - </VirtualHost> - </code></p></div> - - <p>In order for Apache 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 Apache must use DNS - to find the address of <code>www.abc.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 (prior to Apache version 1.2 the server - would not even boot).</p> - - <p>Suppose that <code>www.abc.dom</code> has address 10.0.0.1. - Then consider this configuration snippet:</p> - - <div class="example"><p><code> - <VirtualHost 10.0.0.1> <br /> - ServerAdmin webgirl@abc.dom <br /> - DocumentRoot /www/abc <br /> - </VirtualHost> - </code></p></div> - - <p>This time Apache 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 - (prior to Apache version 1.2 the server would not even boot). - 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 Apache should ever have to generate a full - URL for the server which includes the server name, then it will - fail to generate a valid URL.</p> - - <p>Here is a snippet that avoids both of these problems:</p> - - <div class="example"><p><code> - <VirtualHost 10.0.0.1> <br /> - ServerName www.abc.dom <br /> - ServerAdmin webgirl@abc.dom <br /> - DocumentRoot /www/abc <br /> - </VirtualHost> - </code></p></div> - </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>There are (at least) two forms that denial of service - can come in. If you are running a version of Apache prior to - version 1.2 then your server will not even boot if one of the - two DNS lookups mentioned above fails for any of your virtual - hosts. In some cases this DNS lookup may not even be under your - control; for example, if <code>abc.dom</code> is one of your - customers and they control their own DNS, they can force your - (pre-1.2) server to fail while booting simply by deleting the - <code>www.abc.dom</code> record.</p> - - <p>Another form is far more insidious. Consider this - configuration snippet:</p> - - <div class="example"><p><code> - <VirtualHost www.abc.dom> <br /> - ServerAdmin webgirl@abc.dom <br /> - DocumentRoot /www/abc <br /> - </VirtualHost> <br /> - <br /> - <VirtualHost www.def.dom> <br /> - ServerAdmin webguy@def.dom <br /> - DocumentRoot /www/def <br /> - </VirtualHost> - </code></p></div> - - <p>Suppose that you've assigned 10.0.0.1 to - <code>www.abc.dom</code> and 10.0.0.2 to - <code>www.def.dom</code>. Furthermore, suppose that - <code>def.dom</code> has control of their own DNS. With this - config you have put <code>def.dom</code> into a position where - they can steal all traffic destined to <code>abc.dom</code>. To - do so, all they have to do is set <code>www.def.dom</code> to - 10.0.0.1. Since they control their own DNS you can't stop them - from pointing the <code>www.def.dom</code> record wherever they - wish.</p> - - <p>Requests coming in to 10.0.0.1 (including all those where - users typed in URLs of the form - <code>http://www.abc.dom/whatever</code>) will all be served by - the <code>def.dom</code> virtual host. To better understand why - this happens requires a more in-depth discussion of how Apache - 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>The addition of <a href="vhosts/name-based.html">name-based - virtual host support</a> in Apache 1.1 requires Apache 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 Apache - 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 class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> -<div class="section"> -<h2><a name="appendix" id="appendix">Appendix: Future Directions</a></h2> - - - <p>The situation regarding DNS is highly undesirable. For - Apache 1.2 we've attempted to make the server at least continue - booting in the event of failed DNS, but it might not be the - best we can do. In any event, requiring the use of explicit IP - addresses in configuration files is highly undesirable in - today's Internet where renumbering is a necessity.</p> - - <p>A possible work around to the theft of service attack - described above would be to perform a reverse DNS lookup on the - IP address returned by the forward lookup and compare the two - names -- in the event of a mismatch, the virtualhost would be - disabled. This would require reverse DNS to be configured - properly (which is something that most admins are familiar with - because of the common use of "double-reverse" DNS lookups by - FTP servers and TCP wrappers).</p> - - <p>In any event, it doesn't seem possible to reliably boot a - virtual-hosted web server when DNS has failed unless IP - addresses are used. Partial solutions such as disabling - portions of the configuration might be worse than not booting - at all depending on what the webserver is supposed to - accomplish.</p> - - <p>As HTTP/1.1 is deployed and browsers and proxies start - issuing the <code>Host</code> header it will become possible to - avoid the use of IP-based virtual hosts entirely. In this case, - a webserver has no requirement to do DNS lookups during - configuration. But as of March 1997 these features have not - been deployed widely enough to be put into use on critical - webservers.</p> - </div></div> -<div class="bottomlang"> -<p><span>Available Languages: </span><a href="./en/dns-caveats.html" title="English"> en </a> | -<a href="./es/dns-caveats.html" hreflang="es" rel="alternate" title="Español"> es </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 id="footer"> -<p class="apache">Copyright 2009 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="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p></div> -</body></html>
\ No newline at end of file |