2.4.x/docs/manual/vhosts/details.html.en - httpd - Git at Google

 <?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>
 <meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type" />
 <!--
         XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
               This file is generated from xml source: DO NOT EDIT
         XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
       -->
 <title>An In-Depth Discussion of Virtual Host Matching - 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="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
 <div id="path">
 <a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.4</a> &gt; <a href="./">Virtual Hosts</a></div><div id="page-content"><div id="preamble"><h1>An In-Depth Discussion of Virtual Host Matching</h1>
 <div class="toplang">
 <p><span>Available Languages: </span><a href="../en/vhosts/details.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
 <a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
 <a href="../tr/vhosts/details.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 </div>


     <p>This document attempts to explain
     exactly what Apache HTTP Server does when deciding what virtual host to
     serve a request from.</p>

     <p>Most users should read about <a href="name-based.html#namevip">
     Name-based vs. IP-based Virtual Hosts</a> to decide which type they
     want to use, then read more about <a href="name-based.html">name-based</a>
     or <a href="ip-based.html">IP-based</a> virtualhosts, and then see
     <a href="examples.html">some examples</a>.</p>

     <p>If you want to understand all the details, then you can
     come back to this page.</p>

 </div>
 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#configparsing">Configuration File</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#hostmatching">Virtual Host Matching</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#tips">Tips</a></li>
 </ul><h3>See also</h3><ul class="seealso"><li><a href="ip-based.html">IP-based Virtual Host Support</a></li><li><a href="name-based.html">Name-based Virtual Hosts Support</a></li><li><a href="examples.html">Virtual Host examples for common setups</a></li><li><a href="mass.html">Dynamically configured mass virtual hosting</a></li><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="configparsing" id="configparsing">Configuration File</a></h2>

     <p>There is a <em>main server</em> which consists of all the
     definitions appearing outside of
     <code>&lt;VirtualHost&gt;</code> sections.</p>

     <p>There are virtual
     servers, called <em>vhosts</em>, which are defined by
     <code class="directive"><a href="../mod/core.html#virtualhost">&lt;VirtualHost&gt;</a></code>
     sections.</p>

     <p>Each <code>VirtualHost</code> directive includes one
     or more addresses and optional ports.</p>

     <p>Hostnames can be used in place of IP addresses in a virtual
     host definition, but they are resolved at startup and if any name
     resolutions fail, those virtual host definitions are ignored.
     This is, therefore, not recommended.</p>

     <p>The address can be specified as
     <code>*</code>, which will match a request if no
     other vhost has the explicit address on which the request was
     received. </p>

     <p>The address appearing in the <code>VirtualHost</code>
     directive can have an optional port. If the port is unspecified,
     it is treated as a wildcard port, which can also be indicated
     explicitly using <code>*</code>.
     The wildcard port matches any port.</p>

     <p>(Port numbers specified in the <code>VirtualHost</code> directive do
     not influence what port numbers Apache will listen on, they only control
     which <code>VirtualHost</code> will be selected to handle a request.
     Use the <code class="directive"><a href="../mod/mpm_common.html#listen">Listen</a></code> directive to
     control the addresses and ports on which the server listens.)
     </p>

     <p>Collectively the
     entire set of addresses (including multiple
     results from DNS lookups) are called the vhost's
     <em>address set</em>.</p>

     <p>Apache automatically discriminates on the
     basis of the HTTP <code>Host</code> header supplied by the client
     whenever the most specific match for an IP address and port combination
     is listed in multiple virtual hosts.</p>

     <p>The
     <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> directive
     may appear anywhere within the definition of a server. However,
     each appearance overrides the previous appearance (within that
     server).  If no <code>ServerName</code> is specified, the server
     attempts to deduce it from the server's IP address.</p>

     <p>The first name-based vhost in the configuration file for a
     given IP:port pair is significant because it is used for all
     requests received on that address and port for which no other
     vhost for that IP:port pair has a matching ServerName or
     ServerAlias.  It is also used for all SSL connections if the
     server does not support <a class="glossarylink" href="../glossary.html#servernameindication" title="see glossary">Server Name Indication</a>.</p>

     <p>The complete list of names in the <code>VirtualHost</code>
     directive are treated just like a (non wildcard) <code>ServerAlias</code>
     (but are not overridden by any <code>ServerAlias</code> statement).</p>

     <p>For every vhost various default values are set. In
     particular:</p>

     <ol>
       <li>If a vhost has no <code class="directive"><a href="../mod/core.html#serveradmin">ServerAdmin</a></code>,
       <code class="directive"><a href="../mod/core.html#timeout">Timeout</a></code>,
       <code class="directive"><a href="../mod/core.html#keepalivetimeout">KeepAliveTimeout</a></code>,
       <code class="directive"><a href="../mod/core.html#keepalive">KeepAlive</a></code>,
       <code class="directive"><a href="../mod/core.html#maxkeepaliverequests">MaxKeepAliveRequests</a></code>,
       <code class="directive"><a href="../mod/mpm_common.html#receivebuffersize">ReceiveBufferSize</a></code>,
       or <code class="directive"><a href="../mod/mpm_common.html#sendbuffersize">SendBufferSize</a></code>
       directive then the respective value is inherited from the
       main server. (That is, inherited from whatever the final
       setting of that value is in the main server.)</li>

       <li>The "lookup defaults" that define the default directory
       permissions for a vhost are merged with those of the
       main server. This includes any per-directory configuration
       information for any module.</li>

       <li>The per-server configs for each module from the
       main server are merged into the vhost server.</li>
     </ol>

     <p>Essentially, the main server is treated as "defaults" or a
     "base" on which to build each vhost. But the positioning of
     these main server definitions in the config file is largely
     irrelevant -- the entire config of the main server has been
     parsed when this final merging occurs. So even if a main server
     definition appears after a vhost definition it might affect the
     vhost definition.</p>

     <p>If the main server has no <code>ServerName</code> at this
     point, then the hostname of the machine that <code class="program"><a href="../programs/httpd.html">httpd</a></code>
     is running on is used instead. We will call the <em>main server address
     set</em> those IP addresses returned by a DNS lookup on the
     <code>ServerName</code> of the main server.</p>

     <p>For any undefined <code>ServerName</code> fields, a
     name-based vhost defaults to the address given first in the
     <code>VirtualHost</code> statement defining the vhost.</p>

     <p>Any vhost that includes the magic <code>_default_</code>
     wildcard is given the same <code>ServerName</code> as the
     main server.</p>

 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="section">
 <h2><a name="hostmatching" id="hostmatching">Virtual Host Matching</a></h2>

     <p>The server determines which vhost to use for a request as
     follows:</p>

     <h3><a name="hashtable" id="hashtable">IP address lookup</a></h3>

     <p>When the connection is first received on some address and port,
     the server looks for all the <code>VirtualHost</code> definitions
     that have the same IP address and port.</p>

     <p>If there are no exact matches for the address and port, then
     wildcard (<code>*</code>) matches are considered.</p>

     <p>If no matches are found, the request is served by the
     main server.</p>

     <p>If there are <code>VirtualHost</code> definitions for
     the IP address, the next step is to decide if we have to
     deal with an IP-based or a name-based vhost.</p>


     <h3><a name="ipbased" id="ipbased">IP-based vhost</a></h3>

     <p>If there is exactly one <code>VirtualHost</code> directive
     listing the IP address and port combination that was determined
     to be the best match, no further actions are performed and
     the request is served from the matching vhost.</p>


     <h3><a name="namebased" id="namebased">Name-based vhost</a></h3>

     <p>If there are multiple <code>VirtualHost</code> directives listing
     the IP address and port combination that was determined to be the
     best match, the "list" in the remaining steps refers to the list of vhosts
     that matched, in the order they were in the configuration file.</p>

     <p>If the connection is using SSL, the server supports <a class="glossarylink" href="../glossary.html#servernameindication" title="see glossary">Server Name Indication</a>, and
     the SSL client handshake includes the TLS extension with the
     requested hostname, then that hostname is used below just like the
     <code>Host:</code> header would be used on a non-SSL connection.
     Otherwise, the first name-based vhost whose address matched is
     used for SSL connections.  This is significant because the
     vhost determines which certificate the server will use for the
     connection.</p>

     <p>If the request contains a <code>Host:</code> header field, the
     list is searched for the first vhost with a matching
     <code>ServerName</code> or <code>ServerAlias</code>, and the
     request is served from that vhost. A <code>Host:</code> header
     field can contain a port number, but Apache always ignores it and
     matches against the real port to which the client sent the
     request.</p>

     <p>The first vhost in the config
     file with the specified IP address has the highest priority
     and catches any request to an unknown server name, or a request
     without a <code>Host:</code> header field (such as a HTTP/1.0
     request).</p>


     <h3><a name="persistent" id="persistent">Persistent connections</a></h3>

     <p>The <em>IP lookup</em> described above is only done <em>once</em> for a
     particular TCP/IP session while the <em>name lookup</em> is done on
     <em>every</em> request during a KeepAlive/persistent
     connection. In other words, a client may request pages from
     different name-based vhosts during a single persistent
     connection.</p>


     <h3><a name="absoluteURI" id="absoluteURI">Absolute URI</a></h3>

     <p>If the URI from the request is an absolute URI, and its
     hostname and port match the main server or one of the
     configured virtual hosts <em>and</em> match the address and
     port to which the client sent the request, then the
     scheme/hostname/port prefix is stripped off and the remaining
     relative URI is served by the corresponding main server or
     virtual host. If it does not match, then the URI remains
     untouched and the request is taken to be a proxy request.</p>


 <h3><a name="observations" id="observations">Observations</a></h3>

     <ul>
       <li>Name-based virtual hosting is a process applied after
       the server has selected the best matching IP-based virtual
       host.</li>

       <li>If you don't care what IP address the client has connected to, use a
       "*" as the address of every virtual host, and name-based virtual hosting
       is applied across all configured virtual hosts.</li>

       <li><code>ServerName</code> and <code>ServerAlias</code>
       checks are never performed for an IP-based vhost.</li>

       <li>Only the ordering of
       name-based vhosts for a specific address set is significant.
       The one name-based vhosts that comes first in the
       configuration file has the highest priority for its
       corresponding address set.</li>

       <li>Any port in the <code>Host:</code> header field is never used during the
       matching process. Apache always uses the real port to which
       the client sent the request.</li>

       <li>If two vhosts have an address in common, those common addresses
       act as name-based virtual hosts implicitly.  This is new behavior as of
       2.3.11.</li>

       <li>The main server is only used to serve a request if the IP
       address and port number to which the client connected
       does not match any vhost (including a
       <code>*</code> vhost). In other words, the main server
       only catches a request for an unspecified address/port
       combination (unless there is a <code>_default_</code> vhost
       which matches that port).</li>

       <li>You should never specify DNS names in
       <code>VirtualHost</code> directives because it will force
       your server to rely on DNS to boot. Furthermore it poses a
       security threat if you do not control the DNS for all the
       domains listed. There's <a href="../dns-caveats.html">more
       information</a> available on this and the next two
       topics.</li>

       <li><code>ServerName</code> should always be set for each
       vhost. Otherwise A DNS lookup is required for each
       vhost.</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="tips" id="tips">Tips</a></h2>

     <p>In addition to the tips on the <a href="../dns-caveats.html#tips">DNS Issues</a> page, here are
     some further tips:</p>

     <ul>
       <li>Place all main server definitions before any
       <code>VirtualHost</code> definitions. (This is to aid the
       readability of the configuration -- the post-config merging
       process makes it non-obvious that definitions mixed in around
       virtual hosts might affect all virtual hosts.)</li>
     </ul>

 </div></div>
 <div class="bottomlang">
 <p><span>Available Languages: </span><a href="../en/vhosts/details.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
 <a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
 <a href="../tr/vhosts/details.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</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&amp;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>
 <script type="text/javascript"><!--//--><![CDATA[//><!--
 var comments_shortname = 'httpd';
 var comments_identifier = 'http://httpd.apache.org/docs/2.4/vhosts/details.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 2016 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>
	<?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>
	<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type" />
	<!--
	XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
	This file is generated from xml source: DO NOT EDIT
	XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
	-->
	<title>An In-Depth Discussion of Virtual Host Matching - 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> > <a href="./">Virtual Hosts</a></div><div id="page-content"><div id="preamble"><h1>An In-Depth Discussion of Virtual Host Matching</h1>
	<div class="toplang">
	<p><span>Available Languages: </span><a href="../en/vhosts/details.html" title="English"> en </a> \|
	<a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français"> fr </a> \|
	<a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> \|
	<a href="../tr/vhosts/details.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
	</div>


	<p>This document attempts to explain
	exactly what Apache HTTP Server does when deciding what virtual host to
	serve a request from.</p>

	<p>Most users should read about <a href="name-based.html#namevip">
	Name-based vs. IP-based Virtual Hosts</a> to decide which type they
	want to use, then read more about <a href="name-based.html">name-based</a>
	or <a href="ip-based.html">IP-based</a> virtualhosts, and then see
	<a href="examples.html">some examples</a>.</p>

	<p>If you want to understand all the details, then you can
	come back to this page.</p>

	</div>
	<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#configparsing">Configuration File</a></li>
	<li><img alt="" src="../images/down.gif" /> <a href="#hostmatching">Virtual Host Matching</a></li>
	<li><img alt="" src="../images/down.gif" /> <a href="#tips">Tips</a></li>
	</ul><h3>See also</h3><ul class="seealso"><li><a href="ip-based.html">IP-based Virtual Host Support</a></li><li><a href="name-based.html">Name-based Virtual Hosts Support</a></li><li><a href="examples.html">Virtual Host examples for common setups</a></li><li><a href="mass.html">Dynamically configured mass virtual hosting</a></li><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="configparsing" id="configparsing">Configuration File</a></h2>

	<p>There is a <em>main server</em> which consists of all the
	definitions appearing outside of
	<code><VirtualHost></code> sections.</p>

	<p>There are virtual
	servers, called <em>vhosts</em>, which are defined by
	<code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>
	sections.</p>

	<p>Each <code>VirtualHost</code> directive includes one
	or more addresses and optional ports.</p>

	<p>Hostnames can be used in place of IP addresses in a virtual
	host definition, but they are resolved at startup and if any name
	resolutions fail, those virtual host definitions are ignored.
	This is, therefore, not recommended.</p>

	<p>The address can be specified as
	<code>*</code>, which will match a request if no
	other vhost has the explicit address on which the request was
	received. </p>

	<p>The address appearing in the <code>VirtualHost</code>
	directive can have an optional port. If the port is unspecified,
	it is treated as a wildcard port, which can also be indicated
	explicitly using <code>*</code>.
	The wildcard port matches any port.</p>

	<p>(Port numbers specified in the <code>VirtualHost</code> directive do
	not influence what port numbers Apache will listen on, they only control
	which <code>VirtualHost</code> will be selected to handle a request.
	Use the <code class="directive"><a href="../mod/mpm_common.html#listen">Listen</a></code> directive to
	control the addresses and ports on which the server listens.)
	</p>

	<p>Collectively the
	entire set of addresses (including multiple
	results from DNS lookups) are called the vhost's
	<em>address set</em>.</p>

	<p>Apache automatically discriminates on the
	basis of the HTTP <code>Host</code> header supplied by the client
	whenever the most specific match for an IP address and port combination
	is listed in multiple virtual hosts.</p>

	<p>The
	<code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> directive
	may appear anywhere within the definition of a server. However,
	each appearance overrides the previous appearance (within that
	server). If no <code>ServerName</code> is specified, the server
	attempts to deduce it from the server's IP address.</p>

	<p>The first name-based vhost in the configuration file for a
	given IP:port pair is significant because it is used for all
	requests received on that address and port for which no other
	vhost for that IP:port pair has a matching ServerName or
	ServerAlias. It is also used for all SSL connections if the
	server does not support <a class="glossarylink" href="../glossary.html#servernameindication" title="see glossary">Server Name Indication</a>.</p>

	<p>The complete list of names in the <code>VirtualHost</code>
	directive are treated just like a (non wildcard) <code>ServerAlias</code>
	(but are not overridden by any <code>ServerAlias</code> statement).</p>

	<p>For every vhost various default values are set. In
	particular:</p>

	<ol>
	<li>If a vhost has no <code class="directive"><a href="../mod/core.html#serveradmin">ServerAdmin</a></code>,
	<code class="directive"><a href="../mod/core.html#timeout">Timeout</a></code>,
	<code class="directive"><a href="../mod/core.html#keepalivetimeout">KeepAliveTimeout</a></code>,
	<code class="directive"><a href="../mod/core.html#keepalive">KeepAlive</a></code>,
	<code class="directive"><a href="../mod/core.html#maxkeepaliverequests">MaxKeepAliveRequests</a></code>,
	<code class="directive"><a href="../mod/mpm_common.html#receivebuffersize">ReceiveBufferSize</a></code>,
	or <code class="directive"><a href="../mod/mpm_common.html#sendbuffersize">SendBufferSize</a></code>
	directive then the respective value is inherited from the
	main server. (That is, inherited from whatever the final
	setting of that value is in the main server.)</li>

	<li>The "lookup defaults" that define the default directory
	permissions for a vhost are merged with those of the
	main server. This includes any per-directory configuration
	information for any module.</li>

	<li>The per-server configs for each module from the
	main server are merged into the vhost server.</li>
	</ol>

	<p>Essentially, the main server is treated as "defaults" or a
	"base" on which to build each vhost. But the positioning of
	these main server definitions in the config file is largely
	irrelevant -- the entire config of the main server has been
	parsed when this final merging occurs. So even if a main server
	definition appears after a vhost definition it might affect the
	vhost definition.</p>

	<p>If the main server has no <code>ServerName</code> at this
	point, then the hostname of the machine that <code class="program"><a href="../programs/httpd.html">httpd</a></code>
	is running on is used instead. We will call the <em>main server address
	set</em> those IP addresses returned by a DNS lookup on the
	<code>ServerName</code> of the main server.</p>

	<p>For any undefined <code>ServerName</code> fields, a
	name-based vhost defaults to the address given first in the
	<code>VirtualHost</code> statement defining the vhost.</p>

	<p>Any vhost that includes the magic <code>_default_</code>
	wildcard is given the same <code>ServerName</code> as the
	main server.</p>

	</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="section">
	<h2><a name="hostmatching" id="hostmatching">Virtual Host Matching</a></h2>

	<p>The server determines which vhost to use for a request as
	follows:</p>

	<h3><a name="hashtable" id="hashtable">IP address lookup</a></h3>

	<p>When the connection is first received on some address and port,
	the server looks for all the <code>VirtualHost</code> definitions
	that have the same IP address and port.</p>

	<p>If there are no exact matches for the address and port, then
	wildcard (<code>*</code>) matches are considered.</p>

	<p>If no matches are found, the request is served by the
	main server.</p>

	<p>If there are <code>VirtualHost</code> definitions for
	the IP address, the next step is to decide if we have to
	deal with an IP-based or a name-based vhost.</p>



	<h3><a name="ipbased" id="ipbased">IP-based vhost</a></h3>

	<p>If there is exactly one <code>VirtualHost</code> directive
	listing the IP address and port combination that was determined
	to be the best match, no further actions are performed and
	the request is served from the matching vhost.</p>



	<h3><a name="namebased" id="namebased">Name-based vhost</a></h3>

	<p>If there are multiple <code>VirtualHost</code> directives listing
	the IP address and port combination that was determined to be the
	best match, the "list" in the remaining steps refers to the list of vhosts
	that matched, in the order they were in the configuration file.</p>

	<p>If the connection is using SSL, the server supports <a class="glossarylink" href="../glossary.html#servernameindication" title="see glossary">Server Name Indication</a>, and
	the SSL client handshake includes the TLS extension with the
	requested hostname, then that hostname is used below just like the
	<code>Host:</code> header would be used on a non-SSL connection.
	Otherwise, the first name-based vhost whose address matched is
	used for SSL connections. This is significant because the
	vhost determines which certificate the server will use for the
	connection.</p>

	<p>If the request contains a <code>Host:</code> header field, the
	list is searched for the first vhost with a matching
	<code>ServerName</code> or <code>ServerAlias</code>, and the
	request is served from that vhost. A <code>Host:</code> header
	field can contain a port number, but Apache always ignores it and
	matches against the real port to which the client sent the
	request.</p>

	<p>The first vhost in the config
	file with the specified IP address has the highest priority
	and catches any request to an unknown server name, or a request
	without a <code>Host:</code> header field (such as a HTTP/1.0
	request).</p>



	<h3><a name="persistent" id="persistent">Persistent connections</a></h3>

	<p>The <em>IP lookup</em> described above is only done <em>once</em> for a
	particular TCP/IP session while the <em>name lookup</em> is done on
	<em>every</em> request during a KeepAlive/persistent
	connection. In other words, a client may request pages from
	different name-based vhosts during a single persistent
	connection.</p>



	<h3><a name="absoluteURI" id="absoluteURI">Absolute URI</a></h3>

	<p>If the URI from the request is an absolute URI, and its
	hostname and port match the main server or one of the
	configured virtual hosts <em>and</em> match the address and
	port to which the client sent the request, then the
	scheme/hostname/port prefix is stripped off and the remaining
	relative URI is served by the corresponding main server or
	virtual host. If it does not match, then the URI remains
	untouched and the request is taken to be a proxy request.</p>


	<h3><a name="observations" id="observations">Observations</a></h3>

	<ul>
	<li>Name-based virtual hosting is a process applied after
	the server has selected the best matching IP-based virtual
	host.</li>

	<li>If you don't care what IP address the client has connected to, use a
	"*" as the address of every virtual host, and name-based virtual hosting
	is applied across all configured virtual hosts.</li>

	<li><code>ServerName</code> and <code>ServerAlias</code>
	checks are never performed for an IP-based vhost.</li>

	<li>Only the ordering of
	name-based vhosts for a specific address set is significant.
	The one name-based vhosts that comes first in the
	configuration file has the highest priority for its
	corresponding address set.</li>

	<li>Any port in the <code>Host:</code> header field is never used during the
	matching process. Apache always uses the real port to which
	the client sent the request.</li>

	<li>If two vhosts have an address in common, those common addresses
	act as name-based virtual hosts implicitly. This is new behavior as of
	2.3.11.</li>

	<li>The main server is only used to serve a request if the IP
	address and port number to which the client connected
	does not match any vhost (including a
	<code>*</code> vhost). In other words, the main server
	only catches a request for an unspecified address/port
	combination (unless there is a <code>_default_</code> vhost
	which matches that port).</li>

	<li>You should never specify DNS names in
	<code>VirtualHost</code> directives because it will force
	your server to rely on DNS to boot. Furthermore it poses a
	security threat if you do not control the DNS for all the
	domains listed. There's <a href="../dns-caveats.html">more
	information</a> available on this and the next two
	topics.</li>

	<li><code>ServerName</code> should always be set for each
	vhost. Otherwise A DNS lookup is required for each
	vhost.</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="tips" id="tips">Tips</a></h2>

	<p>In addition to the tips on the <a href="../dns-caveats.html#tips">DNS Issues</a> page, here are
	some further tips:</p>

	<ul>
	<li>Place all main server definitions before any
	<code>VirtualHost</code> definitions. (This is to aid the
	readability of the configuration -- the post-config merging
	process makes it non-obvious that definitions mixed in around
	virtual hosts might affect all virtual hosts.)</li>
	</ul>

	</div></div>
	<div class="bottomlang">
	<p><span>Available Languages: </span><a href="../en/vhosts/details.html" title="English"> en </a> \|
	<a href="../fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Français"> fr </a> \|
	<a href="../ko/vhosts/details.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> \|
	<a href="../tr/vhosts/details.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 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>
	<script type="text/javascript"><!--//--><![CDATA[//><!--
	var comments_shortname = 'httpd';
	var comments_identifier = 'http://httpd.apache.org/docs/2.4/vhosts/details.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 2016 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>