<p>This document describes when and how to use name-based virtual hosts.</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#namevip">Name-based vs. IP-based Virtual Hosts</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#alg">How the server selects the proper name-based virtual host</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#using">Using Name-based Virtual Hosts</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="details.html">An In-Depth Discussion of Virtual Host Matching</a></li><li><a href="mass.html">Dynamically configured mass virtual hosting</a></li><li><a href="examples.html">Virtual Host examples for common setups</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
determine the correct virtual host to serve. Therefore you need to
have a separate IP address for each host.</p>
- <p>With name-based virtual
- hosting, the server relies on the client to report the hostname as
- part of the HTTP headers. Using this technique, many different hosts
- can share the same IP address.</p>
+ <p>With name-based virtual hosting, the server relies on the client to
+ report the hostname as part of the HTTP headers. Using this technique,
+ many different hosts can share the same IP address.</p>
<p>Name-based virtual hosting is usually simpler, since you need
only configure your DNS server to map each hostname to the correct
they are on separate IP addresses.</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="alg" id="alg">How the server selects the proper name-based virtual host</a></h2>
+
+ <p>It is important to recognize that the first step in name-based virtual
+ host resolution is IP-based resolution. Name-based virtual host
+ resolution only chooses the most appropriate name-based virtual host
+ after narrowing down the candidates to the best IP-based match. Using a wildcard (*)
+ for the IP address in all of the NameVirtualHost and VirtualHost directives makes this
+ IP-based mapping irrelevant.</p>
+
+ <p>When a request arrives, the server will first check if it is using
+ an IP address that matches exactly any <code class="directive"><a href="../mod/core.html#namevirtualhost">NameVirtualHost</a></code>. If it is, then it will look at each <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> section with a (literal) matching
+ IP address and try to find one where the <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> or <code class="directive"><a href="../mod/core.html#serveralias">ServerAlias</a></code>
+ matches the requested hostname. If it finds one, then it uses the configuration
+ for that server.</p>
+
+ <p><a name="defaultvhost" /> If no matching ServerName or ServerAlias is found in the
+ set of virtual hosts matching the NameVirtualHost directive, then
+ <strong>the first listed virtual host</strong> that matches the IP
+ address will be used.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="using" id="using">Using Name-based Virtual Hosts</a></h2>
lives.</p>
<div class="note"><h3>Main host goes away</h3>
- <p>If you are adding virtual hosts to an existing web server, you
- must also create a <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> block for the existing host. The <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> and <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> included in this virtual host should be the
- same as the global <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> and
- <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>. List this virtual
- host first in the configuration file so that it will act as the default
- host.</p>
+ <p> Any request that doesn't match an existing <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> is handled by the global
+ server configuration, regardless of the hostname or ServerName.</p>
+
+ <p> When you add a name-based virtual host to an existing server, and
+ the virtual host arguments match preexisting IP and port combinations,
+ requests will now be handled by an explicit virtual host. In this case,
+ it's usually wise to create a <a href="#defaultvhost">default virtual host</a>
+ with a <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> matching that of
+ the base server. New domains on the same interface and port, but
+ requiring separate configurations, can then be added as subsequent (non-default)
+ virtual hosts.</p>
</div>
<p>For example, suppose that you are serving the domain
- <code>www.domain.tld</code> and you wish to add the virtual host
- <code>www.otherdomain.tld</code>, which points at the same IP address.
+ <code>www.example.com</code> and you wish to add the virtual host
+ <code>other.example.com</code>, which points at the same IP address.
Then you simply add the following to <code>httpd.conf</code>:</p>
<div class="example"><p><code>
<br />
<VirtualHost *:80><br />
<span class="indent">
- ServerName www.domain.tld<br />
- ServerAlias domain.tld *.domain.tld<br />
+ # This first-listed virtual host is also the default for *:80
+ ServerName www.example.com<br />
+ ServerAlias example.com *.example.com<br />
DocumentRoot /www/domain<br />
</span>
</VirtualHost><br />
<br />
<VirtualHost *:80><br />
- <span class="indent">ServerName www.otherdomain.tld<br />
+ <span class="indent">ServerName other.example.com<br />
DocumentRoot /www/otherdomain<br />
</span>
</VirtualHost><br />
web site:</p>
<div class="example"><p><code>
- ServerAlias domain.tld *.domain.tld
+ ServerAlias example.com *.example.com
</code></p></div>
- <p>then requests for all hosts in the <code>domain.tld</code> domain will
- be served by the <code>www.domain.tld</code> virtual host. The wildcard
+ <p>then requests for all hosts in the <code>example.com</code> domain will
+ be served by the <code>www.example.com</code> virtual host. The wildcard
characters <code>*</code> and <code>?</code> can be used to match names.
Of course, you can't just make up names and place them in <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> or <code>ServerAlias</code>. You must
first have your DNS server properly configured to map those names to an IP
container) will be used only if they are not overridden by the virtual host
settings.</p>
- <p>Now when a request arrives, the server will first check if it is using
- an IP address that matches the <code class="directive"><a href="../mod/core.html#namevirtualhost">NameVirtualHost</a></code>. If it is, then it will look at each <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> section with a matching
- IP address and try to find one where the <code class="directive"><a href="../mod/core.html#servername">ServerName</a></code> or <code>ServerAlias</code> matches the requested
- hostname. If it finds one, then it uses the configuration for that server.
- If no matching virtual host is found, then <strong>the first listed virtual
- host</strong> that matches the IP address will be used.</p>
-
- <p>As a consequence, the first listed virtual host is the <em>default</em>
- virtual host. The <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> from
- the <em>main server</em> will <strong>never</strong> be used when an IP
- address matches the <code class="directive"><a href="../mod/core.html#namevirtualhost">NameVirtualHost</a></code>
- directive. If you would like to have a special configuration for requests
- that do not match any particular virtual host, simply put that configuration
- in a <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code>
- container and list it first in the configuration file.</p>
-
</div></div>
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