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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
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<manualpage metafile="name-based.xml.meta">
<parentdocument href="./">Virtual Hosts</parentdocument>
<title>Name-based Virtual Host Support</title>
<summary>
<p>This document describes when and how to use name-based virtual hosts.</p>
</summary>
<seealso><a href="ip-based.html">IP-based Virtual Host Support</a></seealso>
<seealso><a href="details.html">An In-Depth Discussion of Virtual Host Matching</a></seealso>
<seealso><a href="mass.html">Dynamically configured mass virtual hosting</a></seealso>
<seealso><a href="examples.html">Virtual Host examples for common setups</a></seealso>
<section id="namevip"><title>Name-based vs. IP-based Virtual Hosts</title>
<p><a href="ip-based.html">IP-based virtual hosts</a> use the IP address of the connection to
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>Name-based virtual hosting is usually simpler, since you need
only configure your DNS server to map each hostname to the correct
IP address and then configure the Apache HTTP Server to recognize
the different hostnames. Name-based virtual hosting also eases
the demand for scarce IP addresses. Therefore you should use
name-based virtual hosting unless you are using equipment
that explicitly demands IP-based hosting. Historical reasons for
IP-based virtual hosting based on client support are no longer
applicable to a general-purpose web server.</p>
<p> Name-based virtual hosting builds off of the IP-based virtual host
selection algorithm, meaning that searches for the proper server name
occur only between virtual hosts that have the best IP-based address.</p>
</section>
<section id="alg"><title>How the server selects the proper name-based virtual host</title>
<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 VirtualHost directives makes this
IP-based mapping irrelevant.</p>
<p>When a request arrives, the server will find the best (most specific) matching
<directive type="section" module="core">VirtualHost</directive> argument based on
the IP address and port used by the request. If there is more than one virtual host
containing this best-match address and port combination, Apache will further
compare the <directive module="core" >ServerName</directive> and <directive
module="core">ServerAlias</directive> directives to the server name
present in the request.</p>
<section id="defaultvhost"><title>The default name-based vhost for an IP and port combination </title>
<p> If no matching ServerName or ServerAlias is found in the set of
virtual hosts containing the most specific matching IP address and port
combination, then <strong>the first listed virtual host</strong> that
matches that will be used.</p></section>
</section>
<section id="using"><title>Using Name-based Virtual Hosts</title>
<related>
<modulelist>
<module>core</module>
</modulelist>
<directivelist>
<directive module="core">DocumentRoot</directive>
<directive module="core">ServerAlias</directive>
<directive module="core">ServerName</directive>
<directive module="core" type="section">VirtualHost</directive>
</directivelist>
</related>
<p>The first step is to create a <directive type="section"
module="core">VirtualHost</directive> block for
each different host that you would like to serve. Inside each <directive type="section"
module="core">VirtualHost</directive> block, you will need at minimum a
<directive module="core">ServerName</directive> directive to designate
which host is served and a <directive module="core">DocumentRoot</directive>
directive to show where in the filesystem the content for that host
lives.</p>
<note><title>Main host goes away</title>
<p> Any request that doesn't match an existing <directive type="section"
module="core">VirtualHost</directive> 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 <directive module="core">ServerName</directive> 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>
</note>
<p>For example, suppose that you are serving the domain
<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>
<example>
<VirtualHost *:80><br />
<indent>
# 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 />
</indent>
</VirtualHost><br />
<br />
<VirtualHost *:80><br />
<indent>ServerName other.example.com<br />
DocumentRoot /www/otherdomain<br />
</indent>
</VirtualHost><br />
</example>
<p>You can alternatively specify an explicit IP address in place of the
<code>*</code> in <directive type="section" module="core"
>VirtualHost</directive> directives. For example, you might want to do this
in order to run some name-based virtual hosts on one IP address, and either
IP-based, or another set of name-based virtual hosts on another address.</p>
<p>Many servers want to be accessible by more than one name. This is
possible with the <directive module="core">ServerAlias</directive>
directive, placed inside the <directive type="section" module="core"
>VirtualHost</directive> section. For example in the first <directive
type="section" module="core">VirtualHost</directive> block above, the
<directive module="core">ServerAlias</directive> directive indicates that
the listed names are other names which people can use to see that same
web site:</p>
<example>
ServerAlias example.com *.example.com
</example>
<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 <directive
module="core">ServerName</directive> or <code>ServerAlias</code>. You must
first have your DNS server properly configured to map those names to an IP
address associated with your server.</p>
<p>Finally, you can fine-tune the configuration of the virtual hosts
by placing other directives inside the <directive type="section"
module="core">VirtualHost</directive> containers. Most directives can be
placed in these containers and will then change the configuration only of
the relevant virtual host. To find out if a particular directive is allowed,
check the <a href="../mod/directive-dict.html#Context">Context</a> of the
directive. Configuration directives set in the <em>main server context</em>
(outside any <directive type="section" module="core">VirtualHost</directive>
container) will be used only if they are not overridden by the virtual host
settings.</p>
</section>
</manualpage>
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