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<relativepath href=".."/>
<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>
<seealso><a href="examples.html#serverpath">ServerPath configuration example</a></seealso>

<section id="namevip"><title>Name-based vs. IP-based Virtual Hosts</title>

	<p>IP-based virtual hosts 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.  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 there is a specific reason to
	choose IP-based virtual hosting.  Some reasons why you might consider
	using IP-based virtual hosting:</p>

	<ul>
		<li>Some ancient clients are not compatible with name-based virtual
		hosting.  For name-based virtual hosting to work, the client must send
		the HTTP Host header.  This is required by HTTP/1.1, and is
		implemented by all modern HTTP/1.0 browsers as an extension.  If you
		need to support obsolete clients and still use name-based virtual
		hosting, a possible technique is discussed at the end of this
		document.</li>

		<li>Name-based virtual hosting cannot be used with SSL secure servers
		because of the nature of the SSL protocol.</li>

		<li>Some operating systems and network equipment implement bandwidth
		management techniques that cannot differentiate between hosts unless
		they are on separate IP addresses.</li>
	</ul>

</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">NameVirtualHost</directive>
	<directive module="core">ServerAlias</directive>
	<directive module="core">ServerName</directive>
	<directive module="core">ServerPath</directive>
	<directive module="core">VirtualHost</directive>
    </directivelist>
</related>

	<p>To use name-based virtual hosting, you must designate the IP
	address (and possibly port) on the server that will be accepting
	requests for the hosts.  This is configured using the <directive
	module="core">NameVirtualHost</directive> directive.
	In the normal case where any and all IP addresses on the server should
	be used, you can use <code>*</code> as the argument to
	<code>NameVirtualHost</code>.  Note that mentioning an IP address in a
	<code>NameVirtualHost</code> directive does not automatically make the
	server listen to that IP address.  See <a href="../bind.html">Setting
	which addresses and ports Apache uses</a> for more details.  In addition,
	any IP address specified here must be associated with a network interface
	on the server.</p>

	<p>The next step is to create a <directive type="section"
	module="core">VirtualHost</directive> block for
	each different host that you would like to serve.  The argument to the
	<code>&lt;VirtualHost&gt;</code> directive should be the same as the
	argument to the <code>NameVirtualHost</code> directive (ie, an IP
	address, or <code>*</code> for all addresses).  Inside each
	<code>&lt;VirtualHost&gt;</code> 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>
	If you are adding virtual hosts to an existing web server, you
	must also create a &lt;VirtualHost&gt; block for the existing host.
	The <code>ServerName</code> and <code>DocumentRoot</code> included in
	this virtual host should be the same as the global
	<code>ServerName</code> and <code>DocumentRoot</code>.  List this
	virtual host first in the configuration file so that it will act as
	the default host.
    </note>

	<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.
	Then you simply add the following to <code>httpd.conf</code>:</p>

	<example>
    NameVirtualHost *<br />
    <br />
    &lt;VirtualHost *&gt;<br />
    <indent>
    ServerName www.domain.tld<br />
    ServerAlias domain.tld *.domain.tld<br />
    DocumentRoot /www/domain<br />
    </indent>
    &lt;/VirtualHost&gt;<br />
    <br />
    &lt;VirtualHost *&gt;<br />
    <indent>ServerName www.otherdomain.tld<br />
    DocumentRoot /www/otherdomain<br />
    </indent>
    &lt;/VirtualHost&gt;<br />
	</example>

	<p>You can alternatively specify an explicit IP address in place of
	the * in both the <code>NameVirtualHost</code> and
	<code>&lt;VirtualHost&gt;</code> 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 &lt;VirtualHost&gt; section. For
	example in the first &lt;VirtualHost&gt; 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 domain.tld *.domain.tld
	</example>

	<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 characters * and ? can be used to match names.  Of course,
	you can't just make up names and place them in <code>ServerName</code>
	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
	<code>&lt;VirtualHost&gt;</code> 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 <code>&lt;VirtualHost&gt;</code> container)
	will be used only if they are not overriden 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>NameVirtualHost</code>.  If
	it is, then it will look at each <code>&lt;VirtualHost&gt;</code>
	section with a matching IP address and try to find one where the
	<code>ServerName</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>DocumentRoot</code> from the
	<em>main server</em> will <strong>never</strong> be used when an IP
	address matches the <code>NameVirtualHost</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>&lt;VirtualHost&gt;</code> container and list it first in the
	configuration file.</p>

</section>

<section id="compat"><title>Compatibility with Older Browsers</title>

    <p>As mentioned earlier, there are some clients
    who do not send the required data for the name-based virtual
    hosts to work properly. These clients will always be sent the
    pages from the first virtual host listed for that IP address
    (the <cite>primary</cite> name-based virtual host).</p>

    <note><title>How much older?</title>
    Please note that when we say older, we really do mean older. You are
    very unlikely to encounter one of these browsers in use today. All
    current versions of any browser send the <code>Host</code> header as
    required for name-based virtual hosts.
    </note>

    <p>There is a possible workaround with the <directive
    module="core">ServerPath</directive>
    directive, albeit a slightly cumbersome one:</p>

    <p>Example configuration:</p>

    <example>
    NameVirtualHost 111.22.33.44<br />
    <br />
    &lt;VirtualHost 111.22.33.44&gt;<br />
    <indent>
    ServerName www.domain.tld<br />
    ServerPath /domain<br />
    DocumentRoot /web/domain<br />
    </indent>
    &lt;/VirtualHost&gt;<br />
 	  </example>

    <p>What does this mean? It means that a request for any URI
    beginning with "<code>/domain</code>" will be served from the
    virtual host <code>www.domain.tld</code> This means that the
    pages can be accessed as
    <code>http://www.domain.tld/domain/</code> for all clients,
    although clients sending a <code>Host:</code> header can also
    access it as <code>http://www.domain.tld/</code>.</p>

    <p>In order to make this work, put a link on your primary
    virtual host's page to
    <code>http://www.domain.tld/domain/</code> Then, in the virtual
    host's pages, be sure to use either purely relative links
    (<em>e.g.</em>, "<code>file.html</code>" or
    "<code>../icons/image.gif</code>" or links containing the
    prefacing <code>/domain/</code> (<em>e.g.</em>,
    "<code>http://www.domain.tld/domain/misc/file.html</code>" or
    "<code>/domain/misc/file.html</code>").</p>

    <p>This requires a bit of discipline, but adherence to these
    guidelines will, for the most part, ensure that your pages will
    work with all browsers, new and old.</p>

</section>
</manualpage>


