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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>
<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" type="section">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
  <directive module="core">NameVirtualHost</directive>.  Note that mentioning an
  IP address in a	<directive module="core">NameVirtualHost</directive> 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
  <directive type="section"	module="core">VirtualHost</directive> directive 
  should be the same as the argument to the <directive
  module="core">NameVirtualHost</directive> directive (ie, an IP address, 
  or <code>*</code> for all addresses).  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>
	If you are adding virtual hosts to an existing web server, you
	must also create a <directive type="section"	
  module="core">VirtualHost</directive> block for the existing host.
  The <directive module="core">ServerName</directive> and 
  <directive module="core">DocumentRoot</directive> included in this virtual 
  host should be the same as the global	<directive 
  module="core">ServerName</directive> and <directive 
  module="core">DocumentRoot</directive>.  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 <code>*</code> in both the <directive 
  module="core">NameVirtualHost</directive> and <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 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 <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>

	<p>Now when a request arrives, the server will first check if it is
  using an IP address that matches the <directive
  module="core">NameVirtualHost</directive>.  If it is, then it will look at
  each <directive type="section"	module="core">VirtualHost</directive>	
  section with a matching IP address and try to find one where the	
  <directive module="core">ServerName</directive> 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 <directive 
  module="core">DocumentRoot</directive> from the
	<em>main server</em> will <strong>never</strong> be used when an IP
  address matches the <directive module="core">NameVirtualHost</directive> 
  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 <directive type="section"	module="core">VirtualHost</directive> 
  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>
    <p>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.</p>
    </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>


