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From "Joshua Slive" <jos...@slive.ca>
Subject name virtual hosts
Date Thu, 11 Oct 2001 20:07:00 GMT
I don't know how I get myself started on this stuff when I have so much else
to do ;-)

Anyway, name-based.html is one of those files that was written many years
ago and has had various sentences and paragraphs changed MANY times since.
I thought it could greatly benefit from a full review, so I did a quick
rewrite.  Below is a first draft for your review.

I'd like to know:

1. Is this better than what is there now?
2. Did I miss anything important?
3. Is there any way to make is clearer?

Joshua.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <title>Name-based Virtual Hosts</title>
  </head>
  <!-- Background white, links blue (unvisited), navy (visited), red
(active) -->

  <body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
  vlink="#000080" alink="#FF0000">
    <!--#include virtual="header.html" -->

    <h1 align="CENTER">Name-based Virtual Host Support</h1>

<p>This document describes when and how to use name-based virtual hosts.</p>

<ul>
<li><a href="#namevip">Name-based vs. IP-based Virtual Hosts</a></li>
<li><a href="#using">Using Name-based Virtual Hosts</a></li>
<li><a href="#compat">Compatibility With Older Browsers</a></li>
</ul>

<p>See also: <a href="examples.html">Virtual Host examples for common
setups</a>, <a href="ip-based.html">IP-based Virtual Host Support</a>,
<a href="details.html">An In-Depth Discussion of Virtual Host
Matching</a>, and <a href="mass.html">Dynamically configured mass
virtual hosting</a>.</p>

<hr />

<h2><a name="namevip">Name-based vs. IP-based Virtual Hosts</a></h2>

    <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.  Therefore 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>

<h2><a name="using">Using Name-based Virtual Hosts</a></h2>

<table border="1">
<tr><td align="top">
<strong>Related Directives</strong><br><br>

<a href="mod/core.html#documentroot">DocumentRoot</a><br />
<a href="mod/core.html#listen">Listen</a><br />
<a href="mod/core.html#namevirtualhost">NameVirtualHost</a><br />
<a href="mod/core.html#serveralias">ServerAlias</a><br />
<a href="mod/core.html#servername">ServerName</a><br />
<a href="mod/core.html#serverpath">ServerPath</a><br />
<a href="mod/core.html#virtualhost">VirtualHost</a><br />
</td></tr></table>

<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 <a
href="../mod/core.html#namevirtualhost">NameVirtualHost</a> 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.  By default Apache listens
to all IP available addresses, but that can be changed with the
<a href="../mod/core.html#listen">Listen</a> directive.</p>

<p>The next step is to create a <a
href="../mod/core.html#virtualhost">&lt;VirtualHost&gt;</a> 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 <a
href="../mod/core.html#servername">ServerName</a> directive to
designate which host is served and a <a
href="../mod/core.html#documentroot">DocumentRoot</a> directive to
show where in the filesystem the content for that host lives.</p>

<p>For example, suppose that both <samp>www.domain.tld</samp> and
<samp>www.otherdomain.tld</samp> point at the IP address
<samp>111.22.33.44</samp>. Then you simply add the following
to <code>httpd.conf</code>:</p>

<pre>
    NameVirtualHost 111.22.33.44

    &lt;VirtualHost 111.22.33.44&gt;
    ServerName www.domain.tld
    DocumentRoot /www/domain
    &lt;/VirtualHost&gt;

    &lt;VirtualHost 111.22.33.44&gt;
    ServerName www.otherdomain.tld
    DocumentRoot /www/otherdomain
    &lt;/VirtualHost&gt;
</pre>

<p>In the simplest case, the IP address <code>111.22.44.33</code> can be
replaced by <code>*</code> to match all IP addresses for your server.</p>

<p>Many servers want to be accessible by more than one name.  This is
possible with the <a
href="../mod/core.html#serveralias"><code>ServerAlias</code></a>
directive, placed inside the &lt;VirtualHost&gt; section. For
example if you add this to the first &lt;VirtualHost&gt; block
above</p>

<blockquote><code>
ServerAlias domain.tld *.domain.tld
</code></blockquote>

<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 the IP address in the
<code>NameVirtualHost</code> directive.</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-dist.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>

<h2><a name="compat">Compatibility with Older Browsers</a></h2>

    <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>

    <p>There is a possible workaround with the <a
    href="../mod/core.html#serverpath"><code>ServerPath</code></a>
    directive, albeit a slightly cumbersome one:</p>

    <p>Example configuration:</p>
<pre>
    NameVirtualHost 111.22.33.44

    &lt;VirtualHost 111.22.33.44&gt;
    ServerName www.domain.tld
    ServerPath /domain
    DocumentRoot /web/domain
    &lt;/VirtualHost&gt;
</pre>

    <p>What does this mean? It means that a request for any URI
    beginning with "<samp>/domain</samp>" will be served from the
    virtual host <samp>www.domain.tld</samp> This means that the
    pages can be accessed as
    <code>http://www.domain.tld/domain/</code> for all clients,
    although clients sending a <samp>Host:</samp> 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
    <samp>http://www.domain.tld/domain/</samp> Then, in the virtual
    host's pages, be sure to use either purely relative links
    (<em>e.g.</em>, "<samp>file.html</samp>" or
    "<samp>../icons/image.gif</samp>" or links containing the
    prefacing <samp>/domain/</samp> (<em>e.g.</em>,
    "<samp>http://www.domain.tld/domain/misc/file.html</samp>" or
    "<samp>/domain/misc/file.html</samp>").</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>

    <p>See also: <a href="examples.html#serverpath">ServerPath
    configuration example</a></p>
    <!--#include virtual="footer.html" -->
  </body>
</html>


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