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5a58787efeb02a1c3f06569d019ad81fd2efa06end<title>An In-Depth Discussion of Virtual Host Matching - Apache HTTP Server</title>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim<link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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d29d9ab4614ff992b0e8de6e2b88d52b6f1f153erbowen<body id="manual-page"><div id="page-header">
d29d9ab4614ff992b0e8de6e2b88d52b6f1f153erbowen<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="/faq/">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim<p class="apache">Apache HTTP Server Version 2.3</p>
5a58787efeb02a1c3f06569d019ad81fd2efa06end<img alt="" src="/images/feather.gif" /></div>
d229f940abfb2490dee17979e9a5ff31b7012eb5rbowen<div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="/images/left.gif" /></a></div>
3f08db06526d6901aa08c110b5bc7dde6bc39905nd<div id="path">
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.3</a> &gt; <a href="./">Virtual Hosts</a></div><div id="page-content"><div id="preamble"><h1>An In-Depth Discussion of Virtual Host Matching</h1>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim<div class="toplang">
5a58787efeb02a1c3f06569d019ad81fd2efa06end<p><span>Available Languages: </span><a href="/en/vhosts/details.html" title="English">&nbsp;en&nbsp;</a> |
3f08db06526d6901aa08c110b5bc7dde6bc39905nd<a href="/fr/vhosts/details.html" hreflang="fr" rel="alternate" title="Fran�ais">&nbsp;fr&nbsp;</a> |
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7add1372edb1ee95a2c4d1314df4c7567bda7c62jim<a href="/tr/vhosts/details.html" hreflang="tr" rel="alternate" title="T�rk�e">&nbsp;tr&nbsp;</a></p>
af84459fbf938e508fd10b01cb8d699c79083813takashi</div>
7f5b59ccc63c0c0e3e678a168f09ee6a2f51f9d0nd
f3ec420152ca921e4c1ce77782f51b53f659018dnd
f086b4b402fa9a2fefc7dda85de2a3cc1cd0a654rjung    <p>This document attempts to explain
3b3b7fc78d1f5bfc2769903375050048ff41ff26nd    exactly what Apache HTTP Server does when deciding what virtual host to
3b3b7fc78d1f5bfc2769903375050048ff41ff26nd    serve a request from.</p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    <p>Most users should read about <a href="name-based.html#namevip">
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    Name-based vs. IP-based Virtual Hosts</a> to decide which type they
5a58787efeb02a1c3f06569d019ad81fd2efa06end    want to use, then read more about <a href="name-based.html">name-based</a>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    or <a href="ip-based.html">IP-based</a> virtualhosts, and then see
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    <a href="examples.html">some examples</a>.</p>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim
709e3a21ba73b8433462959cd56c773454b34441trawick    <p>If you want to understand all the details, then you can
30471a4650391f57975f60bbb6e4a90be7b284bfhumbedooh    come back to this page.</p>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim
5a58787efeb02a1c3f06569d019ad81fd2efa06end</div>
5a58787efeb02a1c3f06569d019ad81fd2efa06end<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#configparsing">Configuration File</a></li>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele<li><img alt="" src="/images/down.gif" /> <a href="#hostmatching">Virtual Host Matching</a></li>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele<li><img alt="" src="/images/down.gif" /> <a href="#tips">Tips</a></li>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim</ul><h3>See also</h3><ul class="seealso"><li><a href="ip-based.html">IP-based Virtual Host Support</a></li><li><a href="name-based.html">Name-based Virtual Hosts Support</a></li><li><a href="examples.html">Virtual Host examples for common setups</a></li><li><a href="mass.html">Dynamically configured mass virtual hosting</a></li></ul></div>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim<div class="section">
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim<h2><a name="configparsing" id="configparsing">Configuration File</a></h2>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <p>There is a <em>main server</em> which consists of all the
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    definitions appearing outside of
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <code>&lt;VirtualHost&gt;</code> sections.</p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    <p>There are virtual
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    servers, called <em>vhosts</em>, which are defined by
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    <code class="directive"><a href="/mod/core.html#virtualhost">&lt;VirtualHost&gt;</a></code>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    sections.</p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <p>Each <code>VirtualHost</code> directive includes one
dfc515decf0e3a5a980ec4e06af4eb76d4a95440rbowen    or more addresses and optional ports.</p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <p>Hostnames can be used in place of IP addresses in a virtual
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    host definition, but they are resolved at startup and if any name
5a58787efeb02a1c3f06569d019ad81fd2efa06end    resolutions fail, those virtual host definitions are ignored.
5a58787efeb02a1c3f06569d019ad81fd2efa06end    This is, therefore, not recommended.</p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <p>If using IP-based vhosts, the address can be specified
709e3a21ba73b8433462959cd56c773454b34441trawick    as <code>_default_</code>, which will match a request if no
57d0156f7bbd9ea3a72342cf9912aba61d118702rbowen    other vhost has the explicit address on which the request was
57d0156f7bbd9ea3a72342cf9912aba61d118702rbowen    received.</p>
dfc515decf0e3a5a980ec4e06af4eb76d4a95440rbowen
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <p>If using name-based vhosts, the address can be specified as
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    <code>*</code>, which will match a request if no
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    other vhost has the explicit address on which the request was
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    received.  The corresponding <code>NameVirtualHost</code>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    directive must also use <code>*</code>.</p>
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim
5a58787efeb02a1c3f06569d019ad81fd2efa06end    <p>The address appearing in the <code>VirtualHost</code>
5a58787efeb02a1c3f06569d019ad81fd2efa06end    directive can have an optional port. If the port is unspecified,
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    it is treated as a wildcard port, which can also be indicated
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    explicitly using <code>*</code>.
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    The wildcard port matches any port.</p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <p>(Port numbers specified in the <code>VirtualHost</code> directive do
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    not influence what port numbers Apache will listen on, they only control
dfc515decf0e3a5a980ec4e06af4eb76d4a95440rbowen    which <code>VirtualHost</code> will be selected to handle a request.
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    Use the <code class="directive"><a href="/mod/core.html#listen">Listen</a></code> directive to
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    control the addresses and ports on which the server listens.)
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    </p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <p>Collectively the
dfc515decf0e3a5a980ec4e06af4eb76d4a95440rbowen    entire set of addresses (including multiple
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    results from DNS lookups) are called the vhost's
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele    <em>address set</em>.</p>
c8e71fab0ea4bc3f8cb07693d6917f6b4644fbdcerikabele
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    <p>If you want Apache to discriminate on the
87ffb6e33f3cbef3b9bb406cc2d27039fa336eaatrawick    basis of the HTTP <code>Host</code> header supplied by the client,
709e3a21ba73b8433462959cd56c773454b34441trawick    the <code>NameVirtualHost</code> directive <em>must</em> appear
709e3a21ba73b8433462959cd56c773454b34441trawick    with the exact IP address (or wildcard) and port pair used in a
709e3a21ba73b8433462959cd56c773454b34441trawick    corresponding set of <code>VirtualHost</code> directives.</p>
709e3a21ba73b8433462959cd56c773454b34441trawick
709e3a21ba73b8433462959cd56c773454b34441trawick    <p>The
709e3a21ba73b8433462959cd56c773454b34441trawick    <code class="directive"><a href="/mod/core.html#servername">ServerName</a></code> directive
709e3a21ba73b8433462959cd56c773454b34441trawick    may appear anywhere within the definition of a server. However,
709e3a21ba73b8433462959cd56c773454b34441trawick    each appearance overrides the previous appearance (within that
709e3a21ba73b8433462959cd56c773454b34441trawick    server).  If no <code>ServerName</code> is specified, the server
709e3a21ba73b8433462959cd56c773454b34441trawick    attempts to deduce it from the server's IP address.</p>
709e3a21ba73b8433462959cd56c773454b34441trawick
5a58787efeb02a1c3f06569d019ad81fd2efa06end    <p>Multiple <code>NameVirtualHost</code> directives can be used,
3b3b7fc78d1f5bfc2769903375050048ff41ff26nd    each with a set of <code>VirtualHost</code> directives, but only
7add1372edb1ee95a2c4d1314df4c7567bda7c62jim    one <code>NameVirtualHost</code> directive should be used for
af84459fbf938e508fd10b01cb8d699c79083813takashi    each specific IP:port pair.</p>
7f5b59ccc63c0c0e3e678a168f09ee6a2f51f9d0nd
f3ec420152ca921e4c1ce77782f51b53f659018dnd    <p>The first name-based vhost in the configuration file for a
f086b4b402fa9a2fefc7dda85de2a3cc1cd0a654rjung    given IP:port pair is significant because it is used for all
727872d18412fc021f03969b8641810d8896820bhumbedooh    requests received on that address and port for which no other
0d0ba3a410038e179b695446bb149cce6264e0abnd    vhost for that IP:port pair has a matching ServerName or
727872d18412fc021f03969b8641810d8896820bhumbedooh    ServerAlias.  It is also used for all SSL connections if the
cc7e1025de9ac63bd4db6fe7f71c158b2cf09fe4humbedooh    server does not support <a class="glossarylink" href="/glossary.html#servernameindication" title="see glossary">Server Name Indication</a>.</p>
0d0ba3a410038e179b695446bb149cce6264e0abnd
cc7e1025de9ac63bd4db6fe7f71c158b2cf09fe4humbedooh    <p>If there are no vhosts defined for an address in a
727872d18412fc021f03969b8641810d8896820bhumbedooh    <code>NameVirtualHost</code> directive, the
0d0ba3a410038e179b695446bb149cce6264e0abnd    <code>NameVirtualHost</code> directive is ignored at startup and an error is
0d0ba3a410038e179b695446bb149cce6264e0abnd    logged.</p>
0d0ba3a410038e179b695446bb149cce6264e0abnd
ac082aefa89416cbdc9a1836eaf3bed9698201c8humbedooh    <p>The ordering of <code>NameVirtualHost</code> and
0d0ba3a410038e179b695446bb149cce6264e0abnd    <code>VirtualHost</code> directives is not important, which
0d0ba3a410038e179b695446bb149cce6264e0abnd    makes the following two examples identical (only the order of
0d0ba3a410038e179b695446bb149cce6264e0abnd    the <code>VirtualHost</code> directives for <em>one</em>
727872d18412fc021f03969b8641810d8896820bhumbedooh    address set is important, see below):</p>
0d0ba3a410038e179b695446bb149cce6264e0abnd
0d0ba3a410038e179b695446bb149cce6264e0abnd<table><tr>
30471a4650391f57975f60bbb6e4a90be7b284bfhumbedooh<td><div class="example"><p><code>
5effc8b39fae5cd169d17f342bfc265705840014rbowen  NameVirtualHost 111.22.33.44<br />
d229f940abfb2490dee17979e9a5ff31b7012eb5rbowen  &lt;VirtualHost 111.22.33.44&gt;<br />
0d0ba3a410038e179b695446bb149cce6264e0abnd  # server A<br />
7fec19672a491661b2fe4b29f685bc7f4efa64d4nd  ...<br />
7fec19672a491661b2fe4b29f685bc7f4efa64d4nd  &lt;/VirtualHost&gt;<br />
7fec19672a491661b2fe4b29f685bc7f4efa64d4nd  &lt;VirtualHost 111.22.33.44&gt;<br />
5a58787efeb02a1c3f06569d019ad81fd2efa06end  # server B<br />
  ...<br />
  &lt;/VirtualHost&gt;<br />
  <br />
  NameVirtualHost 111.22.33.55<br />
  &lt;VirtualHost 111.22.33.55&gt;<br />
  # server C<br />
  ...<br />
  &lt;/VirtualHost&gt;<br />
  &lt;VirtualHost 111.22.33.55&gt;<br />
  # server D<br />
  ...<br />
  &lt;/VirtualHost&gt;
</code></p></div></td>
<td><div class="example"><p><code>
  &lt;VirtualHost 111.22.33.44&gt;<br />
  # server A<br />
  &lt;/VirtualHost&gt;<br />
  &lt;VirtualHost 111.22.33.55&gt;<br />
  # server C<br />
  ...<br />
  &lt;/VirtualHost&gt;<br />
  &lt;VirtualHost 111.22.33.44&gt;<br />
  # server B<br />
  ...<br />
  &lt;/VirtualHost&gt;<br />
  &lt;VirtualHost 111.22.33.55&gt;<br />
  # server D<br />
  ...<br />
  &lt;/VirtualHost&gt;<br />
  <br />
  NameVirtualHost 111.22.33.44<br />
  NameVirtualHost 111.22.33.55<br />
  <br />
</code></p></div></td>
</tr></table>


    <p>(To aid the readability of your configuration you should
    prefer the left variant.)</p>

    <p>For every vhost various default values are set. In
    particular:</p>

    <ol>
      <li>If a vhost has no <code class="directive"><a href="/mod/core.html#serveradmin">ServerAdmin</a></code>,
      <code class="directive"><a href="/mod/core.html#resourceconfig">ResourceConfig</a></code>,
      <code class="directive"><a href="/mod/core.html#accessconfig">AccessConfig</a></code>,
      <code class="directive"><a href="/mod/core.html#timeout">Timeout</a></code>,
      <code class="directive"><a href="/mod/core.html#keepalivetimeout">KeepAliveTimeout</a></code>,
      <code class="directive"><a href="/mod/core.html#keepalive">KeepAlive</a></code>,
      <code class="directive"><a href="/mod/core.html#maxkeepaliverequests">MaxKeepAliveRequests</a></code>,
      <code class="directive"><a href="/mod/core.html#receivebuffersize">ReceiveBufferSize</a></code>,
      or <code class="directive"><a href="/mod/core.html#sendbuffersize">SendBufferSize</a></code>
      directive then the respective value is inherited from the
      main server. (That is, inherited from whatever the final
      setting of that value is in the main server.)</li>

      <li>The "lookup defaults" that define the default directory
      permissions for a vhost are merged with those of the
      main server. This includes any per-directory configuration
      information for any module.</li>

      <li>The per-server configs for each module from the
      main server are merged into the vhost server.</li>
    </ol>

    <p>Essentially, the main server is treated as "defaults" or a
    "base" on which to build each vhost. But the positioning of
    these main server definitions in the config file is largely
    irrelevant -- the entire config of the main server has been
    parsed when this final merging occurs. So even if a main server
    definition appears after a vhost definition it might affect the
    vhost definition.</p>

    <p>If the main server has no <code>ServerName</code> at this
    point, then the hostname of the machine that <code class="program"><a href="/programs/httpd.html">httpd</a></code>
    is running on is used instead. We will call the <em>main server address
    set</em> those IP addresses returned by a DNS lookup on the
    <code>ServerName</code> of the main server.</p>

    <p>For any undefined <code>ServerName</code> fields, a
    name-based vhost defaults to the address given first in the
    <code>VirtualHost</code> statement defining the vhost.</p>

    <p>Any vhost that includes the magic <code>_default_</code>
    wildcard is given the same <code>ServerName</code> as the
    main server.</p>

</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="section">
<h2><a name="hostmatching" id="hostmatching">Virtual Host Matching</a></h2>

    <p>The server determines which vhost to use for a request as
    follows:</p>

    <h3><a name="hashtable" id="hashtable">IP address lookup</a></h3>

    <p>When the connection is first received on some address and port,
    the server looks for all the <code>VirtualHost</code> definitions
    that have the same IP address and port.</p>

    <p>If there are no exact matches for the address and port, then
    wildcard (<code>*</code>) matches are considered.</p>

    <p>If there are still no matches, then vhosts with IP
    address specified as <code>_default_</code> that match the
    port are considered.</p>

    <p>If no matches are found, the request is served by the
    main server.</p>

    <p>If there are <code>VirtualHost</code> definitions for
    the IP address, the next step is to decide if we have to
    deal with an IP-based or a name-based vhost.</p>


    <h3><a name="ipbased" id="ipbased">IP-based vhost</a></h3>

    <p>If there is no <code>NameVirtualHost</code> directive
    matching the vhost, no further actions are performed and
    the request is served from the first matching vhost.</p>


    <h3><a name="namebased" id="namebased">Name-based vhost</a></h3>

    <p>If the entry corresponds to a name-based vhost, the "list" in
    the remaining steps refers to the list of vhosts that matched, in
    the order they were in the configuration file.</p>

    <p>If the connection is using SSL, the server supports <a class="glossarylink" href="/glossary.html#servernameindication" title="see glossary">Server Name Indication</a>, and
    the SSL client handshake includes the TLS extension with the
    requested hostname, then that hostname is used below just like the
    <code>Host:</code> header would be used on a non-SSL connection.
    Otherwise, the first name-based vhost whose address matched is
    used for SSL connections.  This is significant because the
    vhost determines which certificate the server will use for the
    connection.</p>

    <p>If the request contains a <code>Host:</code> header field, the
    list is searched for the first vhost with a matching
    <code>ServerName</code> or <code>ServerAlias</code>, and the
    request is served from that vhost. A <code>Host:</code> header
    field can contain a port number, but Apache always ignores it and
    matches against the real port to which the client sent the
    request.</p>

    <p>The first vhost in the config
    file with the specified IP address has the highest priority
    and catches any request to an unknown server name, or a request
    without a <code>Host:</code> header field (such as a HTTP/1.0
    request).</p>


    <h3><a name="persistent" id="persistent">Persistent connections</a></h3>

    <p>The <em>IP lookup</em> described above is only done <em>once</em> for a
    particular TCP/IP session while the <em>name lookup</em> is done on
    <em>every</em> request during a KeepAlive/persistent
    connection. In other words, a client may request pages from
    different name-based vhosts during a single persistent
    connection.</p>


    <h3><a name="absoluteURI" id="absoluteURI">Absolute URI</a></h3>

    <p>If the URI from the request is an absolute URI, and its
    hostname and port match the main server or one of the
    configured virtual hosts <em>and</em> match the address and
    port to which the client sent the request, then the
    scheme/hostname/port prefix is stripped off and the remaining
    relative URI is served by the corresponding main server or
    virtual host. If it does not match, then the URI remains
    untouched and the request is taken to be a proxy request.</p>


<h3><a name="observations" id="observations">Observations</a></h3>

    <ul>
      <li>A name-based vhost can never interfere with an IP-base
      vhost and vice versa. IP-based vhosts can only be reached
      through an IP address of its own address set and never
      through any other address. The same applies to name-based
      vhosts, they can only be reached through an IP address of the
      corresponding address set which must be defined with a
      <code>NameVirtualHost</code> directive.</li>

      <li><code>ServerAlias</code>
      checks are never performed for an IP-based vhost.</li>

      <li>The order of name-/IP-based, the <code>_default_</code>
      vhost and the <code>NameVirtualHost</code> directive within
      the config file is not important. Only the ordering of
      name-based vhosts for a specific address set is significant.
      The one name-based vhosts that comes first in the
      configuration file has the highest priority for its
      corresponding address set.</li>

      <li>Any port in the <code>Host:</code> header field is never used during the
      matching process. Apache always uses the real port to which
      the client sent the request.</li>

      <li>If two IP-based vhosts have an address in common, the
      vhost appearing first in the config file is always matched.
      Such a thing might happen inadvertently. The server will give
      a warning in the error logfile when it detects this.</li>

      <li>A <code>_default_</code> vhost catches a request only if
      there is no other vhost with a matching IP address
      <em>and</em> a matching port number for the request. The
      request is only caught if the port number to which the client
      sent the request matches the port number of your
      <code>_default_</code> vhost which is your standard
      <code>Listen</code> by default. A wildcard port can be
      specified (<em>i.e.</em>, <code>_default_:*</code>) to catch
      requests to any available port. This also applies to
      <code>NameVirtualHost *</code> vhosts.  Note that this is simply an
      extension of the "best match" principle, as a specific and exact match
      is favored over a wildcard.</li>

      <li>The main server is only used to serve a request if the IP
      address and port number to which the client connected
      does not match any vhost (including a
      <code>_default_</code> vhost). In other words, the main server
      only catches a request for an unspecified address/port
      combination (unless there is a <code>_default_</code> vhost
      which matches that port).</li>

      <li>A <code>_default_</code> vhost or the main server is
      <em>never</em> matched for a request with an unknown or
      missing <code>Host:</code> header field if the client
      connected to an address (and port) which is used for
      name-based vhosts, <em>e.g.</em>, in a
      <code>NameVirtualHost</code> directive.</li>

      <li>You should never specify DNS names in
      <code>VirtualHost</code> directives because it will force
      your server to rely on DNS to boot. Furthermore it poses a
      security threat if you do not control the DNS for all the
      domains listed. There's <a href="/dns-caveats.html">more
      information</a> available on this and the next two
      topics.</li>

      <li><code>ServerName</code> should always be set for each
      vhost. Otherwise A DNS lookup is required for each
      vhost.</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="tips" id="tips">Tips</a></h2>

    <p>In addition to the tips on the <a href="/dns-caveats.html#tips">DNS Issues</a> page, here are
    some further tips:</p>

    <ul>
      <li>Place all main server definitions before any
      <code>VirtualHost</code> definitions. (This is to aid the
      readability of the configuration -- the post-config merging
      process makes it non-obvious that definitions mixed in around
      virtual hosts might affect all virtual hosts.)</li>

      <li>Group corresponding <code>NameVirtualHost</code> and
      <code>VirtualHost</code> definitions in your configuration to
      ensure better readability.</li>
    </ul>

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