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268 lines
13 KiB
XML
268 lines
13 KiB
XML
<?xml version='1.0' encoding='UTF-8' ?>
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<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<!--
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Copyright 2002-2004 The Apache Software Foundation
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<manualpage metafile="name-based.xml.meta">
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<parentdocument href="./">Virtual Hosts</parentdocument>
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<title>Name-based Virtual Host Support</title>
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<summary>
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<p>This document describes when and how to use name-based virtual hosts.</p>
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</summary>
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<seealso><a href="ip-based.html">IP-based Virtual Host Support</a></seealso>
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<seealso><a href="details.html">An In-Depth Discussion of Virtual Host Matching</a></seealso>
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<seealso><a href="mass.html">Dynamically configured mass virtual hosting</a></seealso>
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<seealso><a href="examples.html">Virtual Host examples for common setups</a></seealso>
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<seealso><a href="examples.html#serverpath">ServerPath configuration example</a></seealso>
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<section id="namevip"><title>Name-based vs. IP-based Virtual Hosts</title>
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<p>IP-based virtual hosts use the IP address of the connection to
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determine the correct virtual host to serve. Therefore you need to
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have a separate IP address for each host. With name-based virtual
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hosting, the server relies on the client to report the hostname as
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part of the HTTP headers. Using this technique, many different hosts
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can share the same IP address.</p>
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<p>Name-based virtual hosting is usually simpler, since you need
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only configure your DNS server to map each hostname to the correct
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IP address and then configure the Apache HTTP Server to recognize
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the different hostnames. Name-based virtual hosting also eases
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the demand for scarce IP addresses. Therefore you should use
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name-based virtual hosting unless there is a specific reason to
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choose IP-based virtual hosting. Some reasons why you might consider
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using IP-based virtual hosting:</p>
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<ul>
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<li>Some ancient clients are not compatible with name-based virtual
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hosting. For name-based virtual hosting to work, the client must send
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the HTTP Host header. This is required by HTTP/1.1, and is
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implemented by all modern HTTP/1.0 browsers as an extension. If you
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need to support obsolete clients and still use name-based virtual
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hosting, a possible technique is discussed at the end of this
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document.</li>
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<li>Name-based virtual hosting cannot be used with SSL secure servers
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because of the nature of the SSL protocol.</li>
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<li>Some operating systems and network equipment implement bandwidth
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management techniques that cannot differentiate between hosts unless
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they are on separate IP addresses.</li>
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</ul>
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</section>
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<section id="using"><title>Using Name-based Virtual Hosts</title>
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<related>
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<modulelist>
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<module>core</module>
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</modulelist>
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<directivelist>
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<directive module="core">DocumentRoot</directive>
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<directive module="core">NameVirtualHost</directive>
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<directive module="core">ServerAlias</directive>
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<directive module="core">ServerName</directive>
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<directive module="core">ServerPath</directive>
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<directive module="core" type="section">VirtualHost</directive>
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</directivelist>
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</related>
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<p>To use name-based virtual hosting, you must designate the IP
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address (and possibly port) on the server that will be accepting
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requests for the hosts. This is configured using the <directive
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module="core">NameVirtualHost</directive> directive.
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In the normal case where any and all IP addresses on the server should
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be used, you can use <code>*</code> as the argument to <directive
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module="core">NameVirtualHost</directive>. If you're planning to use
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multiple ports (e.g. running SSL) you should add a Port to the argument,
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such as <code>*:80</code>. Note that mentioning an IP address in a
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<directive module="core">NameVirtualHost</directive> directive does not
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automatically make the server listen to that IP address. See
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<a href="../bind.html">Setting which addresses and ports Apache uses</a>
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for more details. In addition, any IP address specified here must be
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associated with a network interface on the server.</p>
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<p>The next step is to create a <directive type="section"
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module="core">VirtualHost</directive> block for
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each different host that you would like to serve. The argument to the
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<directive type="section" module="core">VirtualHost</directive> directive
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should be the same as the argument to the <directive
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module="core">NameVirtualHost</directive> directive (ie, an IP address,
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or <code>*</code> for all addresses). Inside each <directive type="section"
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module="core">VirtualHost</directive> block, you will need at minimum a
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<directive module="core">ServerName</directive> directive to designate
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which host is served and a <directive module="core">DocumentRoot</directive>
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directive to show where in the filesystem the content for that host
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lives.</p>
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<note><title>Main host goes away</title>
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<p>If you are adding virtual hosts to an existing web server, you
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must also create a <directive type="section" module="core"
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>VirtualHost</directive> block for the existing host. The <directive
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module="core">ServerName</directive> and <directive module="core"
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>DocumentRoot</directive> included in this virtual host should be the
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same as the global <directive module="core">ServerName</directive> and
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<directive module="core">DocumentRoot</directive>. List this virtual
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host first in the configuration file so that it will act as the default
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host.</p>
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</note>
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<p>For example, suppose that you are serving the domain
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<code>www.domain.tld</code> and you wish to add the virtual host
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<code>www.otherdomain.tld</code>, which points at the same IP address.
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Then you simply add the following to <code>httpd.conf</code>:</p>
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<example>
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NameVirtualHost *:80<br />
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<br />
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<VirtualHost *:80><br />
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<indent>
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ServerName www.domain.tld<br />
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ServerAlias domain.tld *.domain.tld<br />
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DocumentRoot /www/domain<br />
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</indent>
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</VirtualHost><br />
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<br />
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<VirtualHost *:80><br />
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<indent>ServerName www.otherdomain.tld<br />
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DocumentRoot /www/otherdomain<br />
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</indent>
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</VirtualHost><br />
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</example>
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<p>You can alternatively specify an explicit IP address in place of the
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<code>*</code> in both the <directive module="core"
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>NameVirtualHost</directive> and <directive type="section" module="core"
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>VirtualHost</directive> directives. For example, you might want to do this
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in order to run some name-based virtual hosts on one IP address, and either
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IP-based, or another set of name-based virtual hosts on another address.</p>
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<p>Many servers want to be accessible by more than one name. This is
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possible with the <directive module="core">ServerAlias</directive>
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directive, placed inside the <directive type="section" module="core"
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>VirtualHost</directive> section. For example in the first <directive
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type="section" module="core">VirtualHost</directive> block above, the
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<directive module="core">ServerAlias</directive> directive indicates that
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the listed names are other names which people can use to see that same
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web site:</p>
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<example>
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ServerAlias domain.tld *.domain.tld
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</example>
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<p>then requests for all hosts in the <code>domain.tld</code> domain will
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be served by the <code>www.domain.tld</code> virtual host. The wildcard
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characters <code>*</code> and <code>?</code> can be used to match names.
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Of course, you can't just make up names and place them in <directive
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module="core">ServerName</directive> or <code>ServerAlias</code>. You must
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first have your DNS server properly configured to map those names to an IP
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address associated with your server.</p>
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<p>Finally, you can fine-tune the configuration of the virtual hosts
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by placing other directives inside the <directive type="section"
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module="core">VirtualHost</directive> containers. Most directives can be
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placed in these containers and will then change the configuration only of
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the relevant virtual host. To find out if a particular directive is allowed,
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check the <a href="../mod/directive-dict.html#Context">Context</a> of the
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directive. Configuration directives set in the <em>main server context</em>
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(outside any <directive type="section" module="core">VirtualHost</directive>
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container) will be used only if they are not overridden by the virtual host
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settings.</p>
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<p>Now when a request arrives, the server will first check if it is using
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an IP address that matches the <directive module="core"
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>NameVirtualHost</directive>. If it is, then it will look at each <directive
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type="section" module="core">VirtualHost</directive> section with a matching
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IP address and try to find one where the <directive module="core"
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>ServerName</directive> or <code>ServerAlias</code> matches the requested
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hostname. If it finds one, then it uses the configuration for that server.
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If no matching virtual host is found, then <strong>the first listed virtual
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host</strong> that matches the IP address will be used.</p>
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<p>As a consequence, the first listed virtual host is the <em>default</em>
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virtual host. The <directive module="core">DocumentRoot</directive> from
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the <em>main server</em> will <strong>never</strong> be used when an IP
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address matches the <directive module="core">NameVirtualHost</directive>
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directive. If you would like to have a special configuration for requests
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that do not match any particular virtual host, simply put that configuration
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in a <directive type="section" module="core">VirtualHost</directive>
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container and list it first in the configuration file.</p>
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</section>
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<section id="compat"><title>Compatibility with Older Browsers</title>
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<p>As mentioned earlier, there are some clients
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who do not send the required data for the name-based virtual
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hosts to work properly. These clients will always be sent the
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pages from the first virtual host listed for that IP address
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(the <cite>primary</cite> name-based virtual host).</p>
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<note><title>How much older?</title>
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<p>Please note that when we say older, we really do mean older. You are
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very unlikely to encounter one of these browsers in use today. All
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current versions of any browser send the <code>Host</code> header as
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required for name-based virtual hosts.</p>
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</note>
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<p>There is a possible workaround with the <directive
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module="core">ServerPath</directive>
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directive, albeit a slightly cumbersome one:</p>
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<p>Example configuration:</p>
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<example>
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NameVirtualHost 111.22.33.44<br />
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<br />
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<VirtualHost 111.22.33.44><br />
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<indent>
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ServerName www.domain.tld<br />
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ServerPath /domain<br />
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DocumentRoot /web/domain<br />
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</indent>
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</VirtualHost><br />
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</example>
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<p>What does this mean? It means that a request for any URI
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beginning with "<code>/domain</code>" will be served from the
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virtual host <code>www.domain.tld</code>. This means that the
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pages can be accessed as <code>http://www.domain.tld/domain/</code>
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for all clients, although clients sending a <code>Host:</code> header
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can also access it as <code>http://www.domain.tld/</code>.</p>
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<p>In order to make this work, put a link on your primary
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virtual host's page to
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<code>http://www.domain.tld/domain/</code>. Then, in the virtual
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host's pages, be sure to use either purely relative links
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(<em>e.g.</em>, "<code>file.html</code>" or
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"<code>../icons/image.gif</code>") or links containing the
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prefacing <code>/domain/</code> (<em>e.g.</em>,
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"<code>http://www.domain.tld/domain/misc/file.html</code>" or
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"<code>/domain/misc/file.html</code>").</p>
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<p>This requires a bit of discipline, but adherence to these
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guidelines will, for the most part, ensure that your pages will
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work with all browsers, new and old.</p>
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</section>
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</manualpage>
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