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| <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. 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> |
| |
| <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#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. 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 <a |
| href="../mod/core.html#virtualhost"><VirtualHost></a> block for |
| each different host that you would like to serve. The argument to the |
| <code><VirtualHost></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><VirtualHost></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 an IP address |
| that the server is listening to. Then you simply add the following |
| to <code>httpd.conf</code>:</p> |
| |
| <pre> |
| NameVirtualHost * |
| |
| <VirtualHost *> |
| ServerName www.domain.tld |
| DocumentRoot /www/domain |
| </VirtualHost> |
| |
| <VirtualHost *> |
| ServerName www.otherdomain.tld |
| DocumentRoot /www/otherdomain |
| </VirtualHost> |
| </pre> |
| |
| <p>You can alternatively specify an explicit IP address in place of |
| the * in both the <code>NameVirtualHost</code> and |
| <code><VirtualHost></code> directives.</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 <VirtualHost> section. For |
| example if you add this to the first <VirtualHost> 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 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><VirtualHost></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><VirtualHost></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><VirtualHost></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><VirtualHost></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 |
| |
| <VirtualHost 111.22.33.44> |
| ServerName www.domain.tld |
| ServerPath /domain |
| DocumentRoot /web/domain |
| </VirtualHost> |
| </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> |
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