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<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>. If you're planning to use

multiple ports (e.g. running SSL) you should add a Port to the argument,

such as <code>*:80</code>. 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

must match a defined <directive

module="core">NameVirtualHost</directive> directive. (In this usual case,

this will be "*:80"). 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>

<p>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.</p>

</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 *:80<br />

<br />

&lt;VirtualHost *:80&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 *:80&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>