manual/vhosts/name-based.html

	name-based.html revision 85939515009c2c78e391236bf825ded8609f6a1a
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML><HEAD>
<TITLE>Apache 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">Apache name-based Virtual Host Support</H1>

<STRONG>See Also:</STRONG>
<A HREF="ip-based.html">IP-based Virtual Host Support</A>

<HR>

<H2>Name-based vs. IP-based virtual hosts</H2>

<P>While the approach with IP-based virtual hosts works very well,
it is not the most elegant solution, because a dedicated IP address
is needed for every virtual host and it is hard to implement on some
machines. The <CODE>HTTP/1.1</CODE> protocol contains a method for the
server to identify what name it is being addressed as. Apache 1.1 and
later support this approach as well as the traditional
IP-address-per-hostname method.</P>

<P>The benefits of using the new name-based virtual host support is a
practically unlimited number of servers, ease of configuration and use, and
requires no additional hardware or software.
The main disadvantage is that the client must support this part of the
protocol. The latest versions of most browsers do, but there are still
old browsers in use who do not. This can cause problems, although a possible
solution is addressed below.</P>

<H2>Using non-IP Virtual Hosts</H2>

<P>Using the new virtual hosts is quite easy, and superficially looks
like the old method. You simply add to one of the Apache configuration
files (most likely <CODE>httpd.conf</CODE> or <CODE>srm.conf</CODE>)
code similar to the following:</P>
<PRE>
    NameVirtualHost 111.22.33.44

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

<P>The notable difference between IP-based and name-based virtual host
configuration is the
<A HREF="/mod/core.html#namevirtualhost"><CODE>NameVirtualHost</CODE></A>
directive which specifies an IP address that should be used as a target for
name-based virtual hosts.

<P>Of course, any additional directives can (and should) be placed
into the <CODE>&lt;VirtualHost&gt;</CODE> section. To make this work,
all that is needed is to make sure that the name
<SAMP>www.domain.tld</SAMP> points to the IP address
<SAMP>111.22.33.44</SAMP></P>

<p>Note: When you specify an IP address in a <code>NameVirtualHost</code>
directive then requests to that IP address will only ever be served
by matching &lt;VirtualHost&gt;s.  The "main server" will <b>never</b>
be served from the specified IP address.

<P>Additionally, many servers may wish to be accessible by more than
one name. For example, the example server might want to be accessible
as <CODE>domain.tld</CODE>, or <CODE>www2.domain.tld</CODE>, assuming
the IP addresses pointed to the same server. In fact, one might want it
so that all addresses at <CODE>domain.tld</CODE> were picked up by the
server. 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:</P>

<PRE>
    ServerAlias domain.tld *.domain.tld
</PRE>

<P>Note that you can use <CODE>*</CODE> and <CODE>?</CODE> as wild-card
characters.</P>

<P>You also might need <CODE>ServerAlias</CODE> if you are
serving local users who do not always include the domain name.
For example, if local users are
familiar with typing "www" or "www.foobar" then you will need to add
<CODE>ServerAlias www www.foobar</CODE>.  It isn't possible for the
server to know what domain the client uses for their name resolution
because the client doesn't provide that information in the request.</P>

<H2>Compatibility with Older Browsers</H2>

<P>As mentioned earlier, there are still some clients in use 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
<CITE>primary</CITE> name-based virtual host (the first virtual host
appearing in the configuration file for a specific IP address).</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:

<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 (e.g. "<SAMP>file.html</SAMP>" or
"<SAMP>/icons/image.gif</SAMP>" or links containing the prefacing
<SAMP>/domain/</SAMP>
(e.g. "<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>