Name-based Virtual Host Support
This document describes when and how to use name-based virtual hosts.
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.
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:
- 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
- Name-based virtual hosting cannot be used with SSL secure servers
because of the nature of the SSL protocol.
- Some operating systems and network equipment implement bandwidth
management techniques that cannot differentiate between hosts unless
they are on separate IP addresses.
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
In the normal case where any and all IP addresses on the server should
be used, you can use
* as the argument to
NameVirtualHost. If you're planning to use
multiple ports (e.g. running SSL) you should add a Port to the argument,
*:80. Note that mentioning an IP address in a
NameVirtualHost directive does not
automatically make the server listen to that IP address. See
Setting which addresses and ports Apache uses
for more details. In addition, any IP address specified here must be
associated with a network interface on the server.
The next step is to create a
<VirtualHost> block for
each different host that you would like to serve. The argument to the
should be the same as the argument to the
NameVirtualHost directive (ie, an IP address,
* for all addresses). Inside each
<VirtualHost> block, you will need at minimum a
ServerName directive to designate
which host is served and a
directive to show where in the filesystem the content for that host
Main host goes away
If you are adding virtual hosts to an existing web server, you
must also create a
<VirtualHost> block for the existing host. The
DocumentRoot included in this virtual host should be the
same as the global
DocumentRoot. List this virtual
host first in the configuration file so that it will act as the default
For example, suppose that you are serving the domain
www.domain.tld and you wish to add the virtual host
www.otherdomain.tld, which points at the same IP address.
Then you simply add the following to
ServerAlias domain.tld *.domain.tld
You can alternatively specify an explicit IP address in place of the
* in both the
<VirtualHost> 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.
Many servers want to be accessible by more than one name. This is
possible with the
directive, placed inside the
<VirtualHost> section. For example in the first
<VirtualHost> block above, the
ServerAlias directive indicates that
the listed names are other names which people can use to see that same
ServerAlias domain.tld *.domain.tld
then requests for all hosts in the
domain.tld domain will
be served by the
www.domain.tld virtual host. The wildcard
? can be used to match names.
Of course, you can't just make up names and place them in
ServerAlias. You must
first have your DNS server properly configured to map those names to an IP
address associated with your server.
Finally, you can fine-tune the configuration of the virtual hosts
by placing other directives inside the
<VirtualHost> 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 Context of the
directive. Configuration directives set in the main server context
container) will be used only if they are not overridden by the virtual host
Now when a request arrives, the server will first check if it is using
an IP address that matches the
NameVirtualHost. If it is, then it will look at each
<VirtualHost> section with a matching
IP address and try to find one where the
ServerAlias matches the requested
hostname. If it finds one, then it uses the configuration for that server.
If no matching virtual host is found, then the first listed virtual
host that matches the IP address will be used.
As a consequence, the first listed virtual host is the default
virtual host. The
the main server will never be used when an IP
address matches the
directive. If you would like to have a special configuration for requests
that do not match any particular virtual host, simply put that configuration
container and list it first in the configuration file.
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 primary name-based virtual host).
How much older?
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
Host header as
required for name-based virtual hosts.
There is a possible workaround with the
directive, albeit a slightly cumbersome one:
What does this mean? It means that a request for any URI
beginning with "
/domain" will be served from the
www.domain.tld. This means that the
pages can be accessed as
for all clients, although clients sending a
can also access it as
In order to make this work, put a link on your primary
virtual host's page to
http://www.domain.tld/domain/. Then, in the virtual
host's pages, be sure to use either purely relative links
../icons/image.gif") or links containing the
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.