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How to configure Apache to use IPv6


When the httpd service starts, it binds to some ports and addresses on the local machine and waits for the incoming requests. In the httpd.conf file you can specify specific ports to listen only on specific addresses. This is used by the Listen directive, it tells the server to accept incoming requests only on the specified port and/or address and port combinations. You can use multiple Listen directives to specify a number of ports and or addresses to listen on. The server will respond to requests from any listed addresses and or ports.

The following is an example for a Listen directive to accept connections on port 80 for an IPv4 address:

  • Listen 192.168.1.100:80

The following is an example for a Listen directive to accept connections on port 80 for an IPv6 Address.
Notice that the IPv6 address needs to be surrounded in square brackets, as below.

  • Listen [2001:db8::a00:20ff:fea7:ccea]:80

Special IPv6 Considerations

A growing number of platforms implement IPv6, and APR supports IPv6 on most of these platforms, allowing Apache to allocate IPv6 sockets and handle requests which were sent over IPv6. One complicating factor for Apache administrators is whether or not an IPv6 socket can handle both IPv4 connections and IPv6 connections. Handling IPv4 connections with an IPv6 socket uses IPv4-mapped IPv6 addresses, which are allowed by default on most platforms but are disallowed by default on FreeBSD, NetBSD, and OpenBSD in order to match the system-wide policy on those platforms. But even on systems where it is disallowed by default, a special configure parameter can change this behavior for Apache.

If you want Apache to handle IPv4 and IPv6 connections with a minimum of sockets, which require using IPv4-mapped IPv6 addresses, specify the --enable-v4-mapped configure option and use generic Listen directives like the following:

  • Listen 80

With -enable-v4-mapped, the Listen directives in the default configuration file created by Apache will use this form. --enable-v4-mapped is the default on all platforms but FreeBSD, NetBSD, and OpenBSD, so this is probably how your Apache was built.

If you want Apache to handle IPv4 connections only, regardless of what your platform and APR will support, specify an IPv4 address on all Listen directives, as in the following examples:

  • Listen 0.0.0.0:80
  • Listen 192.168.1.100:80

If you want Apache to handle IPv4 and IPv6 connections on separate sockets (i.e., to disable IPv4-mapped addresses), specify the --disable-v4-mapped configure option and use specific Listen directives like the following:

  • Listen :::80
  • Listen 0.0.0.0:80

With -disable-v4-mapped, the Listen directives in the default configuration file created by Apache will use this form. --disable-v4-mapped is the default on FreeBSD, NetBSD, and OpenBSD.

How this works with Virtual Hosts?

Listen does not implement Virtual Hosts. It only tells the main server what addresses and ports to listen to. If no <VirtualHost> directives are used, the server will behave the same for all accepted requests. However, <VirtualHost> can be used to specify a different behavior for one or more of the addresses and ports. To implement a VirtualHost, the server must first be told to listen to the address and port to be used. Then a <VirtualHost> section should be created for a specified address and port to set the behavior of this virtual host. Note that if the <VirtualHost> is set for an address and port that the server is not listening to, it cannot be accessed.

Examples

<VirtualHost 10.1.2.3>
ServerAdmin webmaster@host.foo.com
DocumentRoot /www/docs/host.foo.com
ServerName host.foo.com
ErrorLog logs/host.foo.com-error_log
TransferLog logs/host.foo.com-access_log
</VirtualHost>

IPv6 addresses must be specified in square brackets because the optional port number could not be determined otherwise. An IPv6 example is shown below:

<VirtualHost §e07a29e44f749f4f75046d0afd006480§
ServerAdmin webmaster@host.example.com
DocumentRoot /www/docs/host.example.com
ServerName host.example.com
ErrorLog logs/host.example.com-error_log
TransferLog logs/host.example.com-access_log
</VirtualHost>


Source: The Apache Software Foundation 2.0 documentation.