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.
IPv6 addresses must be
specified in square brackets because the optional port number could not be
determined otherwise. An IPv6 example is shown below:
Search the Knowledgebase
Browse by Category
Print this page
Email this page
Post a comment
Subscribe me
Add to favorites
Remove Highlighting
Edit this Article