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<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
<?xml-stylesheet type="text/xsl" href="./style/manual.en.xsl"?>
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<manualpage metafile="bind.xml.meta">
<title>Binding to Addresses and Ports</title>
<summary>
<p>Configuring Apache HTTP Server to listen on specific addresses and ports.</p>
</summary>
<seealso><a href="vhosts/">Virtual Hosts</a></seealso>
<seealso><a href="dns-caveats.html">DNS Issues</a></seealso>
<section id="overview">
<title>Overview</title>
<related>
<modulelist>
<module>core</module>
<module>mpm_common</module>
</modulelist>
<directivelist>
<directive module="core" type="section">VirtualHost</directive>
<directive module="mpm_common">Listen</directive>
</directivelist>
</related>
<p>When httpd starts, it binds to some port and address on
the local machine and waits for incoming requests. By default,
it listens to all addresses on the machine. However, it may need to
be told to listen on specific ports, or only on selected
addresses, or a combination of both. This is often combined with the
<a href="vhosts">Virtual Host</a> feature, which determines how
<code>httpd</code> responds to different IP addresses, hostnames and
ports.</p>
<p>The <directive module="mpm_common">Listen</directive>
directive tells the server to accept
incoming requests only on the specified port(s) or
address-and-port combinations. If only a port number is
specified in the <directive module="mpm_common">Listen</directive>
directive, the server listens to the given port on all interfaces.
If an IP address is given as well as a port, the server will listen
on the given port and interface. Multiple <directive
module="mpm_common">Listen</directive> directives may be used to
specify a number of addresses and ports to listen on. The
server will respond to requests from any of the listed
addresses and ports.</p>
<p>For example, to make the server accept connections on both
port 80 and port 8000, on all interfaces, use:</p>
<highlight language="config">
Listen 80
Listen 8000
</highlight>
<p>To make the server accept connections on port 80 for one interface,
and port 8000 on another, use</p>
<highlight language="config">
Listen 192.0.2.1:80
Listen 192.0.2.5:8000
</highlight>
<p>IPv6 addresses must be enclosed in square brackets, as in the
following example:</p>
<highlight language="config">
Listen [2001:db8::a00:20ff:fea7:ccea]:80
</highlight>
<note type="warning"><p>Overlapping <directive
module="mpm_common">Listen</directive> directives will result in a
fatal error which will prevent the server from starting up.</p>
<example>
(48)Address already in use: make_sock: could not bind to address [::]:80
</example>
</note>
</section>
<section id="ipv6">
<title>Special IPv6 Considerations</title>
<p>A growing number of platforms implement IPv6, and
<glossary>APR</glossary> supports IPv6 on most of these platforms,
allowing httpd to allocate IPv6 sockets, and to handle requests sent
over IPv6.</p>
<p>One complicating factor for httpd 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. On systems where it is disallowed by default, a
special <program>configure</program> parameter can change this behavior
for httpd.</p>
<p>On the other hand, on some platforms, such as Linux and Tru64, the
<strong>only</strong> way to handle both IPv6 and IPv4 is to use
mapped addresses. If you want <code>httpd</code> to handle IPv4 and IPv6 connections
with a minimum of sockets, which requires using IPv4-mapped IPv6
addresses, specify the <code>--enable-v4-mapped</code> <program>
configure</program> option.</p>
<p><code>--enable-v4-mapped</code> is the default on all platforms except
FreeBSD, NetBSD, and OpenBSD, so this is probably how your httpd was
built.</p>
<p>If you want httpd to handle IPv4 connections only, regardless of
what your platform and APR will support, specify an IPv4 address on all
<directive module="mpm_common">Listen</directive> directives, as in the
following examples:</p>
<highlight language="config">
Listen 0.0.0.0:80
Listen 192.0.2.1:80
</highlight>
<p>If your platform supports it and you want httpd to handle IPv4 and
IPv6 connections on separate sockets (i.e., to disable IPv4-mapped
addresses), specify the <code>--disable-v4-mapped</code> <program>
configure</program> option. <code>--disable-v4-mapped</code> is the
default on FreeBSD, NetBSD, and OpenBSD.</p>
</section>
<section id="protocol">
<title>Specifying the protocol with Listen</title>
<p>The optional second <var>protocol</var> argument of
<directive module="mpm_common">Listen</directive>
is not required for most
configurations. If not specified, <code>https</code> is the default for
port 443 and <code>http</code> the default for all other ports. The
protocol is used to determine which module should handle a request, and
to apply protocol specific optimizations with the
<directive module="core">AcceptFilter</directive> directive.</p>
<p>You only need to set the protocol if you are running on non-standard
ports. For example, running an <code>https</code> site on port 8443:</p>
<highlight language="config">
Listen 192.170.2.1:8443 https
</highlight>
</section>
<section id="virtualhost">
<title>How This Works With Virtual Hosts</title>
<p> The <directive
module="mpm_common">Listen</directive> directive does not implement
Virtual Hosts - it only tells the
main server what addresses and ports to listen on. If no
<directive module="core" type="section">VirtualHost</directive>
directives are used, the server will behave
in the same way for all accepted requests. However,
<directive module="core" type="section">VirtualHost</directive>
can be used to specify a different behavior
for one or more of the addresses or ports. To implement a
VirtualHost, the server must first be told to listen to the
address and port to be used. Then a
<directive module="core" type="section">VirtualHost</directive> section
should be created for the specified address and port to set the
behavior of this virtual host. Note that if the
<directive module="core" type="section">VirtualHost</directive>
is set for an address and port that the
server is not listening to, it cannot be accessed.</p>
</section>
</manualpage>
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