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--><title>Binding - Apache HTTP Server</title><link href="/style/manual.css" type="text/css" rel="stylesheet"/></head><body><blockquote><div align="center"><img src="/images/sub.gif" alt="[APACHE DOCUMENTATION]"/><h3>Apache HTTP Server Version 2.0</h3></div><h1 align="center">Binding</h1>
<p>Configuring Apache to listen on specific addresses and ports.</p>
<ul><li><a href="#overview">Overview</a></li><li><a href="#ipv6">Special IPv6 Considerations</a></li><li><a href="#virtualhost">How This Works With Virtual Hosts</a></li></ul><hr/><p><strong>See also </strong></p><ul><li><a href="vhosts/">Virtual Hosts</a></li><li><a href="dns-caveats.html">DNS Issues</a></li></ul><h2><a name="overview">Overview</a></h2>
<table border="1"><tr><td valign="top"><strong>Related Modules</strong><br/><br/><code><a href="/mod/core.html">core</a></code><br/><code><a href="/mod/mpm_common.html">mpm_common</a></code><br/></td><td valign="top"><strong>Related Directives</strong><br/><br/><a href="/mod/core.html#virtualhost" class="directive"><code class="directive">VirtualHost</code></a><br/><a href="/mod/mpm_common.html#listen" class="directive"><code class="directive">Listen</code></a><br/></td></tr></table>
<p>When Apache 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 needs to
be told to listen on specific ports, or to listen on only selected
addresses, or a combination. This is often combined with the
Virtual Host feature which determines how Apache responds to
different IP addresses, hostnames and ports.</p>
<p>The <a href="/mod/mpm_common.html#listen" class="directive"><code class="directive">Listen</code></a>
directive tells the server to accept
incoming requests only on the specified port or
address-and-port combinations. If only a port number is
specified in the <a href="/mod/mpm_common.html#listen" class="directive"><code class="directive">Listen</code></a>
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 Listen 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, use:</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen 80<br>
Listen 8000
</code></td></tr></table></blockquote>
<p>To make the server accept connections on two specified
interfaces and port numbers, use</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen 192.170.2.1:80<br>
Listen 192.170.2.5:8000
</code></td></tr></table></blockquote>
<p>IPv6 addresses must be surrounded in square brackets, as in the
following example:</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen [fe80::a00:20ff:fea7:ccea]:80
</code></td></tr></table></blockquote>
<h2><a name="ipv6">Special IPv6 Considerations</a></h2>
<p>When APR supports IPv6, Apache will create IPv6-capable listening
sockets by default (i.e., when no IP address is specified on the
Listen directive). In other words, when APR supports IPv6,</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen 80
</code></td></tr></table></blockquote>
<p>is equivalent to</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen [::]:80
</code></td></tr></table></blockquote>
<p>When APR does not support IPv6,</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen 80
</code></td></tr></table></blockquote>
<p>is equivalent to</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen 0.0.0.0:80
</code></td></tr></table></blockquote>
<p>On some platforms, such as NetBSD, binding to the IPv6 wildcard address
("::") does not allow Apache to accept connections on IPv4 interfaces.
In this situation, multiple Listen directives are required, as shown
below:</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Listen 0.0.0.0:80<br>
Listen [::]:0
</code></td></tr></table></blockquote>
<p>Apache does not currently detect this, so the Listen statements must
be edited manually by the administrator.</p>
<h2><a name="virtualhost">How This Works With Virtual Hosts</a></h2>
<p>Listen does not implement Virtual Hosts. It only tells the
main server what addresses and ports to listen to. If no
<a href="/mod/core.html#virtualhost" class="directive"><code class="directive"><VirtualHost></code></a>
directives are used, the server will behave
the same for all accepted requests. However,
<a href="/mod/core.html#virtualhost" class="directive"><code class="directive"><VirtualHost></code></a>
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
<a href="/mod/core.html#virtualhost" class="directive"><code class="directive"><VirtualHost></code></a> section
should be created for a specified address and port to set the
behavior of this virtual host. Note that if the
<a href="/mod/core.html#virtualhost" class="directive"><code class="directive"><VirtualHost></code></a>
is set for an address and port that the
server is not listening to, it cannot be accessed.</p>
