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<?xml version="1.0" encoding="ISO-8859-1"?>
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<title>Binding to Addresses and Ports - Apache HTTP Server Version 2.4</title>
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<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.4</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.4</a></div><div id="page-content"><div id="preamble"><h1>Binding to Addresses and Ports</h1>
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<p>Configuring Apache HTTP Server to listen on specific addresses and ports.</p>
</div>
<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#overview">Overview</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#reload">Changing Listen configuration on restart</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#ipv6">Special IPv6 Considerations</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#protocol">Specifying the protocol with Listen</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#virtualhost">How This Works With Virtual Hosts</a></li>
</ul><h3>See also</h3><ul class="seealso"><li><a href="vhosts/">Virtual Hosts</a></li><li><a href="dns-caveats.html">DNS Issues</a></li><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="overview" id="overview">Overview</a></h2>
<table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/core.html">core</a></code></li><li><code class="module"><a href="./mod/mpm_common.html">mpm_common</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/core.html#virtualhost"><VirtualHost></a></code></li><li><code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code></li></ul></td></tr></table>
<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 <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code>
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 <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code>
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 <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code> 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>
<div class="example"><pre class="prettyprint lang-config">Listen 80
Listen 8000</pre>
</div>
<p>To make the server accept connections on port 80 for one interface,
and port 8000 on another, use</p>
<div class="example"><pre class="prettyprint lang-config">Listen 192.0.2.1:80
Listen 192.0.2.5:8000</pre>
</div>
<p>IPv6 addresses must be enclosed in square brackets, as in the
following example:</p>
<div class="example"><pre class="prettyprint lang-config">Listen [2001:db8::a00:20ff:fea7:ccea]:80</pre>
</div>
<div class="warning"><p>Overlapping <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code> directives will result in a
fatal error which will prevent the server from starting up.</p>
<div class="example"><p><code>
(48)Address already in use: make_sock: could not bind to address [::]:80
</code></p></div>
<p>See <a href="http://wiki.apache.org/httpd/CouldNotBindToAddress">the
discussion in the wiki</a> for further troubleshooting tips.</p>
</div>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="reload" id="reload">Changing Listen configuration on restart</a></h2>
<p>When httpd is restarted, special consideration must be made for
changes to <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code> directives. During a restart, httpd keeps ports
bound (as in the original configuration) to avoid generating
"Connection refused" errors for any new attempts to connect to the
server. If changes are made to the set of <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code> directives used
which conflict with the old configuration, configuration will fail
and the server will terminate.</p>
<p>For example, changing from configuration:</p>
<div class="example"><pre class="prettyprint lang-config">Listen 127.0.0.1:80</pre>
</div>
<p>to the following may fail, because binding to port 80 across
all addresses conflicts with binding to port 80 on just
127.0.0.1.</p>
<div class="example"><pre class="prettyprint lang-config">Listen 80</pre>
</div>
<p>To have such configuration changes take effect, it is necessary
to stop and then start the server.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="ipv6" id="ipv6">Special IPv6 Considerations</a></h2>
<p>A growing number of platforms implement IPv6, and
<a class="glossarylink" href="./glossary.html#apr" title="see glossary">APR</a> 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 <code class="program"><a href="./programs/configure.html">configure</a></code> 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> <code class="program"><a href="./programs/configure.html">configure</a></code> 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
<code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code> directives, as in the
following examples:</p>
<div class="example"><pre class="prettyprint lang-config">Listen 0.0.0.0:80
Listen 192.0.2.1:80</pre>
</div>
<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> <code class="program"><a href="./programs/configure.html">configure</a></code> option. <code>--disable-v4-mapped</code> is the
default on FreeBSD, NetBSD, and OpenBSD.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="protocol" id="protocol">Specifying the protocol with Listen</a></h2>
<p>The optional second <var>protocol</var> argument of
<code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code>
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
<code class="directive"><a href="./mod/core.html#acceptfilter">AcceptFilter</a></code> 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>
<div class="example"><pre class="prettyprint lang-config">Listen 192.170.2.1:8443 https</pre>
</div>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="virtualhost" id="virtualhost">How This Works With Virtual Hosts</a></h2>
<p> The <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code> directive does not implement
Virtual Hosts - it only tells the
main server what addresses and ports to listen on. If no
<code class="directive"><a href="./mod/core.html#virtualhost"><VirtualHost></a></code>
directives are used, the server will behave
in the same way for all accepted requests. However,
<code class="directive"><a href="./mod/core.html#virtualhost"><VirtualHost></a></code>
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
<code class="directive"><a href="./mod/core.html#virtualhost"><VirtualHost></a></code> section
should be created for the specified address and port to set the
behavior of this virtual host. Note that if the
<code class="directive"><a href="./mod/core.html#virtualhost"><VirtualHost></a></code>
is set for an address and port that the
server is not listening to, it cannot be accessed.</p>
</div></div>
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</div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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