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23 <manualpage metafile="bind.xml.meta">
25 <title>Binding</title>
28 <p>Configuring Apache HTTP Server to listen on specific addresses and ports.</p>
31 <seealso><a href="vhosts/">Virtual Hosts</a></seealso>
32 <seealso><a href="dns-caveats.html">DNS Issues</a></seealso>
34 <section id="overview">
35 <title>Overview</title>
40 <module>mpm_common</module>
43 <directive module="core" type="section">VirtualHost</directive>
44 <directive module="mpm_common">Listen</directive>
49 <p>When httpd starts, it binds to some port and address on
50 the local machine and waits for incoming requests. By default,
51 it listens to all addresses on the machine. However, it may need to
52 be told to listen on specific ports, or only on selected
53 addresses, or a combination of both. This is often combined with the
54 <a href="vhosts.html">Virtual Host</a> feature, which determines how
55 <code>httpd</code> responds to different IP addresses, hostnames and
58 <p>The <directive module="mpm_common">Listen</directive>
59 directive tells the server to accept
60 incoming requests only on the specified port(s) or
61 address-and-port combinations. If only a port number is
62 specified in the <directive module="mpm_common">Listen</directive>
63 directive, the server listens to the given port on all interfaces.
64 If an IP address is given as well as a port, the server will listen
65 on the given port and interface. Multiple <directive
66 module="mpm_common">Listen</directive> directives may be used to
67 specify a number of addresses and ports to listen on. The
68 server will respond to requests from any of the listed
69 addresses and ports.</p>
71 <p>For example, to make the server accept connections on both
72 port 80 and port 8000, on all interfaces, use:</p>
79 <p>To make the server accept connections on port 80 for one interface,
80 and port 8000 on another, use</p>
83 Listen 192.0.2.1:80<br />
87 <p>IPv6 addresses must be enclosed in square brackets, as in the
88 following example:</p>
91 Listen [2001:db8::a00:20ff:fea7:ccea]:80
94 <note type="warning"><p>Overlapping <directive
95 module="mpm_common">Listen</directive> directives will result in a
96 fatal error which will prevent the server from starting up.</p>
99 (48)Address already in use: make_sock: could not bind to address [::]:80
106 <title>Special IPv6 Considerations</title>
108 <p>A growing number of platforms implement IPv6, and
109 <glossary>APR</glossary> supports IPv6 on most of these platforms,
110 allowing httpd to allocate IPv6 sockets, and to handle requests sent
113 <p>One complicating factor for httpd administrators is whether or
114 not an IPv6 socket can handle both IPv4 connections and IPv6
115 connections. Handling IPv4 connections with an IPv6 socket uses
116 IPv4-mapped IPv6 addresses, which are allowed by default on most
117 platforms, but are disallowed by default on FreeBSD, NetBSD, and
118 OpenBSD, in order to match the system-wide policy on those
119 platforms. On systems where it is disallowed by default, a
120 special <program>configure</program> parameter can change this behavior
123 <p>On the other hand, on some platforms, such as Linux and Tru64, the
124 <strong>only</strong> way to handle both IPv6 and IPv4 is to use
125 mapped addresses. If you want <code>httpd</code> to handle IPv4 and IPv6 connections
126 with a minimum of sockets, which requires using IPv4-mapped IPv6
127 addresses, specify the <code>--enable-v4-mapped</code> <program>
128 configure</program> option.</p>
130 <p><code>--enable-v4-mapped</code> is the default on all platforms except
131 FreeBSD, NetBSD, and OpenBSD, so this is probably how your httpd was
134 <p>If you want httpd to handle IPv4 connections only, regardless of
135 what your platform and APR will support, specify an IPv4 address on all
136 <directive module="mpm_common">Listen</directive> directives, as in the
137 following examples:</p>
140 Listen 0.0.0.0:80<br />
144 <p>If your platform supports it and you want httpd to handle IPv4 and
145 IPv6 connections on separate sockets (i.e., to disable IPv4-mapped
146 addresses), specify the <code>--disable-v4-mapped</code> <program>
147 configure</program> option. <code>--disable-v4-mapped</code> is the
148 default on FreeBSD, NetBSD, and OpenBSD.</p>
151 <section id="virtualhost">
152 <title>How This Works With Virtual Hosts</title>
155 module="mpm_common">Listen</directive> directive does not implement
156 Virtual Hosts - it only tells the
157 main server what addresses and ports to listen on. If no
158 <directive module="core" type="section">VirtualHost</directive>
159 directives are used, the server will behave
160 in the same way for all accepted requests. However,
161 <directive module="core" type="section">VirtualHost</directive>
162 can be used to specify a different behavior
163 for one or more of the addresses or ports. To implement a
164 VirtualHost, the server must first be told to listen to the
165 address and port to be used. Then a
166 <directive module="core" type="section">VirtualHost</directive> section
167 should be created for the specified address and port to set the
168 behavior of this virtual host. Note that if the
169 <directive module="core" type="section">VirtualHost</directive>
170 is set for an address and port that the
171 server is not listening to, it cannot be accessed.</p>