1 <?xml version="1.0" encoding="UTF-8" ?>
2 <!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
3 <?xml-stylesheet type="text/xsl" href="./style/manual.en.xsl"?>
4 <!-- $LastChangedRevision$ -->
7 Licensed to the Apache Software Foundation (ASF) under one or more
8 contributor license agreements. See the NOTICE file distributed with
9 this work for additional information regarding copyright ownership.
10 The ASF licenses this file to You under the Apache License, Version 2.0
11 (the "License"); you may not use this file except in compliance with
12 the License. You may obtain a copy of the License at
14 http://www.apache.org/licenses/LICENSE-2.0
16 Unless required by applicable law or agreed to in writing, software
17 distributed under the License is distributed on an "AS IS" BASIS,
18 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
19 See the License for the specific language governing permissions and
20 limitations under the License.
23 <manualpage metafile="bind.xml.meta">
25 <title>Binding to Addresses and Ports</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/">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>
75 <highlight language="config">
81 <p>To make the server accept connections on port 80 for one interface,
82 and port 8000 on another, use</p>
85 <highlight language="config">
91 <p>IPv6 addresses must be enclosed in square brackets, as in the
92 following example:</p>
95 <highlight language="config">
96 Listen [2001:db8::a00:20ff:fea7:ccea]:80
100 <note type="warning"><p>Overlapping <directive
101 module="mpm_common">Listen</directive> directives will result in a
102 fatal error which will prevent the server from starting up.</p>
105 (48)Address already in use: make_sock: could not bind to address [::]:80
109 href="http://wiki.apache.org/httpd/CouldNotBindToAddress">the
110 discussion in the wiki</a> for further troubleshooting tips.</p>
116 <section id="reload">
117 <title>Changing Listen configuration on restart</title>
119 <p>When httpd is restarted, special consideration must be made for
120 changes to <directive module="mpm_common">Listen</directive> directives. During a restart, httpd keeps ports
121 bound (as in the original configuration) to avoid generating
122 "Connection refused" errors for any new attempts to connect to the
123 server. If changes are made to the set of <directive module="mpm_common">Listen</directive> directives used
124 which conflict with the old configuration, configuration will fail
125 and the server will terminate.</p>
127 <p>For example, changing from configuration:</p>
130 <highlight language="config">
135 <p>to the following may fail, because binding to port 80 across
136 all addresses conflicts with binding to port 80 on just
140 <highlight language="config">
145 <p>To have such configuration changes take effect, it is necessary
146 to stop and then start the server.</p>
151 <title>Special IPv6 Considerations</title>
153 <p>A growing number of platforms implement IPv6, and
154 <glossary>APR</glossary> supports IPv6 on most of these platforms,
155 allowing httpd to allocate IPv6 sockets, and to handle requests sent
158 <p>One complicating factor for httpd administrators is whether or
159 not an IPv6 socket can handle both IPv4 connections and IPv6
160 connections. Handling IPv4 connections with an IPv6 socket uses
161 IPv4-mapped IPv6 addresses, which are allowed by default on most
162 platforms, but are disallowed by default on FreeBSD, NetBSD, and
163 OpenBSD, in order to match the system-wide policy on those
164 platforms. On systems where it is disallowed by default, a
165 special <program>configure</program> parameter can change this behavior
168 <p>On the other hand, on some platforms, such as Linux and Tru64, the
169 <strong>only</strong> way to handle both IPv6 and IPv4 is to use
170 mapped addresses. If you want <code>httpd</code> to handle IPv4 and IPv6 connections
171 with a minimum of sockets, which requires using IPv4-mapped IPv6
172 addresses, specify the <code>--enable-v4-mapped</code> <program>
173 configure</program> option.</p>
175 <p><code>--enable-v4-mapped</code> is the default on all platforms except
176 FreeBSD, NetBSD, and OpenBSD, so this is probably how your httpd was
179 <p>If you want httpd to handle IPv4 connections only, regardless of
180 what your platform and APR will support, specify an IPv4 address on all
181 <directive module="mpm_common">Listen</directive> directives, as in the
182 following examples:</p>
185 <highlight language="config">
191 <p>If your platform supports it and you want httpd to handle IPv4 and
192 IPv6 connections on separate sockets (i.e., to disable IPv4-mapped
193 addresses), specify the <code>--disable-v4-mapped</code> <program>
194 configure</program> option. <code>--disable-v4-mapped</code> is the
195 default on FreeBSD, NetBSD, and OpenBSD.</p>
198 <section id="protocol">
199 <title>Specifying the protocol with Listen</title>
200 <p>The optional second <var>protocol</var> argument of
201 <directive module="mpm_common">Listen</directive>
202 is not required for most
203 configurations. If not specified, <code>https</code> is the default for
204 port 443 and <code>http</code> the default for all other ports. The
205 protocol is used to determine which module should handle a request, and
206 to apply protocol specific optimizations with the
207 <directive module="core">AcceptFilter</directive> directive.</p>
209 <p>You only need to set the protocol if you are running on non-standard
210 ports. For example, running an <code>https</code> site on port 8443:</p>
213 <highlight language="config">
214 Listen 192.170.2.1:8443 https
219 <section id="virtualhost">
220 <title>How This Works With Virtual Hosts</title>
223 module="mpm_common">Listen</directive> directive does not implement
224 Virtual Hosts - it only tells the
225 main server what addresses and ports to listen on. If no
226 <directive module="core" type="section">VirtualHost</directive>
227 directives are used, the server will behave
228 in the same way for all accepted requests. However,
229 <directive module="core" type="section">VirtualHost</directive>
230 can be used to specify a different behavior
231 for one or more of the addresses or ports. To implement a
232 VirtualHost, the server must first be told to listen to the
233 address and port to be used. Then a
234 <directive module="core" type="section">VirtualHost</directive> section
235 should be created for the specified address and port to set the
236 behavior of this virtual host. Note that if the
237 <directive module="core" type="section">VirtualHost</directive>
238 is set for an address and port that the
239 server is not listening to, it cannot be accessed.</p>