Gecko [ www.jdcpatala.org ]

Name	Size	Permission
developer	[ DIR ]	drwxr-xr-x
faq	[ DIR ]	drwxr-xr-x
howto	[ DIR ]	drwxr-xr-x
images	[ DIR ]	drwxr-xr-x
misc	[ DIR ]	drwxr-xr-x
mod	[ DIR ]	drwxr-xr-x
platform	[ DIR ]	drwxr-xr-x
programs	[ DIR ]	drwxr-xr-x
rewrite	[ DIR ]	drwxr-xr-x
ssl	[ DIR ]	drwxr-xr-x
style	[ DIR ]	drwxr-xr-x
vhosts	[ DIR ]	drwxr-xr-x
BUILDING	102 B	-rw-r--r--
LICENSE	11.09 KB	-rw-r--r--
bind.html	538 B	-rw-r--r--
bind.html.de	15.28 KB	-rw-r--r--
bind.html.en	15.19 KB	-rw-r--r--
bind.html.fr.utf8	16.49 KB	-rw-r--r--
bind.html.ja.utf8	14.34 KB	-rw-r--r--
bind.html.ko.euc-kr	10.95 KB	-rw-r--r--
bind.html.tr.utf8	16.21 KB	-rw-r--r--
caching.html	292 B	-rw-r--r--
caching.html.en	50.66 KB	-rw-r--r--
caching.html.fr.utf8	56.43 KB	-rw-r--r--
caching.html.tr.utf8	54.69 KB	-rw-r--r--
configuring.html	580 B	-rw-r--r--
configuring.html.de	16.71 KB	-rw-r--r--
configuring.html.en	17.36 KB	-rw-r--r--
configuring.html.fr.utf8	18.84 KB	-rw-r--r--
configuring.html.ja.utf8	16.98 KB	-rw-r--r--
configuring.html.ko.euc-kr	13.71 KB	-rw-r--r--
configuring.html.tr.utf8	18.57 KB	-rw-r--r--
content-negotiation.html	529 B	-rw-r--r--
content-negotiation.html.en	33.75 KB	-rw-r--r--
content-negotiation.html.fr.ut...	38.73 KB	-rw-r--r--
content-negotiation.html.ja.ut...	40.97 KB	-rw-r--r--
content-negotiation.html.ko.eu...	28.48 KB	-rw-r--r--
content-negotiation.html.tr.ut...	37.08 KB	-rw-r--r--
convenience.map	36.73 KB	-rw-r--r--
custom-error.html	586 B	-rw-r--r--
custom-error.html.en	13.58 KB	-rw-r--r--
custom-error.html.es	13.3 KB	-rw-r--r--
custom-error.html.fr.utf8	14.51 KB	-rw-r--r--
custom-error.html.ja.utf8	13.21 KB	-rw-r--r--
custom-error.html.ko.euc-kr	11.52 KB	-rw-r--r--
custom-error.html.tr.utf8	14.17 KB	-rw-r--r--
dns-caveats.html	489 B	-rw-r--r--
dns-caveats.html.en	12.37 KB	-rw-r--r--
dns-caveats.html.fr.utf8	13.39 KB	-rw-r--r--
dns-caveats.html.ja.utf8	17.37 KB	-rw-r--r--
dns-caveats.html.ko.euc-kr	13.47 KB	-rw-r--r--
dns-caveats.html.tr.utf8	12.79 KB	-rw-r--r--
dso.html	449 B	-rw-r--r--
dso.html.en	19.27 KB	-rw-r--r--
dso.html.fr.utf8	22.21 KB	-rw-r--r--
dso.html.ja.utf8	23.28 KB	-rw-r--r--
dso.html.ko.euc-kr	16.59 KB	-rw-r--r--
dso.html.tr.utf8	21.48 KB	-rw-r--r--
env.html	449 B	-rw-r--r--
env.html.en	30.62 KB	-rw-r--r--
env.html.fr.utf8	33.06 KB	-rw-r--r--
env.html.ja.utf8	30.56 KB	-rw-r--r--
env.html.ko.euc-kr	22.14 KB	-rw-r--r--
env.html.tr.utf8	32.71 KB	-rw-r--r--
expr.html	199 B	-rw-r--r--
expr.html.en	36.03 KB	-rw-r--r--
expr.html.fr.utf8	38.48 KB	-rw-r--r--
filter.html	550 B	-rw-r--r--
filter.html.en	14.84 KB	-rw-r--r--
filter.html.es	17.28 KB	-rw-r--r--
filter.html.fr.utf8	16.01 KB	-rw-r--r--
filter.html.ja.utf8	9.23 KB	-rw-r--r--
filter.html.ko.euc-kr	8.37 KB	-rw-r--r--
filter.html.tr.utf8	16 KB	-rw-r--r--
getting-started.html	316 B	-rw-r--r--
getting-started.html.en	15.22 KB	-rw-r--r--
getting-started.html.fr.utf8	17.18 KB	-rw-r--r--
getting-started.html.ru.utf8	21.27 KB	-rw-r--r--
glossary.html	650 B	-rw-r--r--
glossary.html.de	34.8 KB	-rw-r--r--
glossary.html.en	30.02 KB	-rw-r--r--
glossary.html.es	31.97 KB	-rw-r--r--
glossary.html.fr.utf8	34.01 KB	-rw-r--r--
glossary.html.ja.utf8	32.03 KB	-rw-r--r--
glossary.html.ko.euc-kr	20.88 KB	-rw-r--r--
glossary.html.tr.utf8	33.11 KB	-rw-r--r--
handler.html	649 B	-rw-r--r--
handler.html.en	11.79 KB	-rw-r--r--
handler.html.es	12.72 KB	-rw-r--r--
handler.html.fr.utf8	12.6 KB	-rw-r--r--
handler.html.ja.utf8	13.36 KB	-rw-r--r--
handler.html.ko.euc-kr	11.35 KB	-rw-r--r--
handler.html.tr.utf8	12.39 KB	-rw-r--r--
handler.html.zh-cn.utf8	11.34 KB	-rw-r--r--
index.html	981 B	-rw-r--r--
index.html.da	8.85 KB	-rw-r--r--
index.html.de	9.28 KB	-rw-r--r--
index.html.en	9.11 KB	-rw-r--r--
index.html.es	9.75 KB	-rw-r--r--
index.html.fr.utf8	9.47 KB	-rw-r--r--
index.html.ja.utf8	9.55 KB	-rw-r--r--
index.html.ko.euc-kr	8.23 KB	-rw-r--r--
index.html.pt-br	9.26 KB	-rw-r--r--
index.html.ru.utf8	10.41 KB	-rw-r--r--
index.html.tr.utf8	9.34 KB	-rw-r--r--
index.html.zh-cn.utf8	8.85 KB	-rw-r--r--
install.html	643 B	-rw-r--r--
install.html.de	25.56 KB	-rw-r--r--
install.html.en	26.97 KB	-rw-r--r--
install.html.es	29.38 KB	-rw-r--r--
install.html.fr.utf8	29.42 KB	-rw-r--r--
install.html.ja.utf8	27.58 KB	-rw-r--r--
install.html.ko.euc-kr	19.83 KB	-rw-r--r--
install.html.tr.utf8	29.06 KB	-rw-r--r--
invoking.html	650 B	-rw-r--r--
invoking.html.de	13.91 KB	-rw-r--r--
invoking.html.en	12.55 KB	-rw-r--r--
invoking.html.es	13.9 KB	-rw-r--r--
invoking.html.fr.utf8	13.42 KB	-rw-r--r--
invoking.html.ja.utf8	14.04 KB	-rw-r--r--
invoking.html.ko.euc-kr	10.87 KB	-rw-r--r--
invoking.html.tr.utf8	13.39 KB	-rw-r--r--
license.html	118 B	-rw-r--r--
license.html.en	15.49 KB	-rw-r--r--
logs.html	454 B	-rw-r--r--
logs.html.en	39.03 KB	-rw-r--r--
logs.html.fr.utf8	44.23 KB	-rw-r--r--
logs.html.ja.utf8	40.13 KB	-rw-r--r--
logs.html.ko.euc-kr	29.03 KB	-rw-r--r--
logs.html.tr.utf8	42.61 KB	-rw-r--r--
mpm.html	704 B	-rw-r--r--
mpm.html.de	11.13 KB	-rw-r--r--
mpm.html.en	13.26 KB	-rw-r--r--
mpm.html.es	10.46 KB	-rw-r--r--
mpm.html.fr.utf8	14.37 KB	-rw-r--r--
mpm.html.ja.utf8	11.7 KB	-rw-r--r--
mpm.html.ko.euc-kr	9.77 KB	-rw-r--r--
mpm.html.tr.utf8	14.19 KB	-rw-r--r--
mpm.html.zh-cn.utf8	11.26 KB	-rw-r--r--
new_features_2_0.html	712 B	-rw-r--r--
new_features_2_0.html.de	17.67 KB	-rw-r--r--
new_features_2_0.html.en	15.55 KB	-rw-r--r--
new_features_2_0.html.fr.utf8	18.27 KB	-rw-r--r--
new_features_2_0.html.ja.utf8	18.56 KB	-rw-r--r--
new_features_2_0.html.ko.euc-k...	14.52 KB	-rw-r--r--
new_features_2_0.html.pt-br	17.4 KB	-rw-r--r--
new_features_2_0.html.tr.utf8	17.37 KB	-rw-r--r--
new_features_2_2.html	520 B	-rw-r--r--
new_features_2_2.html.en	18.58 KB	-rw-r--r--
new_features_2_2.html.fr.utf8	20.73 KB	-rw-r--r--
new_features_2_2.html.ko.euc-k...	9.46 KB	-rw-r--r--
new_features_2_2.html.pt-br	10.81 KB	-rw-r--r--
new_features_2_2.html.tr.utf8	20.42 KB	-rw-r--r--
new_features_2_4.html	319 B	-rw-r--r--
new_features_2_4.html.en	28.17 KB	-rw-r--r--
new_features_2_4.html.fr.utf8	31.61 KB	-rw-r--r--
new_features_2_4.html.tr.utf8	30.66 KB	-rw-r--r--
sections.html	474 B	-rw-r--r--
sections.html.en	37.51 KB	-rw-r--r--
sections.html.fr.utf8	41.64 KB	-rw-r--r--
sections.html.ja.utf8	32.81 KB	-rw-r--r--
sections.html.ko.euc-kr	25.12 KB	-rw-r--r--
sections.html.tr.utf8	41.4 KB	-rw-r--r--
server-wide.html	489 B	-rw-r--r--
server-wide.html.en	11.88 KB	-rw-r--r--
server-wide.html.fr.utf8	12.41 KB	-rw-r--r--
server-wide.html.ja.utf8	12.02 KB	-rw-r--r--
server-wide.html.ko.euc-kr	10.41 KB	-rw-r--r--
server-wide.html.tr.utf8	12.4 KB	-rw-r--r--
sitemap.html	736 B	-rw-r--r--
sitemap.html.de	26.2 KB	-rw-r--r--
sitemap.html.en	25.95 KB	-rw-r--r--
sitemap.html.es	25.86 KB	-rw-r--r--
sitemap.html.fr.utf8	27.01 KB	-rw-r--r--
sitemap.html.ja.utf8	26.42 KB	-rw-r--r--
sitemap.html.ko.euc-kr	23.11 KB	-rw-r--r--
sitemap.html.tr.utf8	26.88 KB	-rw-r--r--
sitemap.html.zh-cn.utf8	23.98 KB	-rw-r--r--
socache.html	205 B	-rw-r--r--
socache.html.en	9.54 KB	-rw-r--r--
socache.html.fr.utf8	10.23 KB	-rw-r--r--
stopping.html	650 B	-rw-r--r--
stopping.html.de	19.53 KB	-rw-r--r--
stopping.html.en	17.4 KB	-rw-r--r--
stopping.html.es	19.32 KB	-rw-r--r--
stopping.html.fr.utf8	19.67 KB	-rw-r--r--
stopping.html.ja.utf8	19.98 KB	-rw-r--r--
stopping.html.ko.euc-kr	14.67 KB	-rw-r--r--
stopping.html.tr.utf8	19.55 KB	-rw-r--r--
suexec.html	464 B	-rw-r--r--
suexec.html.en	28.56 KB	-rw-r--r--
suexec.html.fr.utf8	32.24 KB	-rw-r--r--
suexec.html.ja.utf8	33.21 KB	-rw-r--r--
suexec.html.ko.euc-kr	24.09 KB	-rw-r--r--
suexec.html.tr.utf8	31.05 KB	-rw-r--r--
upgrading.html	209 B	-rw-r--r--
upgrading.html.en	29.98 KB	-rw-r--r--
upgrading.html.fr.utf8	33.4 KB	-rw-r--r--
urlmapping.html	484 B	-rw-r--r--
urlmapping.html.en	26.02 KB	-rw-r--r--
urlmapping.html.fr.utf8	28.39 KB	-rw-r--r--
urlmapping.html.ja.utf8	25.7 KB	-rw-r--r--
urlmapping.html.ko.euc-kr	19.33 KB	-rw-r--r--
urlmapping.html.tr.utf8	27.96 KB	-rw-r--r--

Code Editor : dns-caveats.html.en

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />

<title>Issues Regarding DNS and Apache HTTP Server - Apache HTTP Server Version 2.4</title>
<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
<link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="./style/css/prettify.css" />
<script src="./style/scripts/prettify.min.js" type="text/javascript">
</script>

<p>This page could be summarized with the statement: don't
    configure Apache HTTP Server in such a way that it relies on DNS resolution
    for parsing of the configuration files. If httpd requires DNS
    resolution to parse the configuration files then your server
    may be subject to reliability problems (ie. it might not start up),
    or denial and theft of service attacks (including virtual hosts able
    to steal hits from other virtual hosts).</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="#example">A Simple Example</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#denial">Denial of Service</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#main">The "main server" Address</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#tips">Tips to Avoid These Problems</a></li>
</ul><h3>See also</h3><ul class="seealso"><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="example" id="example">A Simple Example</a></h2>

<pre class="prettyprint lang-config"># This is a misconfiguration example, do not use on your server
&lt;VirtualHost www.example.dom&gt;
  ServerAdmin webgirl@example.dom
  DocumentRoot "/www/example"
&lt;/VirtualHost&gt;</pre>

<p>In order for the server to function properly, it absolutely needs
    to have two pieces of information about each virtual host: the
    <code class="directive"><a href="./mod/core.html#servername">ServerName</a></code> and at least one
    IP address that the server will bind and respond to. The above
    example does not include the IP address, so httpd must use DNS
    to find the address of <code>www.example.dom</code>. If for some
    reason DNS is not available at the time your server is parsing
    its config file, then this virtual host <strong>will not be
    configured</strong>. It won't be able to respond to any hits
    to this virtual host.</p>

<p>Suppose that <code>www.example.dom</code> has address 192.0.2.1.
    Then consider this configuration snippet:</p>

<pre class="prettyprint lang-config"># This is a misconfiguration example, do not use on your server
&lt;VirtualHost 192.0.2.1&gt;
  ServerAdmin webgirl@example.dom
  DocumentRoot "/www/example"
&lt;/VirtualHost&gt;</pre>

<p>This time httpd needs to use reverse DNS to find the
    <code>ServerName</code> for this virtualhost. If that reverse
    lookup fails then it will partially disable the virtualhost.
    If the virtual host is name-based then it will effectively be
    totally disabled, but if it is IP-based then it will mostly
    work. However, if httpd should ever have to generate a full
    URL for the server which includes the server name (such as when a
    Redirect is issued), then it will fail to generate a valid URL.</p>

<p>Here is a snippet that avoids both of these problems:</p>

<pre class="prettyprint lang-config">&lt;VirtualHost 192.0.2.1&gt;
  ServerName www.example.dom
  ServerAdmin webgirl@example.dom
  DocumentRoot "/www/example"
&lt;/VirtualHost&gt;</pre>

</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="denial" id="denial">Denial of Service</a></h2>

<p>Consider this configuration snippet:</p>

<pre class="prettyprint lang-config">&lt;VirtualHost www.example1.dom&gt;
  ServerAdmin webgirl@example1.dom
  DocumentRoot "/www/example1"
&lt;/VirtualHost&gt;
&lt;VirtualHost www.example2.dom&gt;
  ServerAdmin webguy@example2.dom
  DocumentRoot "/www/example2"
&lt;/VirtualHost&gt;</pre>

<p>Suppose that you've assigned 192.0.2.1 to
    <code>www.example1.dom</code> and 192.0.2.2 to
    <code>www.example2.dom</code>. Furthermore, suppose that
    <code>example1.dom</code> has control of their own DNS. With this
    config you have put <code>example1.dom</code> into a position where
    they can steal all traffic destined to <code>example2.dom</code>. To
    do so, all they have to do is set <code>www.example1.dom</code> to
    192.0.2.2. Since they control their own DNS you can't stop them
    from pointing the <code>www.example1.dom</code> record wherever they
    wish.</p>

<p>Requests coming in to 192.0.2.2 (including all those where
    users typed in URLs of the form
    <code>http://www.example2.dom/whatever</code>) will all be served by
    the <code>example1.dom</code> virtual host. To better understand why
    this happens requires a more in-depth discussion of how httpd
    matches up incoming requests with the virtual host that will
    serve it. A rough document describing this <a href="vhosts/details.html">is available</a>.</p>
  </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="main" id="main">The "main server" Address</a></h2>

<p><a href="vhosts/name-based.html">Name-based
    virtual host support</a> requires httpd to know
    the IP address(es) of the host that <code class="program"><a href="./programs/httpd.html">httpd</a></code>
    is running on. To get this address it uses either the global
    <code class="directive"><a href="./mod/core.html#servername">ServerName</a></code>
    (if present) or calls the C function <code>gethostname</code>
    (which should return the same as typing "hostname" at the
    command prompt). Then it performs a DNS lookup on this address.
    At present there is no way to avoid this lookup.</p>

<p>If you fear that this lookup might fail because your DNS
    server is down then you can insert the hostname in
    <code>/etc/hosts</code> (where you probably already have it so
    that the machine can boot properly). Then ensure that your
    machine is configured to use <code>/etc/hosts</code> in the
    event that DNS fails. Depending on what OS you are using this
    might be accomplished by editing <code>/etc/resolv.conf</code>,
    or maybe <code>/etc/nsswitch.conf</code>.</p>

<p>If your server doesn't have to perform DNS for any other
    reason then you might be able to get away with running httpd
    with the <code>HOSTRESORDER</code> environment variable set to
    "local". This all depends on what OS and resolver libraries you
    are using. It also affects CGIs unless you use
    <code class="module"><a href="./mod/mod_env.html">mod_env</a></code> to control the environment. It's best
    to consult the man pages or FAQs for your OS.</p>
  </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="tips" id="tips">Tips to Avoid These Problems</a></h2>

<ul>
      <li>
        use IP addresses in
        <code class="directive"><a href="./mod/core.html#virtualhost">VirtualHost</a></code>
      </li>

<li>
        use IP addresses in
        <code class="directive"><a href="./mod/mpm_common.html#listen">Listen</a></code>
      </li>

<li>
        ensure all virtual hosts have an explicit
        <code class="directive"><a href="./mod/core.html#servername">ServerName</a></code>
      </li>

<li>create a <code>&lt;VirtualHost _default_:*&gt;</code>
      server that has no pages to serve</li>
    </ul>
  </div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="./en/dns-caveats.html" title="English">&nbsp;en&nbsp;</a> |
<a href="./fr/dns-caveats.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
<a href="./ja/dns-caveats.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
<a href="./ko/dns-caveats.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
<a href="./tr/dns-caveats.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
</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&amp;A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed 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 Libera.chat, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div>
<script type="text/javascript"><![CDATA[//><!]]></script></div><div id="footer">
<p class="apache">Copyright 2023 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
<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></div><script type="text/javascript"><![CDATA[//><!]]></script>
</body></html>

${this.title}

Code Editor : dns-caveats.html.en