</code></p></div>
<p>Hosts whose names match, or end in, this string are allowed
access. Only complete components are matched, so the above
- example will match <code>foo.apache.org</code> but it will
- not match <code>fooapache.org</code>. This configuration will
- cause the server to perform a reverse DNS lookup on the
- client IP address, regardless of the setting of the <code class="directive"><a href="../mod/core.html#hostnamelookups">HostnameLookups</a></code>
- directive.</p></dd>
+ example will match <code>foo.apache.org</code> but it will not
+ match <code>fooapache.org</code>. This configuration will cause
+ Apache to perform a double reverse DNS lookup on the client IP
+ address, regardless of the setting of the <code class="directive"><a href="../mod/core.html#hostnamelookups">HostnameLookups</a></code> directive. It will do
+ a reverse DNS lookup on the IP address to find the associated
+ hostname, and then do a forward lookup on the hostname to assure
+ that it matches the original IP address. Only if the forward
+ and reverse DNS are consistent and the hostname matches will
+ access be allowed.</p></dd>
<dt>A full IP address</dt>
</example>
<p>Hosts whose names match, or end in, this string are allowed
access. Only complete components are matched, so the above
- example will match <code>foo.apache.org</code> but it will
- not match <code>fooapache.org</code>. This configuration will
- cause the server to perform a reverse DNS lookup on the
- client IP address, regardless of the setting of the <directive
- module="core">HostnameLookups</directive>
- directive.</p></dd>
+ example will match <code>foo.apache.org</code> but it will not
+ match <code>fooapache.org</code>. This configuration will cause
+ Apache to perform a double reverse DNS lookup on the client IP
+ address, regardless of the setting of the <directive
+ module="core">HostnameLookups</directive> directive. It will do
+ a reverse DNS lookup on the IP address to find the associated
+ hostname, and then do a forward lookup on the hostname to assure
+ that it matches the original IP address. Only if the forward
+ and reverse DNS are consistent and the hostname matches will
+ access be allowed.</p></dd>
<dt>A full IP address</dt>