<?xml version="1.0"?>

<!DOCTYPE modulesynopsis SYSTEM "/style/modulesynopsis.dtd">

<?xml-stylesheet type="text/xsl" href="/style/manual.en.xsl"?>

<modulesynopsis>

<name>mod_proxy</name>

<description>HTTP/1.1 proxy/gateway server</description>

<status>Extension</status>

<sourcefile>mod_proxy.c</sourcefile>

<identifier>proxy_module</identifier>

<summary>

<note type="warning"><title>Warning</title>

This document has been updated to take into account changes

made in the 2.0 version of the Apache HTTP Server. Some of the

information may still be inaccurate, please use it

with care.

</note>

<p>This module implements a proxy/gateway for Apache. It implements

proxying capability for

<code>FTP</code>,

<code>CONNECT</code> (for SSL),

<code>HTTP/0.9</code>,

<code>HTTP/1.0</code>, and

<code>HTTP/1.1</code>.

The module can be configured to connect to other proxy modules for these

and other protocols.</p>

<p>This module was experimental in Apache 1.1.x. Improvements and bugfixes

were made in Apache v1.2.x and Apache v1.3.x, then the module underwent a major

overhaul for Apache v2.0. The protocol support was upgraded to HTTP/1.1,

and filter support was enabled.</p>

<p>Please note that the <strong>caching</strong> function present in

mod_proxy up to Apache v1.3.x has been <strong>removed</strong> from

mod_proxy and will be incorporated into a new module, mod_cache.</p>

<p>If you need to use SSL when contacting remote servers, have a look at the

<code>SSLProxy*</code> directives in mod_ssl.</p>

<note type="warning"><p>Do not enable proxying with <directive

module="mod_proxy">ProxyRequests</directive> until you have

<a href="#access">secured your server</a>. Open proxy servers are

dangerous both to your network and to the Internet at large.</p></note>

</summary>

<section id="configs"><title>Common configuration topics</title>

<ul>

<li><a href="#forwardreverse">Forward and Reverse Proxies</a></li>

<li><a href="#access">Controlling access to your proxy</a></li>

<li><a href="#shortname">Using Netscape hostname shortcuts</a></li>

<li><a href="#mimetypes">Why doesn't file type <em>xxx</em> download via FTP?</a></li>

<li><a href="#type">How can I force an FTP ASCII download of File <em>xxx</em>?</a></li>

<li><a href="#percent2fhack">How can I access FTP files outside of my home directory?</a></li>

<li><a href="#ftppass">How can I hide the FTP cleartext password in my browser's URL line?</a></li>

<li><a href="#startup">Why does Apache start more slowly when using the

proxy module?</a></li>

<li><a href="#intranet">What other functions are useful for an intranet proxy server?</a></li>

<li><a href="#envsettings">How can I make the proxy talk HTTP/1.0 and disable keepalives?</a></li>

</ul>

<section id="forwardreverse"><title>Forward and Reverse Proxies</title>

<p>Apache can be configured in both a <em>forward</em> and <em>reverse</em>

proxy configuration.</p>

<p>A <em>forward proxy</em> is an intermediate system that enables a browser to connect to a

remote network to which it normally does not have access. A forward proxy

can also be used to cache data, reducing load on the networks between the

forward proxy and the remote webserver.</p>

<p>Apache's mod_proxy can be figured to behave like a forward proxy

using the <directive module="mod_proxy">ProxyRemote</directive>

directive. In addition, caching of data can be achieved by configuring

Apache <module>mod_cache</module>. Other dedicated forward proxy

packages include <a href="http://www.squid.org">Squid</a>.</p>

<p>A <em>reverse proxy</em> is a webserver system that is capable of serving webpages

sourced from other webservers - in addition to webpages on disk or generated

dynamically by CGI - making these pages look like they originated at the

reverse proxy.</p>

<p>When configured with the mod_cache module the reverse

proxy can act as a cache for slower backend webservers. The reverse proxy

can also enable advanced URL strategies and management techniques, allowing

webpages served using different webserver systems or architectures to

coexist inside the same URL space. Reverse proxy systems are also ideal for

implementing centralised logging websites with many or diverse website

backends. Complex multi-tier webserver systems can be constructed using an

Apache mod_proxy frontend and any number of backend webservers.</p>

<p>The reverse proxy is configured using the

<directive module="mod_proxy">ProxyPass</directive> and <directive

module="mod_proxy">ProxyPassReverse</directive> directives. Caching can be

enabled using mod_cache as with the forward proxy.</p>

</section>

<section id="access"><title>Controlling access to your proxy</title>

<p>You can control who can access your proxy via the

<directive module="mod_proxy" type="section">Proxy</directive>

control block using the following example:</p>

<example>

&lt;Proxy *&gt;<br />

Order Deny,Allow<br />

Deny from all<br />

Allow from 192.168.0<br />

&lt;/Proxy&gt;

</example>

<p>When configuring a reverse proxy, access control takes on the

attributes of the normal server <directive module="core"

type="section">directory</directive> configuration.</p>

</section>

<section id="mimetypes"><title>Why doesn't file type <em>xxx</em>

download via FTP?</title>

<p>You probably don't have that particular file type defined as

<em>application/octet-stream</em> in your proxy's mime.types configuration

file. A useful line can be</p>

<example>

application/octet-stream bin dms lha lzh exe class tgz taz

</example>

</section>

<section id="type"><title>How can I force an FTP ASCII download of

File <em>xxx</em>?</title>

<p>In the rare situation where you must download a specific file using the FTP

<strong>ASCII</strong> transfer method (while the default transfer is in

<strong>binary</strong> mode), you can override mod_proxy's default by

suffixing the request with <code>;type=a</code> to force an ASCII transfer.

(FTP Directory listings are always executed in ASCII mode, however.)</p>

</section>

<section id="percent2fhck"><title>How can I access FTP files outside

of my home directory?</title>

<p>

An FTP URI is interpreted relative to the home directory of the user

who is logging in. Alas, to reach higher directory levels you cannot

use /../, as the dots are interpreted by the browser and not actually

sent to the FTP server. To address this problem, the so called "Squid

%2f hack" was implemented in the Apache FTP proxy; it is is a solution

which is also used by other popular proxy servers like the <a

href="http://www.squid-cache.org/">Squid Proxy Cache</a>. By

prepending /%2f to the path of your request, you can make such a proxy

change the FTP starting directory to / (instead of the home

directory). </p>

<p><strong>Example:</strong> To retrieve the file

<code>/etc/motd</code>, you would use the URL</p>

<example>ftp://<em>user@host</em>/%2f/etc/motd</example>

</section>

<section id="ftppass"><title>How can I hide the FTP cleartext password

in my browser's URL line?</title>

<p>

To log in to an FTP server by username and password, Apache

uses different strategies.

In absense of a user name and password in the URL altogether,

Apache sends an anomymous login to the FTP server, i.e.,</p>

<example>

user: anonymous<br />

password: apache_proxy@

</example>

<p>This works for all popular FTP servers which are configured for

anonymous access.</p>

<p>For a personal login with a specific username, you can embed

the user name into the URL, like in:

<code>ftp://<em>username@host</em>/myfile</code>. If the FTP server

asks for a password when given this username (which it should),

then Apache will reply with a [401 Authorization required] response,

which causes the Browser to pop up the username/password dialog.

Upon entering the password, the connection attempt is retried,

and if successful, the requested resource is presented.

The advantage of this procedure is that your browser does not

display the password in cleartext (which it would if you had used

<code>ftp://<em>username:password@host</em>/myfile</code> in

the first place).</p>

<note><title>Note</title>

The password which is transmitted in such a way

is not encrypted on its way. It travels between your browser and

the Apache proxy server in a base64-encoded cleartext string, and

between the Apache proxy and the FTP server as plaintext. You should

therefore think twice before accessing your FTP server via HTTP

(or before accessing your personal files via FTP at all!) When

using unsecure channels, an eavesdropper might intercept your

password on its way.

</note>

</section>

<section id="startup"><title>Why does Apache start more slowly when

using the proxy module?</title>

<p>If you're using the <directive module="mod_proxy">ProxyBlock</directive>

directive, hostnames' IP addresses are looked up and cached during

startup for later match test. This may take a few seconds (or more)

depending on the speed with which the hostname lookups occur.</p>

</section>

<section id="intranet"><title>What other functions are useful for an

intranet proxy server?</title>

<p>An Apache proxy server situated in an intranet needs to forward

external requests through the company's firewall. However, when it has

to access resources within the intranet, it can bypass the firewall

when accessing hosts. The <directive

module="mod_proxy">NoProxy</directive> directive is useful for

specifying which hosts belong to the intranet and should be accessed

directly.</p>

<p>Users within an intranet tend to omit the local domain name from their

WWW requests, thus requesting "http://somehost/" instead of

"http://somehost.my.dom.ain/". Some commercial proxy servers let them get

away with this and simply serve the request, implying a configured

local domain. When the <directive module="mod_proxy">ProxyDomain</directive> directive

is used and the server is <a href="#proxyrequests">configured for

proxy service</a>, Apache can return a redirect response and send the client

to the correct, fully qualified, server address. This is the preferred method

since the user's bookmark files will then contain fully qualified hosts.</p>

</section>

<section id="envsettings"><title>How can I make the proxy talk HTTP/1.0 and

disable keepalives?</title>

<p>For circumstances where you have a application server which doesn't implement

keepalives or HTTP/1.1 properly, there are 2 environment variables which when

set send a HTTP/1.0 with no keepalive. These are set via the <directive

module="mod_env">SetEnv</directive> directive.</p>

<p>These are the 'force-proxy-request-1.0' and 'proxy-nokeepalive' notes.</p>

<example>

&lt;location /buggyappserver/ &gt;<br />

ProxyPass http://buggyappserver:7001/foo/<br />

SetEnv force-proxy-request-1.0 1<br />

SetEnv proxy-nokeepalive 1<br />

&lt;/location&gt;

</example>

</section>

</section>

<directivesynopsis type="section">

<name>Proxy</name>

<description>Container for directives applied to proxied

resources</description>

<syntax>&lt;Proxy <em>wildcard-url</em>&gt; ...&lt;/Proxy&gt;</syntax>

<contextlist><context>server config</context>

<context>virtual host</context></contextlist>

<usage>

<p>Directives placed in <directive type="section">Proxy</directive>

sections apply only to matching proxied content. Shell-style

wildcards are allowed.</p>

<p>For example, the following will allow only hosts in

<code>yournetwork.example.com</code> to access content via your

proxy server:</p>

<example>

&lt;Proxy *&gt;<br />

&nbsp;&nbsp;Order Deny,Allow<br />

&nbsp;&nbsp;Deny from all<br />

&nbsp;&nbsp;Allow from yournetwork.example.com<br />

&lt;/Proxy&gt;

</example>

<p>The following example will process all files in the

<code>foo</code> directory of <code>example.com</code> through the

<code>INCLUDES</code> filter when they are sent through the proxy

server:</p>

<example>

&lt;Proxy http://example.com/foo/*&gt;<br />

&nbsp;&nbsp;SetOutputFilter INCLUDES<br />

&lt;/Proxy&gt;

</example>

</usage>

</directivesynopsis>

<directivesynopsis type="section">

<name>ProxyMatch</name>

<description>Container for directives applied to regular-expression-matched

proxied resources</description>

<syntax>&lt;Proxy <em>regex</em>&gt; ...&lt;/Proxy&gt;</syntax>

<contextlist><context>server config</context>

<context>virtual host</context></contextlist>

<usage>

<p>The <directive type="section">ProxyMatch</directive> directive is

identical to the <directive module="mod_proxy"

type="section">Proxy</directive> directive, except it matches URLs

using regular expressions.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyPreserveHost</name>

<description>Use incoming Host HTTP request header for

proxy request</description>

<syntax>ProxyPreserveHost on|off</syntax>

<default>ProxyPreserveHost Off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<compatibility>Available in

Apache 2.0.31 and later.</compatibility>

<usage>

<p>When enabled, this option will pass the Host: line from the

incoming request to the proxied host, instead of the hostname

specified in the proxypass line.

</p>

<p>This option should normally be turned 'off'.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyRequests</name>

<description>Enables forward (standard) proxy requests</description>

<syntax>ProxyRequests on|off</syntax>

<default>ProxyRequests Off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>This allows or prevents Apache from functioning as a forward proxy

server. (Setting ProxyRequests to 'off' does not disable use of the

<directive module="mod_proxy">ProxyPass</directive> directive.)</p>

<p>In a typical reverse proxy configuration, this option should be set to

'off'.</p>

<note type="warning"><p>Do not enable proxying with <directive

module="mod_proxy">ProxyRequests</directive> until you have

<a href="#access">secured your server</a>. Open proxy servers are

dangerous both to your network and to the Internet at large.</p></note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyRemote</name>

<description>Remote proxy used to handle certain requests</description>

<syntax>ProxyRemote <em>match remote-server</em></syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>This defines remote proxies to this proxy. <em>match</em> is either the

name of a URL-scheme that the remote server supports, or a partial URL

for which the remote server should be used, or '*' to indicate the

server should be contacted for all requests. <em>remote-server</em> is a

partial URL for the remote server. Syntax:</p>

<pre>

remote-server = protocol://hostname[:port]

</pre>

<p><em>protocol</em> is the protocol that should be used to communicate

with the remote server; only "http" is supported by this module.</p>

<p>

Example:</p>

<example>

ProxyRemote http://goodguys.com/ http://mirrorguys.com:8000<br />

ProxyRemote * http://cleversite.com<br />

ProxyRemote ftp http://ftpproxy.mydomain.com:8080

</example>

<p>In the last example, the proxy will forward FTP requests, encapsulated

as yet another HTTP proxy request, to another proxy which can handle

them.</p>

<p>This option also supports reverse proxy configuration - a backend

webserver can be embedded within a virtualhost URL space even if that

server is hidden by another forward proxy.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyRemoteMatch</name>

<description>Remote proxy used to handle requests

matched by regular expressions</description>

<syntax>ProxyRemote <em>regex remote-server</em></syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>ProxyRemoteMatch</directive> is identical

to the <directive module="mod_proxy">ProxyRemote</directive>

directive, except the first argument is a regular expression

match against the requested URL.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyPass</name>

<description>Maps remote servers into the local server

URL-space</description>

<syntax>ProxyPass [<em>path</em>] !|<em>url</em></syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>This directive allows remote servers to be mapped into the space of

the local server; the local server does not act as a proxy in the

conventional sense, but appears to be a mirror of the remote

server. <em>path</em> is the name of a local virtual path;

<em>url</em> is a partial URL for the remote server and cannot

include a query string.</p>

<p>Suppose the local server has address <code>http://wibble.org/</code>;

then</p>

<example>

ProxyPass /mirror/foo/ http://foo.com/

</example>

<p>will cause a local request for the

&lt;<code>http://wibble.org/mirror/foo/bar</code>&gt; to be

internally converted into a proxy request to

&lt;<code>http://foo.com/bar</code>&gt;.</p>

<p>

The ! directive is useful in situations where you don't want to reverse-proxy

a subdirectory. eg.</p>

<example>

ProxyPass /mirror/foo/i !<br />

ProxyPass /mirror/foo http://foo.com

</example>

<p>will proxy all requests to /mirror/foo to foo.com EXCEPT requests made to /mirror/foo/i</p>

<note>NB: order is important. you need to put the exclusions BEFORE the general proxypass directive</note>

<p>When used inside a <directive type="section"

module="core">Location</directive> section, the first argument is

ommitted and the local directory is obtained from the <directive

type="section" module="core">Location</directive>.</p>

<p>If you require a more flexible reverse-proxy configuration, see

the <directive module="mod_rewrite">RewriteRule</directive> directive

with the <code>[P]</code> flag.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyPassReverse</name>

<description>Adjusts the URL in HTTP response headers sent from

a reverse proxied server</description>

<syntax>ProxyPassReverse [<em>path</em>] <em>url</em></syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>This directive lets Apache adjust the URL in the <code>Location</code>,

<code>Content-Location</code> and <code>URI</code> headers on

HTTP redirect responses. This is essential when Apache is used as

a reverse proxy to avoid by-passing the reverse proxy because of HTTP

redirects on the backend servers which stay behind the reverse proxy.</p>

<p><em>path</em> is the name of a local virtual path.<br />

<em>url</em> is a partial URL for the remote server - the same way they are

used for the <directive module="mod_proxy">ProxyPass</directive> directive.</p>

<p>

Example:<br />

Suppose the local server has address <code>http://wibble.org/</code>; then</p>

<example>

ProxyPass /mirror/foo/ http://foo.com/<br />

ProxyPassReverse /mirror/foo/ http://foo.com/

</example>

<p>will not only cause a local request for the

&lt;<code>http://wibble.org/mirror/foo/bar</code>&gt; to be internally

converted into a proxy request to &lt;<code>http://foo.com/bar</code>&gt; (the

functionality <code>ProxyPass</code> provides here). It also takes care of

redirects the server foo.com sends: when <code>http://foo.com/bar</code> is

redirected by him to <code>http://foo.com/quux</code> Apache adjusts this to

<code>http://wibble.org/mirror/foo/quux</code> before forwarding the HTTP

redirect response to the client. </p>

<p>

Note that this <directive>ProxyPassReverse</directive> directive can

also be used in conjunction with the proxy pass-through feature

("<code>RewriteRule ... [P]</code>") from

<module>mod_rewrite</module> because its doesn't depend on a

corresponding <directive module="mod_proxy">ProxyPass</directive>

directive.</p>

<p>When used inside a <directive type="section"

module="core">Location</directive> section, the first argument is

ommitted and the local directory is obtained from the <directive

type="section" module="core">Location</directive>.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>AllowCONNECT</name>

<description>Ports that are allowed to <code>CONNECT</code> through

the proxy</description>

<syntax>AllowCONNECT <em>port</em> [<em>port</em>] ...</syntax>

<default>AllowCONNECT 443 563</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>AllowCONNECT</directive> directive specifies a list

of port numbers to which the proxy <code>CONNECT</code> method may

connect. Today's browsers use this method when a <em>https</em>

connection is requested and proxy tunneling over <em>http</em> is in

effect.<br /> By default, only the default https port (443) and the

default snews port (563) are enabled. Use the

<directive>AllowCONNECT</directive> directive to overrride this default and

allow connections to the listed ports only.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyBlock</name>

<description>Words, hosts, or domains that are banned from being

proxied</description>

<syntax>ProxyBlock *|<em>word|host|domain</em>

[<em>word|host|domain</em>] ...</syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>ProxyBlock</directive> directive specifies a list of

words, hosts and/or domains, separated by spaces. HTTP, HTTPS, and

FTP document requests to sites whose names contain matched words,

hosts or domains are <em>blocked</em> by the proxy server. The proxy

module will also attempt to determine IP addresses of list items which

may be hostnames during startup, and cache them for match test as

well. Example:</p>

<example>

ProxyBlock joes-garage.com some-host.co.uk rocky.wotsamattau.edu

</example>

<p>'rocky.wotsamattau.edu' would also be matched if referenced by IP

address.</p>

<p>Note that 'wotsamattau' would also be sufficient to match

'wotsamattau.edu'.</p>

<p>Note also that</p>

<example>

ProxyBlock *

</example>

<p>blocks connections to all sites.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyReceiveBufferSize</name>

<description>Network buffer size for outgoing HTTP and FTP

connections</description>

<syntax>ProxyReceiveBufferSize <em>bytes</em></syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>ProxyReceiveBufferSize</directive> directive

specifies an explicit network buffer size for outgoing HTTP and FTP

connections, for increased throughput. It has to be greater than 512

or set to 0 to indicate that the system's default buffer size should

be used.</p>

<example><title>Example</title>

ProxyReceiveBufferSize 2048

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyIOBufferSize</name>

<description>IO buffer size for outgoing HTTP and FTP

connections</description>

<syntax>ProxyIOBufferSize <em>bytes</em></syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyMaxForwards</name>

<description>Maximium number of proxies that a request can be forwarded

through</description>

<syntax>ProxyMaxForwards <em>number</em></syntax>

<default>ProxyMaxForwards 10</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<compatibility>Available in Apache 2.0 and later</compatibility>

<usage>

<p>The <directive>ProxyMaxForwards</directive> directive specifies the

maximum number of proxies through which a request may pass. This is

set to prevent infinite proxy loops, or a DoS attack.</p>

<example><title>Example</title>

ProxyMaxForwards 10

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>NoProxy</name>

<description>Hosts, domains, or networks that will be connected

to directly</description>

<syntax>NoProxy <em>host</em> [<em>host</em>] ...</syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>This directive is only useful for Apache proxy servers within

intranets. The <directive>NoProxy</directive> directive specifies a

list of subnets, IP addresses, hosts and/or domains, separated by

spaces. A request to a host which matches one or more of these is

always served directly, without forwarding to the configured

<directive module="mod_proxy">ProxyRemote</directive> proxy server(s).</p>

<example><title>Example</title>

ProxyRemote * http://firewall.mycompany.com:81<br />

NoProxy .mycompany.com 192.168.112.0/21

</example>

<p>The <em>host</em> arguments to the NoProxy directive are one of the

following type list:</p>

<dl>

<!-- ===================== Domain ======================= -->

<dt><a name="domain">

<em>Domain</em></a></dt>

<dd>A <em>Domain</em> is a partially qualified DNS domain name, preceded

by a period.

It represents a list of hosts which logically belong to the same DNS

domain or zone (<em>i.e.</em>, the suffixes of the hostnames are all ending in

<em>Domain</em>).<br />

Examples: <code>.com</code> <code>.apache.org.</code><br />

To distinguish <em>Domain</em>s from <a href="#hostname"><em>Hostname</em></a>s (both

syntactically and semantically; a DNS domain can have a DNS A record,

too!), <em>Domain</em>s are always written

with a leading period.<br />

Note: Domain name comparisons are done without regard to the case,

and <em>Domain</em>s are always assumed to be anchored in the root

of the DNS tree, therefore two domains <code>.MyDomain.com</code> and

<code>.mydomain.com.</code> (note the trailing period) are

considered equal. Since a domain comparison does not involve a DNS

lookup, it is much more efficient than subnet comparison.</dd>

<!-- ===================== SubNet ======================= -->

<dt><a name="subnet">

<em>SubNet</em></a></dt>

<dd>A <em>SubNet</em> is a partially qualified internet address in

numeric (dotted quad) form, optionally followed by a slash and the

netmask, specified as the number of significant bits in the

<em>SubNet</em>. It is used to represent a subnet of hosts which can

be reached over a common network interface. In the absence of the

explicit net mask it is assumed that omitted (or zero valued)

trailing digits specify the mask. (In this case, the netmask can

only be multiples of 8 bits wide.)<br />

Examples:

<dl>

<dt><code>192.168</code> or <code>192.168.0.0</code></dt>

<dd>the subnet 192.168.0.0 with an implied netmask of 16 valid bits

(sometimes used in the netmask form <code>255.255.0.0</code>)</dd>

<dt><code>192.168.112.0/21</code></dt>

<dd>the subnet <code>192.168.112.0/21</code> with a netmask of 21

valid bits (also used in the form 255.255.248.0)</dd>

</dl>

As a degenerate case, a <em>SubNet</em> with 32 valid bits is the

equivalent to an <em>IPAddr</em>, while a <em>SubNet</em> with zero

valid bits (<em>e.g.</em>, 0.0.0.0/0) is the same as the constant

<em>_Default_</em>, matching any IP address. </dd>

<!-- ===================== IPAddr ======================= -->

<dt><a name="ipaddr">

<em>IPAddr</em></a></dt>

<dd>A <em>IPAddr</em> represents a fully qualified internet address in

numeric (dotted quad) form. Usually, this address represents a

host, but there need not necessarily be a DNS domain name

connected with the address.<br />

Example: 192.168.123.7<br />

Note: An <em>IPAddr</em> does not need to be resolved by the DNS

system, so it can result in more effective apache performance.</dd>

<!-- ===================== Hostname ======================= -->

<dt><a name="hostname">

<em>Hostname</em></a></dt>

<dd>A <em>Hostname</em> is a fully qualified DNS domain name which can

be resolved to one or more <a

href="#ipaddr"><em>IPAddrs</em></a> via the DNS domain name service.

It represents a logical host (in contrast to

<a href="#domain"><em>Domain</em></a>s, see

above) and must be resolvable to at least one <a

href="#ipaddr"><em>IPAddr</em></a> (or often to a list of hosts

with different <a href="#ipaddr"><em>IPAddr</em></a>'s).<br />

Examples: <code>prep.ai.mit.edu</code>

<code>www.apache.org.</code><br />

Note: In many situations, it is more effective to specify an

<a href="#ipaddr"><em>IPAddr</em></a> in place of a

<em>Hostname</em> since a DNS lookup

can be avoided. Name resolution in Apache can take a remarkable deal

of time when the connection to the name server uses a slow PPP

link.<br />

Note: <em>Hostname</em> comparisons are done without regard to the case,

and <em>Hostname</em>s are always assumed to be anchored in the root

of the DNS tree, therefore two hosts <code>WWW.MyDomain.com</code>

and <code>www.mydomain.com.</code> (note the trailing period) are

considered equal.</dd>

</dl>

</usage>

<seealso><a href="/dns-caveats.html">DNS Issues</a></seealso>

</directivesynopsis>

<directivesynopsis>

<name>ProxyTimeout</name>

<description>Network timeout for proxied requests</description>

<syntax>ProxyTimeout <em>seconds</em></syntax>

<default>ProxyTimeout 300</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<compatibility>Available in

Apache 2.0.31 and later</compatibility>

<usage>

<p>This directive allows a user to specifiy a timeout on proxy requests.

This is usefull when you have a slow/buggy appserver which hangs,

and you would rather just return a timeout and fail gracefully instead

of waiting however long it takes the server to return

</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyDomain</name>

<description>Default domain name for proxied requests</description>

<syntax>ProxyDomain <em>Domain</em></syntax>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>This directive is only useful for Apache proxy servers within

intranets. The <directive>ProxyDomain</directive> directive specifies

the default domain which the apache proxy server will belong to. If a

request to a host without a domain name is encountered, a redirection

response to the same host with the configured <em>Domain</em> appended

will be generated.</p>

<example><title>Example</title>

ProxyRemote * http://firewall.mycompany.com:81<br />

NoProxy .mycompany.com 192.168.112.0/21<br />

ProxyDomain .mycompany.com

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyVia</name>

<description>Information provided in the <code>Via</code> HTTP response

header for proxied requests</description>

<syntax>ProxyVia on|off|full|block</syntax>

<default>ProxyVia off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<usage>

<p>This directive controls the use of the <code>Via:</code> HTTP

header by the proxy. Its intended use is to control the flow of of

proxy requests along a chain of proxy servers. See RFC2068 (HTTP/1.1)

for an explanation of <code>Via:</code> header lines.</p>

<ul> <li>If set

to <em>off</em>, which is the default, no special processing is

performed. If a request or reply contains a <code>Via:</code> header,

it is passed through unchanged.</li>

<li>If set to <em>on</em>, each

request and reply will get a <code>Via:</code> header line added for

the current host.</li>

<li>If set to <em>full</em>, each generated <code>Via:</code> header

line will additionally have the Apache server version shown as a

<code>Via:</code> comment field.</li>

<li>If set to <em>block</em>, every

proxy request will have all its <code>Via:</code> header lines

removed. No new <code>Via:</code> header will be generated.</li>

</ul>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ProxyErrorOverride</name>

<description>Override error pages for proxied content</description>

<syntax>ProxyErrorOverride On|Off</syntax>

<default>ProxyErrorOverride Off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<compatibility>Available in version 2.0 and later</compatibility>

<usage>

<p>This directive is useful for reverse-proxy setups, where you want to

have a common look and feel on the error pages seen by the end user.

This also allows for included files (via mod_include's SSI) to get

the error code and act accordingly (default behavior would display

the error page of the proxied server, turning this on shows the SSI

Error message).</p>

</usage>

</directivesynopsis>

</modulesynopsis>