grammar fixes

[apache] / docs / manual / mod / mod_proxy.xml

<?xml version="1.0"?>
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
<modulesynopsis metafile="mod_proxy.xml.meta">

<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>
      <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>

    <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
    <code>HTTP/1.1</code>, and filter support was enabled.</p>

    <p>During the overhaul process, <module>mod_proxy</module> features
    have been split into several module files: <module>mod_proxy_http</module>,
    <module>mod_proxy_ftp</module> and <module>mod_proxy_connect</module>.
    Thus, if you want to use one or more of the particular proxy functions,
    load <module>mod_proxy</module> <em>and</em> the appropriate
    module(s) into the server (either statically or dynamically via the
    <directive module="mod_so">LoadModule</directive> directive).</p>

    <p>Please note that the <strong>caching</strong> function present in <module
    >mod_proxy</module> up to Apache v1.3.x has been <strong>removed</strong>
    from <module>mod_proxy</module> and incorporated into a new module,
    <module>mod_cache</module>. In other words, the Apache 2.0.x proxy doesn't 
    cache - all caching functionality has been moved into
    <module>mod_cache</module>, which is capable of caching any content, not
    just content from the proxy.</p>

    <p>If you need to use SSL when contacting remote servers, have a look at the
    <code>SSLProxy*</code> directives in <module>mod_ssl</module>.</p>
</summary>
<seealso><module>mod_proxy_http</module></seealso>
<seealso><module>mod_proxy_ftp</module></seealso>
<seealso><module>mod_proxy_connect</module></seealso>
<seealso><module>mod_ssl</module></seealso>

<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="#mimetypes">Why doesn't file type <var>xxx</var> download via
    FTP?</a></li>
    <li><a href="#type">How can I force an FTP ASCII download of File
    <var>xxx</var>?</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 <dfn>forward</dfn> and
      <dfn>reverse</dfn> proxy configuration.</p>

      <p>A <dfn>forward proxy</dfn> 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 <module>mod_proxy</module> 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 <module>mod_cache</module>. Other dedicated
      forward proxy packages include <a href="http://www.squid-cache.org/"
      >Squid</a>.</p>

      <p>A <dfn>reverse proxy</dfn> 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
      <module>mod_proxy</module> 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> <!-- /forwardreverse -->

    <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 />
        <indent>
          Order Deny,Allow<br />
          Deny from all<br />
          Allow from 192.168.0<br />
        </indent>
        &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> <!-- /access -->

    <section id="mimetypes"><title>Why doesn't file type <var>xxx</var>
    download via FTP?</title>
      <p>You probably don't have that particular file type defined as
      <code>application/octet-stream</code> in your proxy's mime.types
      configuration file. A useful line can be</p>

      <example>
<pre>application/octet-stream   bin dms lha lzh exe class tgz taz</pre>
      </example>
    </section> <!-- /mimetypes -->

    <section id="type"><title>How can I force an FTP ASCII download of
    File <var>xxx</var>?</title>
      <p>In the rare situation where you must download a specific file using the
      FTP <code>ASCII</code> transfer method (while the default transfer is in
      <code>binary</code> mode), you can override <module>mod_proxy</module>'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> <!-- /type -->

    <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 <dfn>Squid
      %2f hack</dfn> was implemented in the Apache FTP proxy; it 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 <code>/%2f</code> to the path of your request, you can make
      such a proxy change the FTP starting directory to <code>/</code> (instead
      of the home directory). For example, to retrieve the file
      <code>/etc/motd</code>, you would use the URL:</p>

      <example>
        ftp://<var>user</var>@<var>host</var>/%2f/etc/motd
      </example>
    </section> <!-- /percent2fhck -->

    <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,
      <em>i.e.</em>,</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:</p>

      <example>
        ftp://<var>username</var>@<var>host</var>/myfile
      </example>

      <p>If the FTP server asks for a password when given this username (which
      it should), then Apache will reply with a <code>401</code> (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</p>

      <example>
        ftp://<var>username</var>:<var>password</var>@<var>host</var>/myfile
      </example>

      <p>in the first place).</p>

      <note><title>Note</title>
        <p>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.</p>
      </note>
    </section> <!-- /ftppass -->

    <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> <!-- /startup -->

    <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
      <code>http://somehost.example.com/</code>. 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> <!-- /intranet -->

    <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 <code>force-proxy-request-1.0</code> and
      <code>proxy-nokeepalive</code> notes.</p>

      <example>
        &lt;Location /buggyappserver/&gt;<br />
        <indent>
          ProxyPass http://buggyappserver:7001/foo/<br />
          SetEnv force-proxy-request-1.0 1<br />
          SetEnv proxy-nokeepalive 1<br />
        </indent>
        &lt;/Location&gt;
      </example>
    </section> <!-- /envsettings -->
</section>

<directivesynopsis type="section">
<name>Proxy</name>
<description>Container for directives applied to proxied resources</description>
<syntax>&lt;Proxy <var>wildcard-url</var>&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 />
      <indent>
        Order Deny,Allow<br />
        Deny from all<br />
        Allow from yournetwork.example.com<br />
      </indent>
      &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 />
      <indent>
        SetOutputFilter INCLUDES<br />
      </indent>
      &lt;/Proxy&gt;
    </example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>ProxyBadHeader</name>
<description>Determines how to handle bad header lines in a
response</description>
<syntax>ProxyBadHeader IsError|Ignore|StartBody</syntax>
<default>ProxyBadHeader IsError</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<compatibility>available in Apache 2.0.44 and later</compatibility>

<usage>
    <p>The <directive>ProxyBadHeader</directive> directive determines the
    behaviour of <module>mod_proxy</module> if it receives syntactically invalid
    header lines (<em>i.e.</em> containing no colon). The following arguments
    are possible:</p>

    <dl>
    <dt><code>IsError</code></dt>
    <dd>Abort the request and end up with a 502 (Bad Gateway) response. This is
    the default behaviour.</dd>

    <dt><code>Ignore</code></dt>
    <dd>Treat bad header lines as if they weren't sent.</dd>

    <dt><code>StartBody</code></dt>
    <dd>When receiving the first bad header line, finish reading the headers and
    treat the remainder as body. This helps to work around buggy backend servers
    which forget to insert an empty line between the headers and the body.</dd>
    </dl>
</usage>
</directivesynopsis>

<directivesynopsis type="section">
<name>ProxyMatch</name>
<description>Container for directives applied to regular-expression-matched 
proxied resources</description>
<syntax>&lt;ProxyMatch <var>regex</var>&gt; ...&lt;/ProxyMatch&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 <code>Off</code>. It is mostly 
    useful in special configurations like proxied mass name-based virtual
    hosting, where the original Host header needs to be evaluated by the
    backend server.</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 <code>Off</code> 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
    <code>Off</code>.</p>

    <p>In order to get the functionality of proxying HTTP or FTP sites, you
    need also <module>mod_proxy_http</module> or <module>mod_proxy_ftp</module>
    (or both) present in the server.</p>

    <note type="warning"><title>Warning</title>
      <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 <var>match</var> <var>remote-server</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>This defines remote proxies to this proxy. <var>match</var> 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 <code>*</code> to indicate
    the server should be contacted for all requests. <var>remote-server</var> is
    a partial URL for the remote server. Syntax:</p>

    <example>
      <dfn>remote-server</dfn> =
          <var>scheme</var>://<var>hostname</var>[:<var>port</var>]
    </example>

    <p><var>scheme</var> is effectively the protocol that should be used to
    communicate with the remote server; only <code>http</code> is supported by
    this module.</p>

    <example><title>Example</title>
      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>ProxyRemoteMatch <var>regex</var> <var>remote-server</var></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 [<var>path</var>] !|<var>url</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</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. <var>path</var> is the name of a local virtual path; <var>url</var>
    is a partial URL for the remote server and cannot include a query
    string.</p>

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

    <example>
      ProxyPass /mirror/foo/ http://backend.example.com/
    </example>

    <p>will cause a local request for
    <code>http://example.com/mirror/foo/bar</code> to be internally converted
    into a proxy request to <code>http://backend.example.com/bar</code>.</p>

    <p>The <code>!</code> directive is useful in situations where you don't want
    to reverse-proxy a subdirectory, <em>e.g.</em></p>

    <example>
      ProxyPass /mirror/foo/i !<br />
      ProxyPass /mirror/foo http://backend.example.com
    </example>

    <p>will proxy all requests to <code>/mirror/foo</code> to
    <code>backend.example.com</code> <em>except</em> requests made to
    <code>/mirror/foo/i</code>.</p>

    <note><title>Note</title>
      <p>Order is important. you need to put the exclusions <em>before</em> the
      general proxypass directive.</p>
    </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 [<var>path</var>] <var>url</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</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><var>path</var> is the name of a local virtual path. <var>url</var> 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>For example, suppose the local server has address
    <code>http://example.com/</code>; then</p>

    <example>
      ProxyPass         /mirror/foo/ http://backend.example.com/<br />
      ProxyPassReverse  /mirror/foo/ http://backend.example.com/
    </example>

    <p>will not only cause a local request for the
    <code>http://example.com/mirror/foo/bar</code> to be internally converted
    into a proxy request to <code>http://backend.example.com/bar</code>
    (the functionality <code>ProxyPass</code> provides here). It also takes care
    of redirects the server <code>backend.example.com</code> sends: when
    <code>http://backend.example.com/bar</code> is redirected by him to
    <code>http://backend.example.com/quux</code> Apache adjusts this to
    <code>http://example.com/mirror/foo/quux</code> before forwarding the HTTP
    redirect response to the client. Note that the hostname used for
    constructing the URL is chosen in respect to the setting of the <directive
    module="core">UseCanonicalName</directive> directive.</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 <var>port</var> [<var>port</var>] ...</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 <code>https</code>
    connection is requested and proxy tunneling over HTTP is in effect.</p>

    <p>By default, only the default https port (<code>443</code>) and the
    default snews port (<code>563</code>) are enabled. Use the
    <directive>AllowCONNECT</directive> directive to override this default and
    allow connections to the listed ports only.</p>

    <p>Note that you'll need to have <module>mod_proxy_connect</module> present
    in the server in order to get the support for the <code>CONNECT</code> at
    all.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>ProxyBlock</name>
<description>Words, hosts, or domains that are banned from being
proxied</description>
<syntax>ProxyBlock *|<var>word</var>|<var>host</var>|<var>domain</var>
[<var>word</var>|<var>host</var>|<var>domain</var>] ...</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. That may slow down the startup time of the server.</p>

    <example><title>Example</title>
      ProxyBlock joes-garage.com some-host.co.uk rocky.wotsamattau.edu
    </example>

    <p><code>rocky.wotsamattau.edu</code> would also be matched if referenced by
    IP address.</p>

    <p>Note that <code>wotsamattau</code> would also be sufficient to match
    <code>wotsamattau.edu</code>.</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 proxied HTTP and FTP
connections</description>
<syntax>ProxyReceiveBufferSize <var>bytes</var></syntax>
<default>ProxyReceiveBufferSize 0</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>The <directive>ProxyReceiveBufferSize</directive> directive specifies an
    explicit (TCP/IP) network buffer size for proxied HTTP and FTP connections,
    for increased throughput. It has to be greater than <code>512</code> or set
    to <code>0</code> 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>Determine size of internal data throughput buffer</description>
<syntax>ProxyIOBufferSize <var>bytes</var></syntax>
<default>ProxyIOBufferSize 8192</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>The <directive>ProxyIOBufferSize</directive> directive adjusts the size
    of the internal buffer, which is used as a scratchpad for the data between
    input and output. The size must be less or equal <code>8192</code>.</p>

    <p>In almost every case there's no reason to change that value.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>ProxyMaxForwards</name>
<description>Maximium number of proxies that a request can be forwarded
through</description>
<syntax>ProxyMaxForwards <var>number</var></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, if there's no
    <code>Max-Forwards</code> header supplied with the request. This is
    set to prevent infinite proxy loops, or a DoS attack.</p>

    <example><title>Example</title>
      ProxyMaxForwards 15
    </example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>NoProxy</name>
<description>Hosts, domains, or networks that will be connected to
directly</description>
<syntax>NoProxy <var>host</var> [<var>host</var>] ...</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 <var>host</var> arguments to the <directive>NoProxy</directive>
    directive are one of the following type list:</p>

    <dl>
    <!-- ===================== Domain ======================= -->
    <dt><var><a name="domain" id="domain">Domain</a></var></dt>
    <dd>
    <p>A <dfn>Domain</dfn> 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 <var>Domain</var>).</p>

    <example><title>Examples</title>
      .com .apache.org.
    </example>

    <p>To distinguish <var>Domain</var>s from <var><a href="#hostname"
    >Hostname</a></var>s (both syntactically and semantically; a DNS domain can
    have a DNS A record, too!), <var>Domain</var>s are always written with a
    leading period.</p>
    
    <note><title>Note</title>
      <p>Domain name comparisons are done without regard to the case, and
      <var>Domain</var>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.</p>
    </note></dd>

    <!-- ===================== SubNet ======================= -->
    <dt><var><a name="subnet" id="subnet">SubNet</a></var></dt>
    <dd>
    <p>A <dfn>SubNet</dfn> 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 <var>SubNet</var>. 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.) Examples:</p>

    <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>

    <p>As a degenerate case, a <em>SubNet</em> with 32 valid bits is the
    equivalent to an <var><a href="#ipadr">IPAddr</a></var>, while a <var>SubNet</var> with zero
    valid bits (<em>e.g.</em>, 0.0.0.0/0) is the same as the constant
    <var>_Default_</var>, matching any IP address.</p></dd>

    <!-- ===================== IPAddr ======================= -->
    <dt><var><a name="ipaddr" id="ipaddr">IPAddr</a></var></dt>
    <dd>
    <p>A <dfn>IPAddr</dfn> 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.</p>
    <example><title>Example</title>
      192.168.123.7
    </example>
    
    <note><title>Note</title>
      <p>An <var>IPAddr</var> does not need to be resolved by the DNS system, so
      it can result in more effective apache performance.</p>
    </note></dd>

    <!-- ===================== Hostname ======================= -->
    <dt><var><a name="hostname" id="hostname">Hostname</a></var></dt>
    <dd>
    <p>A <dfn>Hostname</dfn> is a fully qualified DNS domain name which can
    be resolved to one or more <var><a href="#ipaddr">IPAddrs</a></var> via the
    DNS domain name service. It represents a logical host (in contrast to
        <var><a href="#domain">Domain</a></var>s, see above) and must be resolvable
    to at least one <var><a href="#ipaddr">IPAddr</a></var> (or often to a list
    of hosts with different <var><a href="#ipaddr">IPAddr</a></var>s).</p>

    <example><title>Examples</title>
      prep.ai.mit.edu<br />
      www.apache.org
    </example>

    <note><title>Note</title>
      <p>In many situations, it is more effective to specify an <var><a
      href="#ipaddr">IPAddr</a></var> in place of a <var>Hostname</var> 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.</p>
      <p><var>Hostname</var> comparisons are done without regard to the case,
      and <var>Hostname</var>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.</p>
     </note></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 <var>seconds</var></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 useful 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 <var>Domain</var></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 <var>Domain</var> 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 <a
    href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> (HTTP/1.1), section
    14.45 for an explanation of <code>Via:</code> header lines.</p>

    <ul>
    <li>If set to <code>Off</code>, 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 <code>On</code>, each request and reply will get a
    <code>Via:</code> header line added for the current host.</li>

    <li>If set to <code>Full</code>, 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 <code>Block</code>, 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>