Remove these Pre-1.3 vhost files from the 2.0 docs. (748b3cc8) · Commits · CYBER - Cyber Security / TS 103 523 MSP / TLMSP / TLMSP Apache Httpd

docs/manual/vhosts/host.html

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		<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
		<HTML><HEAD>
		<TITLE>Apache non-IP Virtual Hosts</TITLE>
		</HEAD>

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		<!--#include virtual="header.html" -->
		<H1 ALIGN="CENTER">Apache non-IP Virtual Hosts</H1>

		<STRONG>See Also:</STRONG>
		<A HREF="virtual-host.html">Virtual Host Support</A>

		<HR>

		<H2>What is a Virtual Host</H2>

		<P>The "Virtual Host" refers to the practice of maintaining more than
		one server on one machine, as differentiated by their apparent
		hostname. For example, it is often desirable for companies sharing a
		web server to have their own domains, with web servers accessible as
		<CODE>www.company1.com</CODE> and <CODE>www.company2.com</CODE>,
		without requiring the user to know any extra path information.</P>

		<P>Apache was one of the first servers to support virtual hosts right
		out of the box, but since the base <CODE>HTTP</CODE> (HyperText
		Transport Protocol) standard does not allow any method for the server
		to determine the hostname it is being addressed as, Apache's virtual
		host support has required a separate IP address for each
		server. Documentation on using this approach (which still works very
		well) <A HREF="virtual-host.html">is available</A>.

		<P>While the approach described above works, with the available IP
		address space growing smaller, and the number of domains increasing,
		it is not the most elegant solution, and is hard to implement on some
		machines. The <CODE>HTTP/1.1</CODE> protocol contains a method for the
		server to identify what name it is being addressed as. Apache 1.1 and
		later support this approach as well as the traditional
		IP-address-per-hostname method.</P>

		<P>The benefits of using the new virtual host support is a practically
		unlimited number of servers, ease of configuration and use, and
		requires no additional hardware or software. The main disadvantage is
		that the user's browser must support this part of the protocol. The
		latest versions of many browsers (including Netscape Navigator 2.0 and
		later) do, but many browsers, especially older ones, do not. This can
		cause problems, although a possible solution is addressed below.</P>

		<H2>Using non-IP Virtual Hosts</H2>

		<P>Using the new virtual hosts is quite easy, and superficially looks
		like the old method. You simply add to one of the Apache configuration
		files (most likely <CODE>httpd.conf</CODE> or <CODE>srm.conf</CODE>)
		code similar to the following:</P>
		<PRE>
		<VirtualHost www.apache.org>
		ServerName www.apache.org
		DocumentRoot /usr/web/apache
		</VirtualHost>
		</PRE>

		<P>Of course, any additional directives can (and should) be placed
		into the <CODE><VirtualHost></CODE> section. To make this work,
		all that is needed is to make sure that the <CODE>www.apache.org</CODE>
		DNS entry points to the same IP address as the main
		server. Optionally, you could simply use that IP address in the
		<VirtualHost> entry.</P>

		<P>Additionally, many servers may wish to be accessible by more than
		one name. For example, the Apache server might want to be accessible
		as <CODE>apache.org</CODE>, or <CODE>ftp.apache.org</CODE>, assuming
		the IP addresses pointed to the same server. In fact, one might want it
		so that all addresses at <CODE>apache.org</CODE> were picked up by the
		server. This is possible with the <CODE>ServerAlias</CODE>
		directive, placed inside the <VirtualHost> section. For
		example:</P>

		<PRE>
		ServerAlias apache.org *.apache.org
		</PRE>

		<P>Note that you can use <CODE>*</CODE> and <CODE>?</CODE> as wild-card
		characters.</P>

		<P>You also might need ServerAlias if you are serving local users who
		do not always include the domain name. For example, if local users are
		familiar with typing "www" or "www.physics" then you will need to add
		<CODE>ServerAlias www www.physics</CODE>. It isn't possible for the
		server to know what domain the client uses for their name resolution
		because the client doesn't provide that information in the request.</P>

		<H2>Security Considerations</H2>

		Apache allows all virtual hosts to be made accessible via the
		<CODE>Host:</CODE> header through all IP interfaces, even those which
		are configured to use different IP interfaces. For example, if the
		configuration for <CODE>www.foo.com</CODE> contained a virtual host
		section for <CODE>www.bar.com</CODE>, and <CODE>www.bar.com</CODE> was
		a separate IP interface, such that
		non-<CODE>Host:</CODE>-header-supporting browsers can use it, as
		before with Apache 1.0. If a request is made to
		<CODE>www.foo.com</CODE> and the request includes the header
		<CODE>Host: www.bar.com</CODE>, a page from <CODE>www.bar.com</CODE>
		will be sent.

		<P>

		This is a security concern if you are controlling access to a
		particular server based on IP-layer controls, such as from within a
		firewall or router. Let's say <CODE>www.bar.com</CODE> in the above
		example was instead an intra-net server called
		<CODE>private.foo.com</CODE>, and the router used by foo.com only let
		internal users access <CODE>private.foo.com</CODE>. Obviously,
		<CODE>Host:</CODE> header functionality now allows someone who has
		access to <CODE>www.foo.com</CODE> to get
		<CODE>private.foo.com</CODE>, if they send a <CODE>Host:
		private.foo.com</CODE> header. It is important to note that this
		condition exists only if you only implement this policy at the IP
		layer - all security controls used by Apache (<EM>i.e.</EM>, <A
		HREF="../mod/mod_access.html">Allow, Deny from,</A> <EM>etc.</EM>) are
		consistently respected.

		<H2>Compatibility with Older Browsers</H2>

		<P>As mentioned earlier, a majority of browsers do not send the
		required data for the new virtual hosts to work properly. These
		browsers will always be sent to the main server's pages. There is a
		workaround, albeit a slightly cumbersome one:</P>

		<P>To continue the <CODE>www.apache.org</CODE> example (Note: Apache's
		web server does not actually function in this manner), we might use the
		new <CODE>ServerPath</CODE> directive in the <CODE>www.apache.org</CODE>
		virtual host, for example:

		<PRE>
		ServerPath /apache
		</PRE>
		<P>What does this mean? It means that a request for any file beginning
		with "<CODE>/apache</CODE>" will be looked for in the Apache
		docs. This means that the pages can be accessed as
		<CODE>http://www.apache.org/apache/</CODE> for all browsers, although
		new browsers can also access it as
		<CODE>http://www.apache.org/</CODE>.</P>

		<P>In order to make this work, put a link on your main server's page
		to <CODE>http://www.apache.org/apache/</CODE> (Note: Do not use
		<CODE>http://www.apache.org/</CODE> - this would create an endless
		loop). Then, in the virtual host's pages, be sure to use either purely
		relative links (<EM>e.g.</EM>, "<CODE>file.html</CODE>" or
		"<CODE>../icons/image.gif</CODE>" or links containing the prefacing
		<CODE>/apache/</CODE>
		(<EM>e.g.</EM>, "<CODE>http://www.apache.org/apache/file.html</CODE>" or
		"<CODE>/apache/docs/1.1/index.html</CODE>").</P>

		<P>This requires a bit of
		discipline, but adherence to these guidelines will, for the most part,
		ensure that your pages will work with all browsers, new and old. When
		a new browser contacts <CODE>http://www.apache.org/</CODE>, they will
		be directly taken to the Apache pages. Older browsers will be able to
		click on the link from the main server, go to
		<CODE>http://www.apache.org/apache/</CODE>, and then access the
		pages.</P>

		<!--#include virtual="footer.html" -->
		</BODY>
		</HTML>

docs/manual/vhosts/vhosts-in-depth.html

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		<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
		<HTML><HEAD>
		<TITLE>An In-Depth Discussion of VirtualHost Matching</TITLE>
		</HEAD>

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		ALINK="#FF0000"
		>
		<!--#include virtual="header.html" -->
		<H1 ALIGN="CENTER">An In-Depth Discussion of VirtualHost Matching</H1>

		<P>This is a very rough document that was probably out of date the moment
		it was written. It attempts to explain exactly what the code does when
		deciding what virtual host to serve a hit from. It's provided on the
		assumption that something is better than nothing. The server version
		under discussion is Apache 1.2.

		<P>If you just want to "make it work" without understanding
		how, there's a <A HREF="#whatworks">What Works</A> section at the bottom.

		<H3>Config File Parsing</H3>

		<P>There is a main_server which consists of all the definitions appearing
		outside of <CODE>VirtualHost</CODE> sections. There are virtual servers,
		called <EM>vhosts</EM>, which are defined by
		<A
		HREF="../mod/core.html#virtualhost"
		><SAMP>VirtualHost</SAMP></A>
		sections.

		<P>The directives
		<A
		HREF="../mod/core.html#port"
		><SAMP>Port</SAMP></A>,
		<A
		HREF="../mod/core.html#servername"
		><SAMP>ServerName</SAMP></A>,
		<A
		HREF="../mod/core.html#serverpath"
		><SAMP>ServerPath</SAMP></A>,
		and
		<A
		HREF="../mod/core.html#serveralias"
		><SAMP>ServerAlias</SAMP></A>
		can appear anywhere within the definition of
		a server. However, each appearance overrides the previous appearance
		(within that server).

		<P>The default value of the <CODE>Port</CODE> field for main_server
		is 80. The main_server has no default <CODE>ServerName</CODE>,
		<CODE>ServerPath</CODE>, or <CODE>ServerAlias</CODE>.

		<P>In the absence of any
		<A
		HREF="../mod/core.html#listen"
		><SAMP>Listen</SAMP></A>
		directives, the (final if there
		are multiple) <CODE>Port</CODE> directive in the main_server indicates
		which port httpd will listen on.

		<P> The <CODE>Port</CODE> and <CODE>ServerName</CODE> directives for
		any server main or virtual are used when generating URLs such as during
		redirects.

		<P> Each address appearing in the <CODE>VirtualHost</CODE> directive
		can have an optional port. If the port is unspecified it defaults to
		the value of the main_server's most recent <CODE>Port</CODE> statement.
		The special port <SAMP>*</SAMP> indicates a wildcard that matches any port.
		Collectively the entire set of addresses (including multiple
		<SAMP>A</SAMP> record
		results from DNS lookups) are called the vhost's <EM>address set</EM>.

		<P> The magic <CODE>_default_</CODE> address has significance during
		the matching algorithm. It essentially matches any unspecified address.

		<P> After parsing the <CODE>VirtualHost</CODE> directive, the vhost server
		is given a default <CODE>Port</CODE> equal to the port assigned to the
		first name in its <CODE>VirtualHost</CODE> directive. The complete
		list of names in the <CODE>VirtualHost</CODE> directive are treated
		just like a <CODE>ServerAlias</CODE> (but are not overridden by any
		<CODE>ServerAlias</CODE> statement). Note that subsequent <CODE>Port</CODE>
		statements for this vhost will not affect the ports assigned in the
		address set.

		<P>
		All vhosts are stored in a list which is in the reverse order that
		they appeared in the config file. For example, if the config file is:

		<BLOCKQUOTE><PRE>
		<VirtualHost A>
		...
		</VirtualHost>

		<VirtualHost B>
		...
		</VirtualHost>

		<VirtualHost C>
		...
		</VirtualHost>
		</PRE></BLOCKQUOTE>

		Then the list will be ordered: main_server, C, B, A. Keep this in mind.

		<P>
		After parsing has completed, the list of servers is scanned, and various
		merges and default values are set. In particular:

		<OL>
		<LI>If a vhost has no
		<A
		HREF="../mod/core.html#serveradmin"
		><CODE>ServerAdmin</CODE></A>,
		<A
		HREF="../mod/core.html#resourceconfig"
		><CODE>ResourceConfig</CODE></A>,
		<A
		HREF="../mod/core.html#accessconfig"
		><CODE>AccessConfig</CODE></A>,
		<A
		HREF="../mod/core.html#timeout"
		><CODE>Timeout</CODE></A>,
		<A
		HREF="../mod/core.html#keepalivetimeout"
		><CODE>KeepAliveTimeout</CODE></A>,
		<A
		HREF="../mod/core.html#keepalive"
		><CODE>KeepAlive</CODE></A>,
		<A
		HREF="../mod/core.html#maxkeepaliverequests"
		><CODE>MaxKeepAliveRequests</CODE></A>,
		or
		<A
		HREF="../mod/core.html#sendbuffersize"
		><CODE>SendBufferSize</CODE></A>
		directive then the respective value is
		inherited from the main_server. (That is, inherited from whatever
		the final setting of that value is in the main_server.)

		<LI>The "lookup defaults" that define the default directory
		permissions
		for a vhost are merged with those of the main server. This includes
		any per-directory configuration information for any module.

		<LI>The per-server configs for each module from the main_server are
		merged into the vhost server.
		</OL>

		Essentially, the main_server is treated as "defaults" or a
		"base" on
		which to build each vhost. But the positioning of these main_server
		definitions in the config file is largely irrelevant -- the entire
		config of the main_server has been parsed when this final merging occurs.
		So even if a main_server definition appears after a vhost definition
		it might affect the vhost definition.

		<P> If the main_server has no <CODE>ServerName</CODE> at this point,
		then the hostname of the machine that httpd is running on is used
		instead. We will call the <EM>main_server address set</EM> those IP
		addresses returned by a DNS lookup on the <CODE>ServerName</CODE> of
		the main_server.

		<P> Now a pass is made through the vhosts to fill in any missing
		<CODE>ServerName</CODE> fields and to classify the vhost as either
		an <EM>IP-based</EM> vhost or a <EM>name-based</EM> vhost. A vhost is
		considered a name-based vhost if any of its address set overlaps the
		main_server (the port associated with each address must match the
		main_server's <CODE>Port</CODE>). Otherwise it is considered an IP-based
		vhost.

		<P> For any undefined <CODE>ServerName</CODE> fields, a name-based vhost
		defaults to the address given first in the <CODE>VirtualHost</CODE>
		statement defining the vhost. Any vhost that includes the magic
		<SAMP>_default_</SAMP> wildcard is given the same <CODE>ServerName</CODE> as
		the main_server. Otherwise the vhost (which is necessarily an IP-based
		vhost) is given a <CODE>ServerName</CODE> based on the result of a reverse
		DNS lookup on the first address given in the <CODE>VirtualHost</CODE>
		statement.

		<P>

		<H3>Vhost Matching</H3>


		<P><STRONG>Apache 1.3 differs from what is documented
		here, and documentation still has to be written.</STRONG>

		<P>
		The server determines which vhost to use for a request as follows:

		<P> <CODE>find_virtual_server</CODE>: When the connection is first made
		by the client, the local IP address (the IP address to which the client
		connected) is looked up in the server list. A vhost is matched if it
		is an IP-based vhost, the IP address matches and the port matches
		(taking into account wildcards).

		<P> If no vhosts are matched then the last occurrence, if it appears,
		of a <SAMP>_default_</SAMP> address (which if you recall the ordering of the
		server list mentioned above means that this would be the first occurrence
		of <SAMP>_default_</SAMP> in the config file) is matched.

		<P> In any event, if nothing above has matched, then the main_server is
		matched.

		<P> The vhost resulting from the above search is stored with data
		about the connection. We'll call this the <EM>connection vhost</EM>.
		The connection vhost is constant over all requests in a particular TCP/IP
		session -- that is, over all requests in a KeepAlive/persistent session.

		<P> For each request made on the connection the following sequence of
		events further determines the actual vhost that will be used to serve
		the request.

		<P> <CODE>check_fulluri</CODE>: If the requestURI is an absoluteURI, that
		is it includes <CODE>http://hostname/</CODE>, then an attempt is made to
		determine if the hostname's address (and optional port) match that of
		the connection vhost. If it does then the hostname portion of the URI
		is saved as the <EM>request_hostname</EM>. If it does not match, then the
		URI remains untouched. <STRONG>Note</STRONG>: to achieve this address
		comparison,
		the hostname supplied goes through a DNS lookup unless it matches the
		<CODE>ServerName</CODE> or the local IP address of the client's socket.

		<P> <CODE>parse_uri</CODE>: If the URI begins with a protocol
		(<EM>i.e.</EM>, <CODE>http:</CODE>, <CODE>ftp:</CODE>) then the request is
		considered a proxy request. Note that even though we may have stripped
		an <CODE>http://hostname/</CODE> in the previous step, this could still
		be a proxy request.

		<P> <CODE>read_request</CODE>: If the request does not have a hostname
		from the earlier step, then any <CODE>Host:</CODE> header sent by the
		client is used as the request hostname.

		<P> <CODE>check_hostalias</CODE>: If the request now has a hostname,
		then an attempt is made to match for this hostname. The first step
		of this match is to compare any port, if one was given in the request,
		against the <CODE>Port</CODE> field of the connection vhost. If there's
		a mismatch then the vhost used for the request is the connection vhost.
		(This is a bug, see observations.)

		<P>
		If the port matches, then httpd scans the list of vhosts starting with
		the next server <STRONG>after</STRONG> the connection vhost. This scan does not
		stop if there are any matches, it goes through all possible vhosts,
		and in the end uses the last match it found. The comparisons performed
		are as follows:

		<UL>
		<LI>Compare the request hostname:port with the vhost
		<CODE>ServerName</CODE> and <CODE>Port</CODE>.

		<LI>Compare the request hostname against any and all addresses given in
		the <CODE>VirtualHost</CODE> directive for this vhost.

		<LI>Compare the request hostname against the <CODE>ServerAlias</CODE>
		given for the vhost.
		</UL>

		<P>
		<CODE>check_serverpath</CODE>: If the request has no hostname
		(back up a few paragraphs) then a scan similar to the one
		in <CODE>check_hostalias</CODE> is performed to match any
		<CODE>ServerPath</CODE> directives given in the vhosts. Note that the
		<STRONG>last match</STRONG> is used regardless (again consider the ordering of
		the virtual hosts).

		<H3>Observations</H3>

		<UL>

		<LI>It is difficult to define an IP-based vhost for the machine's
		"main IP address". You essentially have to create a bogus
		<CODE>ServerName</CODE> for the main_server that does not match the
		machine's IPs.
		<P>

		<LI>During the scans in both <CODE>check_hostalias</CODE> and
		<CODE>check_serverpath</CODE> no check is made that the vhost being
		scanned is actually a name-based vhost. This means, for example, that
		it's possible to match an IP-based vhost through another address. But
		because the scan starts in the vhost list at the first vhost that
		matched the local IP address of the connection, not all IP-based vhosts
		can be matched.
		<P>
		Consider the config file above with three vhosts A, B, C. Suppose
		that B is a named-based vhost, and A and C are IP-based vhosts. If
		a request comes in on B or C's address containing a header
		"<SAMP>Host: A</SAMP>" then
		it will be served from A's config. If a request comes in on A's
		address then it will always be served from A's config regardless of
		any Host: header.
		</P>

		<LI>Unless you have a <SAMP>_default_</SAMP> vhost,
		it doesn't matter if you mix name-based vhosts in amongst IP-based
		vhosts. During the <CODE>find_virtual_server</CODE> phase above no
		named-based vhost will be matched, so the main_server will remain the
		connection vhost. Then scans will cover all vhosts in the vhost list.
		<P>
		If you do have a <SAMP>_default_</SAMP> vhost, then you cannot place
		named-based vhosts after it in the config. This is because on any
		connection to the main server IPs the connection vhost will always be
		the <SAMP>_default_</SAMP> vhost since none of the name-based are
		considered during <CODE>find_virtual_server</CODE>.
		</P>

		<LI>You should never specify DNS names in <CODE>VirtualHost</CODE>
		directives because it will force your server to rely on DNS to boot.
		Furthermore it poses a security threat if you do not control the
		DNS for all the domains listed.
		<A HREF="dns-caveats.html">There's more information
		available on this and the next two topics</A>.
		<P>

		<LI><CODE>ServerName</CODE> should always be set for each vhost. Otherwise
		A DNS lookup is required for each vhost.
		<P>

		<LI>A DNS lookup is always required for the main_server's
		<CODE>ServerName</CODE> (or to generate that if it isn't specified
		in the config).
		<P>

		<LI>If a <CODE>ServerPath</CODE> directive exists which is a prefix of
		another <CODE>ServerPath</CODE> directive that appears later in
		the configuration file, then the former will always be matched
		and the latter will never be matched. (That is assuming that no
		Host header was available to disambiguate the two.)
		<P>

		<LI>If a vhost that would otherwise be a name-vhost includes a
		<CODE>Port</CODE> statement that doesn't match the main_server
		<CODE>Port</CODE> then it will be considered an IP-based vhost.
		Then <CODE>find_virtual_server</CODE> will match it (because
		the ports associated with each address in the address set default
		to the port of the main_server) as the connection vhost. Then
		<CODE>check_hostalias</CODE> will refuse to check any other name-based
		vhost because of the port mismatch. The result is that the vhost
		will steal all hits going to the main_server address.
		<P>

		<LI>If two IP-based vhosts have an address in common, the vhost appearing
		later in the file is always matched. Such a thing might happen
		inadvertently. If the config has name-based vhosts and for some reason
		the main_server <CODE>ServerName</CODE> resolves to the wrong address
		then all the name-based vhosts will be parsed as ip-based vhosts.
		Then the last of them will steal all the hits.
		<P>

		<LI>The last name-based vhost in the config is always matched for any hit
		which doesn't match one of the other name-based vhosts.

		</UL>

		<H3><A NAME="whatworks">What Works</A></H3>

		<P>In addition to the tips on the <A HREF="dns-caveats.html#tips">DNS
		Issues</A> page, here are some further tips:

		<UL>

		<LI>Place all main_server definitions before any VirtualHost definitions.
		(This is to aid the readability of the configuration -- the post-config
		merging process makes it non-obvious that definitions mixed in around
		virtualhosts might affect all virtualhosts.)
		<P>

		<LI>Arrange your VirtualHosts such
		that all name-based virtual hosts come first, followed by IP-based
		virtual hosts, followed by any <SAMP>_default_</SAMP> virtual host
		<P>

		<LI>Avoid <CODE>ServerPaths</CODE> which are prefixes of other
		<CODE>ServerPaths</CODE>. If you cannot avoid this then you have to
		ensure that the longer (more specific) prefix vhost appears earlier in
		the configuration file than the shorter (less specific) prefix
		(<EM>i.e.</EM>, "ServerPath /abc" should appear after
		"ServerPath /abcdef").
		<P>

		<LI>Do not use <EM>port-based</EM> vhosts in the same server as
		name-based vhosts. A loose definition for port-based is a vhost which
		is determined by the port on the server (<EM>i.e.</EM>, one server with
		ports 8000, 8080, and 80 - all of which have different configurations).
		<P>

		</UL>

		<!--#include virtual="footer.html" -->
		</BODY>
		</HTML>

docs/manual/vhosts/virtual-host.html

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