Apache HTTP Server Version 2.2
Apache HTTP Server Version 2.2
| Description: | Group authorizations based on host (name or IP address) |
|---|---|
| Status: | Base |
| Module Identifier: | authz_host_module |
| Source File: | mod_authz_host.c |
| Compatibility: | Available in Apache 2.1 and later |
The directives provided by mod_authz_host are
used in <Directory>,
<Files>, and
<Location> sections
as well as .htaccess
files to control access to particular parts of the server.
Access can be controlled based on the client hostname, IP address, or
other characteristics of the client request, as captured in environment variables. The Allow and Deny directives are used to
specify which clients are or are not allowed access to the server,
while the Order
directive sets the default access state, and configures how the
Allow and Deny directives interact with each
other.
Both host-based access restrictions and password-based
authentication may be implemented simultaneously. In that case,
the Satisfy directive is used
to determine how the two sets of restrictions interact.
In general, access restriction directives apply to all
access methods (GET, PUT,
POST, etc). This is the desired behavior in most
cases. However, it is possible to restrict some methods, while
leaving other methods unrestricted, by enclosing the directives
in a <Limit> section.
| Description: | Controls which hosts can access an area of the server |
|---|---|
| Syntax: | Allow from all|host|env=[!]env-variable
[host|env=[!]env-variable] ... |
| Context: | directory, .htaccess |
| Override: | Limit |
| Status: | Base |
| Module: | mod_authz_host |
The Allow directive affects which hosts can
access an area of the server. Access can be controlled by
hostname, IP address, IP address range, or by other
characteristics of the client request captured in environment
variables.
The first argument to this directive is always
from. The subsequent arguments can take three
different forms. If Allow from all is specified, then
all hosts are allowed access, subject to the configuration of the
Deny and Order directives as discussed
below. To allow only particular hosts or groups of hosts to access
the server, the host can be specified in any of the
following formats:
Allow from apache.org
Allow from .net example.edu
Hosts whose names match, or end in, this string are allowed
access. Only complete components are matched, so the above
example will match foo.apache.org but it will not
match fooapache.org. This configuration will cause
Apache to perform a double reverse DNS lookup on the client IP
address, regardless of the setting of the HostnameLookups directive. It will do
a reverse DNS lookup on the IP address to find the associated
hostname, and then do a forward lookup on the hostname to assure
that it matches the original IP address. Only if the forward
and reverse DNS are consistent and the hostname matches will
access be allowed.
Allow from 10.1.2.3
Allow from 192.168.1.104 192.168.1.205
An IP address of a host allowed access
Allow from 10.1
Allow from 10 172.20 192.168.2
The first 1 to 3 bytes of an IP address, for subnet restriction.
Allow from 10.1.0.0/255.255.0.0
A network a.b.c.d, and a netmask w.x.y.z. For more fine-grained subnet restriction.
Allow from 10.1.0.0/16
Similar to the previous case, except the netmask consists of nnn high-order 1 bits.
Note that the last three examples above match exactly the same set of hosts.
IPv6 addresses and IPv6 subnets can be specified as shown below:
Allow from 2001:db8::a00:20ff:fea7:ccea
Allow from 2001:db8::a00:20ff:fea7:ccea/10
The third format of the arguments to the
Allow directive allows access to the server
to be controlled based on the existence of an environment variable. When Allow from
env=env-variable is specified, then the request is
allowed access if the environment variable env-variable
exists. When Allow from env=!env-variable is
specified, then the request is allowed access if the environment
variable env-variable doesn't exist.
The server provides the ability to set environment
variables in a flexible way based on characteristics of the client
request using the directives provided by
mod_setenvif. Therefore, this directive can be
used to allow access based on such factors as the clients
User-Agent (browser type), Referer, or
other HTTP request header fields.
SetEnvIf User-Agent ^KnockKnock/2\.0 let_me_in
<Directory /docroot>
Order Deny,Allow
Deny from all
Allow from env=let_me_in
</Directory>
In this case, browsers with a user-agent string beginning
with KnockKnock/2.0 will be allowed access, and all
others will be denied.
| Description: | Controls which hosts are denied access to the server |
|---|---|
| Syntax: | Deny from all|host|env=[!]env-variable
[host|env=[!]env-variable] ... |
| Context: | directory, .htaccess |
| Override: | Limit |
| Status: | Base |
| Module: | mod_authz_host |
This directive allows access to the server to be restricted
based on hostname, IP address, or environment variables. The
arguments for the Deny directive are
identical to the arguments for the Allow directive.
| Description: | Controls the default access state and the order in which
Allow and Deny are
evaluated. |
|---|---|
| Syntax: | Order ordering |
| Default: | Order Deny,Allow |
| Context: | directory, .htaccess |
| Override: | Limit |
| Status: | Base |
| Module: | mod_authz_host |
The Order directive, along with the
Allow and Deny directives, controls a
three-pass access control system. The first pass processes either
all Allow or all
Deny directives, as
specified by the Order directive. The second
pass parses the rest of the directives (Deny or Allow). The third pass applies
to all requests which do not match either of the first two.
Note that all Allow and Deny directives are processed,
unlike a typical firewall, where only the first match is used. The
last match is effective (also unlike a typical firewall).
Additionally, the order in which lines appear in the configuration
files is not significant -- all Allow lines are processed as one
group, all Deny lines
are considered as another, and the default state is considered by
itself.
Ordering is one of:
Allow,DenyAllow directives are
evaluated; at least one must match, or the request is rejected.
Next, all Deny
directives are evaluated. If any matches, the request is rejected.
Last, any requests which do not match an Allow or a Deny directive are denied by
default.Deny,AllowDeny
directives are evaluated; if any match, the request is denied
unless it also matches an Allow directive. Any requests
which do not match any Allow or Deny directives are
permitted.Mutual-failureOrder
Allow,Deny and is deprecated in its favor.Keywords may only be separated by a comma; no whitespace is allowed between them.
| Match | Allow,Deny result | Deny,Allow result |
|---|---|---|
| Match Allow only | Request allowed | Request allowed |
| Match Deny only | Request denied | Request denied |
| No match | Default to second directive: Denied | Default to second directive: Allowed |
| Match both Allow & Deny | Final match controls: Denied | Final match controls: Allowed |
In the following example, all hosts in the apache.org domain are allowed access; all other hosts are denied access.
Order Deny,Allow
Deny from all
Allow from apache.org
In the next example, all hosts in the apache.org domain are
allowed access, except for the hosts which are in the foo.apache.org
subdomain, who are denied access. All hosts not in the apache.org
domain are denied access because the default state is to Deny access to the server.
Order Allow,Deny
Allow from apache.org
Deny from foo.apache.org
On the other hand, if the Order in the
last example is changed to Deny,Allow, all hosts will
be allowed access. This happens because, regardless of the actual
ordering of the directives in the configuration file, the
Allow from apache.org will be evaluated last and will
override the Deny from foo.apache.org. All hosts not in
the apache.org domain will also be allowed access
because the default state is Allow.
The presence of an Order directive can
affect access to a part of the server even in the absence of
accompanying Allow
and Deny directives
because of its effect on the default access state. For example,
<Directory /www>
Order Allow,Deny
</Directory>
will Deny all access to the /www directory
because the default access state is set to
Deny.
The Order directive controls the order of
access directive processing only within each phase of the server's
configuration processing. This implies, for example, that an
Allow or Deny directive occurring in a
<Location> section
will always be evaluated after an Allow or Deny directive occurring in a
<Directory>
section or .htaccess file, regardless of the setting of
the Order directive. For details on the
merging of configuration sections, see the documentation on How Directory, Location and Files sections
work.