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Order 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:  Extension
 Module:  mod_access_compat

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,Deny
First, all Allow 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,Allow
First, all Deny 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.
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 example.org domain are allowed access; all other hosts are denied access.

Order Deny,Allow
Deny from all
Allow from example.org

In the next example, all hosts in the example.org domain are allowed access, except for the hosts which are in the foo.example.org subdomain, who are denied access. All hosts not in the example.org domain are denied access because the default state is to Deny access to the server.

Order Allow,Deny
Allow from example.org
Deny from foo.example.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 example.org will be evaluated last and will override the Deny from foo.example.org. All hosts not in the example.org domain will also be allowed access because the default state is Allow.

Allow Directive

 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: Extension
 Module: mod_access_compat

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:

A (partial) domain-name

Allow from example.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.example.org but it will not match fooexample.org. This configuration will cause Apache httpd to perform a double 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.
A full IP address

Allow from 10.1.2.3
Allow from 192.168.1.104 192.168.1.205

An IP address of a host allowed access
A partial IP address

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.
A network/netmask pair

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.
A network/nnn CIDR specification

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.

Deny Directive

 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: Extension
 Module: mod_access_compat

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.

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