Allow Directive

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: 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:

A (partial) domain-name
Example:



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.
A full IP address
Example:



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



The first 1 to 3 bytes of an IP address, for subnet restriction.
A network/netmask pair
Example:



A network a.b.c.d, and a netmask w.x.y.z. For more fine-grained subnet restriction.
A network/nnn CIDR specification
Example:



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:



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. 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.
Example:



In this case, browsers with a user-agent string beginning with KnockKnock/2.0 will be allowed access, and all others will be denied.