VariableIP_FILTER_RDNS_SERVER
Introduced Version1.37
DescriptionIP filter for filtering which DNS servers may be specified in the rdns function
Default 

IP filter for filtering which DNS servers may be specified in the rdns function.

The syntax of these list is a sequence, seperated by newlines or ;, of allow or deny actions, along with a CIDR block or all. An IP address is allowed or denied by finding the first match and applying the corresponding action. The all value matches any IP-address (i.e., IPv4 or IPv6).

Note that this only restricts what may be specified - if no server is specified then the system default or the one specified by RDNS_DEFAULT_SERVER will be used irrespective of whether it is blocked by this filter.

For example, here we restrict the server to 8.8.8.8 and 1.1.1.1 and deny all others.

ini files
IP_FILTER_RDNS_SERVER=allow 8.8.8.8; allow 1.1.1.1; deny all