| Option | IP_FILTER_RDNS | |
| Description | IP filter for filtering which IP addresses may be queried with the rdns()function orreverseDns()function. | |
| Introduced Version | 1.37 | |
| Default |  | |
        IP filter for filtering which IP addresses may be queried with
        the rdns() function or
        reverseDns() function.
      
        The syntax of the IP address list is a sequence, separated 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).
      
        For example, here we deny RDNS queries on the CIDR block
        192.168.0.0/16 and allow
        all others:
      
ini
IP_FILTER_RDNS=deny 192.168.0.0/16; allow all