IP filter for filtering which DNS servers may be specified in the
The syntax of these list is a sequence, seperated by newlines 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
18.104.22.168 and deny all others.
IP_FILTER_RDNS_SERVER=allow 22.214.171.124; allow 126.96.36.199; deny all