In short, the purpose of a Dynamic DNS service is to allow servers without a static IP to host services with minimal interruptions.For example, people at home with ADSL internet providers may find that their IP is changing every so often.While on its face this may seem an excessively friendly default, DNS data is essentially public (that's why its there) and the bad guys can get all of it anyway.However if the thought of anyone being able to transfer your precious zone file is repugnant, or (and this is far more significant) you are concerned about possible Do S attack initiated by XFER requests, then use the following policy.DNS (Domain Name Service) is one of the most basic services on the Internet.
Some of these are hobbyist sites doing it for fun and the odd donation, and other sites are commercial businesses using the service to generate traffic to sell other products such as domain name registrations, premium accounts, etc.
This statement is mutually exclusive with update-policy and applies to master zones only.
The example shows DDNS for three zones: the first disables DDNS explicitly, the second uses an IP-based list, and the third references a key clause.
This statement may be used in a zone, view or global options clause. IP address(es) that are allowed to transfer (copy) the zone information from the server (master or slave for the zone).
The default behaviour is to allow zone transfers to any host.