from BIND 8.  See use-alt-transfer-source,
                        alt-transfer-source-v4 and alt-transfer-source-v6.

                        SECURITY: use-alt-transfer-source is ENABLED unless
                        you are using views.  This may caues a security risk
                        resulting in accidental disclosure of wrong zone
                        content if the master supplying different source
                        content based on IP address.  If you are not certian
                        ISC recommends setting use-alt-transfer-source no;
developer: marka
reviewer: explorer