If you own your DNS servers, you should probably want to close recursive queries being gathered from your servers.

In named.conf edit the options directive and add:

options {
allow-transfer {Secondary Server IP; }; allow-recursion { 127.0.0.1; A.B.C/24; };

};

In secondary server:
add to options:

allow-transfer { none; }; allow-recursion { 127.0.0.1; A.B.C/24; };