My secondary server for both an internal and an external view has both views transferred from the same primary view - how to resolve?

BIND 9.10 and later: use the "in-view" zone option to allow both views to use the same in-memory instance of the zone.  See the ARM for your version of BIND for more details.

BIND 9.9 and later: see examples 3 and 4 of Understanding views in BIND 9, by example for an alternate method.

BIND 9.3 and later: Use TSIG to select the appropriate view.

Note the key must be specified before the address in the match-clients acls as processing of the ACL stops on first match.

Primary 10.0.1.1:

          key "external" {
                   algorithm hmac-md5;
                   secret "xxxxxxxx";
           };
           view "internal" {
                   match-clients { !key external; 10.0.1/24; };
                   ...
           };
           view "external" {
                   match-clients { key external; any; };
                   server 10.0.1.2 { keys external; };
                   recursion no;
                   ...
           };

Secondary 10.0.1.2:

          key "external" {
                   algorithm hmac-md5;
                   secret "xxxxxxxx";
           };
           view "internal" {
                   match-clients { !key external; 10.0.1/24; };

                   ...
           };
           view "external" {
                   match-clients { key external; any; };
                   server 10.0.1.1 { keys external; };
                   recursion no;
                   ...
           };