b._dns-sd._udp.example.com.    PTR   Building 1.example.com.
                                   PTR   Building 2.example.com.
                                   PTR   Building 3.example.com.
                                   PTR   Building 4.example.com.

    db._dns-sd._udp.example.com.   PTR   Building 1.example.com.

    lb._dns-sd._udp.example.com.   PTR   Building 1.example.com.