"Caching-Nameserver is a type of nameserver that will resolve a web addresses (domain names) from its next or master DNS, and will keep those entries in cache, after first time resolution it will resolve DNS queries locally, until its TTL (Time To Live) is expired.
"BIND 9 is used to resolve domain resolution queries from it own database, as it is SOA (Start Of Authority).
"So now it is clear that in our setup the caching-nameserver will be used to resolve domain names externally (internet), while BIND 9 will be used to resolve domain names from our local network (internally)..."
