[ Thanks to Falko
Timme for this link. ]
“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)…”