To disable caching on a name server, use the recursion options statement:
root# cat /etc/named.comf
Disabling recursion is one of the most effective ways to limit the amount of memory a name server uses.
Processing a recursive query often requires a name server to query another name server, and the name server then caches the response.
It’s caching that causes a name server’s memory usage to increase over time.
Unfortunately, you can’t disable recursion on just any old name server.
Many name servers serve one or more authorized resolvers, and those resolvers need their recursive queries answered, well, recursively.
Name servers used as forwarders must process recursive queries, too.