All servers, including ``caching only'' servers, should have a line as follows in the boot file to prime the name servers cache:
cache . root.cache
Do not put anything into your cache files other than root server information.
All cache files listed will be read in at named boot time and any values still valid will be reinstated in the cache. The root name server information in the cache files will be used until a root query is actually answered by one of the name servers in the cache file, after which that answer will be used instead of the cache file until the answer times out.
As with primary and secondary, you may specify a secondary server for a class other than IN by appending /class to the cache keyword, e.g., class/HS.